Structures Congress 2015

Design of blast resistant windows is relatively new compared to other façade components such as steel, concrete, and reinforced masonry, but is slowly coming into its own in terms of design procedures and response criteria. Initial response criteria from the mid 1980s – when design procedures for blast resistant windows were initially formulated – limited window framing to L/264 but no more than 1/8-in. There were also stringent wall response criteria when windows attached directly to walls. These criteria were used because monolithic glazing, limited to low probabilities of fracture, was used. In the 1990s and early 2000s, when laminated glass started to become the glazing for blast resistant windows, software using SDOF approaches allowed for the fracture and even flyout of the glazing – depending on the level of protection to be used. However, frame response was still rather stringent and vacillated between L/60 and L/160 of the frame member. With the publication of the ASCE document on “Blast Protection of Buildings” and the PDC TR 10-02, “Blast Resistant Design Methodology for Window Systems Designed Statically and Dynamically”, frame response criteria for windows, storefront systems, and curtain walls became less stringent and varied depending on the level of protection to be used. Recent testing has shown that even the latest response criteria may be somewhat conservative for different levels of protection. The test information is somewhat limited since most window systems are tested to show compliance with different glazing hazard levels/performance conditions, but limited available data where deflection of mullions was tracked during dynamic loading, showed low glazing hazards even though frame response was greater than would be allowed for design. This paper presents a historical perspective of how response limits and glazing design have progressed over the years and then presents available data showing that low glazing hazards against blast loads can be achieved even though the frame response is much greater than the current allowable limits.

This paper provides architects and engineers with an overview of key factors to consider when designing facade envelope components against wind, seismic and blast loads. Examples and situations that may be encountered in the design of curtainwall, storefronts and other façade components are presented along with “lessons-learned” recommendations on how to effectively deal with or avoid design problems. “Typical approaches” for designing envelope components are illustrated and existing government and industry criteria for wind, seismic and blast loads are reviewed and discussed.

The last two years have witnessed a number of new cable-stay bridge design awards in the US, many of those bridges call explicitly for the development of a Threat, Vulnerability and Risk Assessment (TVRA) and for a design to mitigate the effects of improvised explosive devices and accidental or intentional fire threats, typically tankers. The subject of intentional fire effects on bridge has received little attention compared to blast effects. Prescriptive approaches that rely on a rated duration when exposed to a UL 1709 hydrocarbon fire curve are poorly correlated to specific fire threat scenarios which must be addressed in a TVRA. A simple application of such traditional approaches can yield designs that are potentially uneconomical, but more importantly can steer the engineer away from more thoughtful and resilient designs. A performance-based design offers a more rational risk-based approach that rewards good design practices. However, performance-based design requires a rigorous physics-based approach to analyzing vulnerabilities and assessing mitigations. This paper examines a rational approach as it applies to critical components of a cable-stay bridge. It discusses accidental and intentional fire threats, critical bridge members that could be susceptible to such events, physics-based computational analysis methods to accurately evaluate the consequences of such events, and candidate mitigation measures using performance based criteria. This methodology has been applied to actual cable-stay bridge designs in the US. Examples in this paper however are developed for generic yet representative bridge components.

Blast-resistant windows are typically made of laminated glass. Laminated glass consists of two or more layers of glass bonded to a relatively low strength but ductile interlayer, such as polyvinyl butyral (pvb). The glass layers fracture under applied blast loads, but the system deforms in a ductile manner as a tension membrane develops to resist the load and restrain the shattered glass. This tension membrane capability represents a significant portion of the blast resistance or capacity of the glazing system and imparts in-plane loads to the window frame. Structural sealant is typically used to glaze the glass to the frame. This sealant transfers the tensile membrane forces to the surrounding frame and/or mullions and ultimately to the supporting wall through anchors. Commonly used analytical models provide edge reactions for the glazing based on the resistance function for a Single Degree of Freedom (SDOF) system of lite assuming rigid supports. This assumption, that in-plane displacements are zero, can cause under-prediction of out-of-plane displacements because in reality the supports exhibit in-plane flexibility. This paper discusses the effect of the structural silicone, applied along the glazing edges, on the tensile forces transferred into the window frame and then to the supporting structure. Structural silicone is modeled as a flexible support with non-linear properties for the in-plane forces acting along the glass edge. Two models are developed, assuming one-way response, for: 1) rigid supports, and 2) flexible supports. The effect of the restraining conditions on the dynamic response of the glazing system was investigated using simplified dynamic models and then compared to advanced analytical dynamic methods using finite element analysis (FEA). The results showed good agreement with the simplified models indicating that the proposed simplified procedures can be used to include the effects of the glazing restraints in the overall design of the window frame and the supporting structural system. Finally, a Multi-Degree-of-Freedom (MDOF) tool was developed which included the proposed simplified formulation and then compared against SDOF response with rigid supports. Recommendations are provided regarding the inclusion of in-plane reaction load for the window and anchorage design.

An accidental load drop during load handling could impact the safety of the nuclear plant structures or safety-related equipment and cause inadvertent criticality, or loss of safe shutdown equipment. In this paper, available approaches for evaluation of the structural members due to impact of an accidental load drop in US nuclear power plants are evaluated. Consideration is given to the limitations of the approaches imposed by the NUREG-0612 (1980). The paper discusses the two common approaches that can be used to evaluate the impact: the first approach is to calculate the elasto-plastic energy absorption capacity of the member and compare it to the energy imparted during impact. The second is to estimate the applied force on the impacted member considering the penetration of the load into the target using empirical formulas. The limitations of each approach are demonstrated by evaluation of a hypothetical structural beam. Both approaches are investigated to calculate the allowable load at a given drop height for various drop locations along the beam centerline, as well as off-centerline of the beam. Additionally, a sensitivity study is performed to consider the effect of boundary conditions on the results in terms of the load drop capacity. Based on the results of the analysis, recommendations are given for the proper selection of the approach to estimate the allowable drop load based on the load drop location.

The Lattice Discrete Particle Model (LDPM), a meso-scale model for concrete, was extensively calibrated and validated in previous research for quasi-static loading conditions. In this paper, LDPM is used to investigate the time-dependent behavior of concrete for high strain rates with the main objective of (1) assessing the role of apparent and intrinsic rate effect mechanisms on the macroscopic concrete response; and (2) demonstrating LDPM predictive capabilities under dynamic loading conditions. The LDPM formulation is extended to incorporate rate-dependent fracture mechanisms associated with the interpretation of fracture processes as thermally activated phenomena and governed by the classical Maxwell-Boltzmann theory. According to this approach, the LDPM meso-scale strength and toughness are assumed to be functions of the meso-scale strain rate. The model is calibrated and validated on the basis of experimental data available in the literature and obtained through (a) reinforced and unreinforced unconfined compression tests; and (b) Hopkinson bar tests in tension and compression. Analysis of the numerical results shows the ability of LDPM to simulate accurately the dynamic response of concrete under a large variety of loading conditions. Furthermore, in this study, LDPM is used to perform simulations of projectile impacts on regular strength concrete (RSC) and high strength concrete (HSC). Perforation and penetration experiments on RSC and HSC for varied impact velocities are carried out and the exit velocities are compared to available experimental data. In general, LDPM replicates successfully the behavior of concrete for penetration and perforation events and it is able to capture accurately the main features of concrete response in terms of projectile deceleration as well as fracture patterns.

Steel-plate composite (SC) walls have been used recently in overseas and domestic nuclear power plant (NPP) projects. For safety-related NPP facilities these walls may be required to resist the effects of impact. Analysis of the structural global response of conventional reinforced concrete (RC) walls to impact loadings, such as those from tornado borne missiles or turbine-generated missiles and secondary wall impacts due to heavy load drops, is reasonably approximated using simplified dynamic analysis methods. For cases in which global bending dominates the response, an inelastic single-degree-of-freedom (SDOF) model is effective. For some impact loadings the response includes considerable localized deformation. Analysis for these cases requires a cascaded two-degree-of-freedom (TDOF) model with one mass and resistance representing the global flexural response and a second mass, resistance and damping representing the local deformation response. In this paper, the methodology to complete dynamic analysis of impact loadings on SC walls (both SDOF and TDOF models) is provided, and SDOF and TDOF model results are compared to SC wall dynamic response from nonlinear finite element models.

Accurate prediction of material properties under combined high strain rate and elevated temperature are essential for safe design of structures to withstand post-impact fire situations such as collision by heavy vehicles followed by fire. Numerous material tests performed in recent years do not address the influence of such sequential loading on the mechanical properties of mild steel. An inclusive test program is carried out in the Civil Engineering Lab at Monash University to investigate the post-impact fire properties of Grade 350 structural steel and the results are presented here. Specimens have undergone interrupting high strain rate tensile loading, controlled locally at defined levels of elongation, to account for different deformation states. Different damage levels are introduced for each rate of strain with respect to the displacement corresponding to the ultimate stress (f_u). Subsequently, the partly damaged specimens are subjected to static tensile loading to failure at high temperature conditions. Material behaviour of pre-damaged steel is compared to those of each individual loading scenario and to design code expressions. The test results demonstrate that the combined actions are profoundly different from that in which the structure is subjected to either high strain rate or thermal loading and notably vary from those predicted in different codes. Moreover, it is shown that the strength and ductility of mild steel are significantly dependent on the rate of loading, the pre-deformation history and the temperature it is subsequently exposed to. The experimental results can be used by researchers and structural engineers as benchmark data for calibrating current material model constants and/or developing new material models which take into account the coupled effect of high strain rate and temperature for rational fire analysis and design of steel structures.

The Unified Facilities Criteria (UFC) 3-340-02, formerly Army Technical Manual 5-1300/NAVFAC P-397/AFR 88-22 (TM 5-1300), defines the criteria for designing reinforced concrete structures to resist blast effects from accidental explosions. The recent Change 1 to the UFC 3-340-02 included an update to section 4-21.8 “Mechanical Splices of Reinforcement.” This update added the validation test requirements and the acceptance criteria for the use of mechanical couplers in place of lap splicing of steel reinforcing bars in elements at specific locations and under certain conditions. Several types of mechanical couplers have been tested and validated for developing the strength of reinforcing steel for cyclic loading and strain-rates expected during earthquakes. However, no mechanical couplers were shown to meet the longstanding section 4-21.8 requirement that the coupler be capable of developing the ultimate dynamic tensile strength of the reinforcing bar under high strain-rate loading without reducing its ductility. This paper presents the results of tests performed by the U.S. Army Engineer Research and Development Center (ERDC) and documented in ERDC Technical Report TR-09-8, “High Strain-Rate Testing of Mechanical Couplers.” Five different types of mechanical couplers that meet the American Concrete Institute 318 type II requirements were dynamically tested at low, medium, and high strain-rates to obtain their measured performances. The performances of these mechanical couplers were compared to control bars tested at the same strain-rates. The test results were evaluated to determine if requirements of TM 5-1300 and UFC 3-340-02 were achieved. While the evaluation showed that these five mechanical couplers did not consistently meet the section 4-21.8 requirement for unrestricted use, the tests did demonstrate adequate performance for certain couplers at lower response limits. The recent Change 1 of the UFC 3-340-02 is discussed and compared to the previous requirements to provide the industry guidance and a path forward to further testing and validation of mechanical couplers for use in hardened structures.

An elevated one-story steel control building in a Liquefied Natural Gas (LNG) facility was originally designed to resist wind and moderate seismic loads. Due to a change in the facility layout, the building became subjected to risk from a vapor cloud explosion. It was determined that the existing design could not withstand this over-pressure and due to schedule and operational constraints by the facility owner, the existing design required retrofitting to resist the blast over-pressures. The paper presented, utilizes the single degree of freedom (SDOF) and the multi-degree of freedom (MDOF) approach for performing a non-linear dynamic analysis to minimize the extent of retrofits to the control building without impacting foundation design or operational conditions.

The structural robustness of buildings is related to their capacity to redistribute loads after a local failure preventing progressive collapse. The energy absorption capacity of structural elements allows estimating both, their static and dynamic load-bearing capacities and therefore is a key parameter for robustness assessments. This paper presents a methodology to calculate the static load-deflection relationship of laterally unrestrained reinforced concrete (RC) slabs by means of three different stages: an elastic stage, a transitional elastic-plastic stage and a membrane action stage. Membrane forces are estimated from the kinematic relationships of the slab and equilibrium considerations. This approach includes different failure criteria in order to estimate the total energy absorption capacity of these slabs.

There are many computational procedures that can be used to analyze and design protective structures to a blast threat. In practice, the complexity of the analysis and design procedures is dictated by whether the facility to be protected is mandated to meet prescriptive protection requirements, on one hand, or the facility is desired to be designed with consideration to one or more design basis explosive threats. The simplest analysis approaches typically suffice for the former case, while the more complex analysis and design approaches become important for the latter. In either case, however, the primary function of the blast effects calculations is to calculate blast loads from which to design the protective structure. This paper identifies and explores scenarios where secondary debris can affect the response of the protective structures and that can necessitate considering their loading effects when designing them. Examples include the effects of debris from vehicle borne threats and secondary debris generated by an overloaded structure. We describe both simplified and complex physics-based computational approaches that can be used to quantify their loading effects on protective structures, including fast-running simplified models up to complex models employing coupled computational fluid dynamics (CFD) and computational solid dynamics (CSD) approaches. We describe the advantages and limitations associated with each computational approach.

Conventional reinforced concrete (RC) structures have historically been the preferred choice for blast and impact resistant structures. Recent research demonstrates advantages of steel-plate composite (SC) structures that make them an excellent candidate for efficient construction of protective structures. Understanding of the behavior, analysis, and design of SC walls for safety-related nuclear structures in the US and abroad has advanced in the past decade resulting in the publication of a new specification for their design. A body of knowledge also exists to design SC structures to resist the effects of projectile impacts. Research on the behavior of SC walls subjected to blast does not exist in the public domain—a loading which has been identified as a continuing concern for protective structure design. This paper summarizes results from blast tests of SC walls.

Current design codes do not deal with bridge fires despite their catastrophic consequences, especially when the bridge deck is built with steel I-girders. The most advanced approach to study the fire response of a bridge is the use of Computational Fluid Dynamics (CFD) models to simulate the fire scenarios coupled with FE thermo-mechanical models. In the case of steel girder bridges, FE models usually include a single girder and not the full deck to make the analyses required much simpler and less time consuming. In this paper, the validity of this assumption is verified. To reach this goal, the fire response of a steel girder bridge spanning 21.34 m is obtained using single girder and full deck FE models. Results show that single girder models can reasonably predict the failure time and failure mode of the most damaged bridge girder, although their estimation of the final deflections are not so good.

Oversized and overweight Rough Terrain (RT) and All Terrain (AT) commercial cranes are used extensively at dam projects and continuously cross bridges that serve the requirements of the public agencies or private utilities that own them. Depending on the state jurisdiction, these cranes will be trailered or driven under a variety of local and multistate permit programs. The effects of crane loads on highway bridges are a frequent concern due to the variability in age, design, construction, and condition of the bridges. Currently, the only guidance available for analysis is criteria outlined in AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications and AASHTO Guide Manual for the Condition Evaluation and Load and Resistance Factor Rating of Highway Bridges (LRFR). The information in this presentation will help determine safe loading capacity and placement of three common types of classifications of oversized cranes on a bridge. It is based on vehicular loading and requires an analysis methodology that extrapolates an allowable crane permit loading from the LRFR bridge design or legal loading. The differences between vehicular & crane live and static loads, axle configurations, and load placements are discussed. There are recommendations for making informed decisions on adjustments in impact loads, live load distributions and lane loading based on the Strength II requirements outlined in the evaluation and rating procedures in the AASHTO LRFR and LRFD specifications. This article will also show an outline for planning a crane operation on a bridge that includes consideration of working loads, placement and minimizing risks.

Hurricanes, such as Ivan and Katrina, impacting the northern gulf coast have caused damage to coastal bridges. The storm surge resulting from these hurricanes was large enough to allow waves to impact the bridge superstructure and remove the bridge sections from the pile caps which support them. Due to the widespread effects of coastal storms, which generally create governing design criteria for coastal bridges, this topic is of national and international interest. Since the occurrence of those storms, several organizations have created new methodologies for estimating wave forces. Two of the most widely accepted methods are the ones outlined by the Federal Highway Administration Hydraulic Engineering Circular 25 (HEC 25) and by AASHTO in the 2008 Guide Specifications for Bridges Vulnerable to Coastal Storms. Proper estimation of wave loads is essential when designing vertical and lateral restraints for bridge decks. This paper will evaluate the HEC 25 method using a new data set which has been published since the original development of these methods. This paper will also re-evaluate guidance for the empirical coefficients suggested for the HEC 25 method. Because of that method’s relative simplicity, the general equations outlined in HEC 25 are easier to use and less confusing than other methods, this effort is justified in light of the new data sets. An improved methodology was created by refining the guidance for estimating wave loads on bridge decks. This new methodology demonstrates a significant increase in the reliability of wave load estimates on a bridge superstructure during severe storm conditions. This guidance will allow engineers to more effectively choose the necessary coefficients, which will in turn help to more effectively estimate wave loads.

Recently, the design and fabrication of a proposed orthotropic deck for a vertical lift bridge were evaluated for infinite fatigue life by testing a full-size prototype of the part bridge deck at the ATLSS Engineering Research Center of Lehigh University. Contrary to the more conventional orthotropic decks, the design incorporated a thicker deck plate stiffened by round bottom ribs and fitted floor beams (FB). Although similar details have been implemented in service, infinite life fatigue performance of the deck for the proposed geometric parameters was not known. Multilevel 3D Finite Element Analyses (FEA) were performed to design the specimen and the test set up for adequately reproducing the design stresses due to AASHTO fatigue loading. The study provided critical information on issues related to cost-effective fabrication and rational fabrication tolerances, and established a life-cycle cost-effective standard orthotropic deck design that can provide a service life exceeding 100 years with minimum maintenance.

The center beam (CB) to support bar (SB) connections in modular bridge joint systems (MBJS) in highway bridges are especially susceptible to fatigue cracking under repeated loading from crossing truck traffic, necessitating infinite life design of these connections. Welded CB-SB connections within multiple support bar (MSB) systems are more common in the United States; however, in-service performance of bolted CB-SB stirrup connections within single support bar (SSB) systems in other countries suggests that they can be successfully used to provide infinite life and higher fatigue resistance if adequately designed. The fatigue resistance of these connections has not been fully established within the AASHTO specifications. Recently, bolted SSB MBJS was evaluated by full scale testing of subassemblies at Lehigh University, which demonstrated an infinite life fatigue resistance of AASHTO Category B (currently specified as Category D) for CB-SB connections with adequate pretension. Revisions to the AASHTO specifications were proposed based on this study.

To decouple the heavy rail entrance into the Port of Vancouver USA from a major north/south mainline of the nation’s rail system, a rail-under-rail grade-separation structure was designed along the northern bank of the Columbia River in Vancouver, Washington. To provide the required 23.5 foot (7.2 meter) clearance below an existing 100-year old rail bridge that crosses the river, the new rail line needed to descend more than 14 feet (4.3 meters) below the 100-year flood elevation. Because trains need to remain in operation during this flood condition, protection of the rail line from flood waters was required. Several innovative design solutions were developed to meet this design criteria in the most efficient manner. This case study is of regional, national, and international interest. The paper will discuss the project’s constraints, design challenges, and solutions utilized to meet the project criteria. The location and configuration of the structure posed special challenges and the solutions for this project will be of interest to practicing structural engineers as well as rail operators, owners, and land use professionals. The rail structure itself, a 1,350-foot (411.5 meter) long portion of the new rail entrance for the port, is a partially elevated reinforced concrete structure that protects the rail from flood waters and supports it along the irregular river bank. To resist flood waters, a continuous reinforced concrete U-shaped trench was selected as the optimal solution. This selection of structure type was the first of many challenges for this project. The superstructure borrows design innovations from the continuously reinforced concrete pavement industry to help eliminate expansion joints over the entire length of the structure. This helps minimize water infiltration during flood events and reduces lifetime maintenance costs. The substructure consists of closely spaced driven steel batter piles that support the majority of the rail trench structure and is extremely compatible with the expansion joint-free design. The new rail trench structure provides a unique facility that meets the design challenges of the site, maximizes operational efficiency for the port, and relieves congestion at this critical location along the Pacific Northwest’s high-speed rail corridor.

For decades, the 1906 Hoover Mason Trestle at the historic Bethlehem Steel plant in Bethlehem, PA, supported ore-filled rail cars transporting raw materials from the Ore Yard to the steel plant’s large furnaces, five of which remain standing. After being left to decay for several decades, the Trestle is getting a new life as the backbone of a new, half-mile long promenade that will offer unique and publicly-accessible views into the historic steel plant, the new SteelStacks Campus, and surrounding town. The architectural design of the walkway follows a sinuous path both vertically and horizontally along the linear railway tracks. The underlying structure of the walkway is a series of wide flange post and beam ‘bents’ with ‘feet’ that affix to the train rails. The bent’s horizontal girders vary in length, cantilevering to one or both sides of the posts to accommodate the varying geometry of the walkway. Affixing the posts to the rails offered a uniform connection type and methodology. Between the main steel bents, secondary steel beams support one of three features: cast-in-place concrete walkways on steel deck, steel bar-grating walkways, or cast-in-place concrete planters on steel deck supporting up to 30 in. of soil and vegetation. Bearing on the existing historical structure created a variety of design challenges. Despite the original drawings and many of the repair and/or replacement drawings being available, several portions of the trestle have been reconstructed or heavily modified without documentation. This created complexities in understanding the limitations and opportunities in the existing framing.

San Francisco County Transportation Authority (SFCTA) selected AECOM and Moffatt & Nichol for the design of the new westbound entrance and exit ramps providing access between the new east-span of San Francisco-Oakland Bay Bridge (SFOBB) and Yerba Buena Island (YBI). The purpose of the project is to improve mobility, safety, and access by replacing two westbound existing ramps on I-80 constructed in the 1930s. The new ramps will be a significant improvement geometrically and operationally over the current ramps. They include bridge structures that complement the SFOBB architecture. The project was cleared under an EIR/EIS prepared by AECOM. The construction contract of the project has been awarded on late 2013, and construction completion is targeted for late 2016. The YBI WB on and off ramps consist of five structures: YBI WB Tie-In Viaduct (Widen) - a five-span cast-in-place prestressed concrete box girder supported on large-diameter CIDH foundation, YBI Transition Viaduct (On-Ramp Widen) - a two-span cast-in-place reinforced concrete box girder with a variable depth supported on driven pile foundations, YBI WB On-Ramp Structure- a two-frame, five-span concrete structure supported on driven pile foundation , YBI WB Off-Ramp Structure- a two-frame, six-span concrete structure, and YBI WB Transition Viaduct (Off-Ramp Widen)- a cast-in-place concrete deck with a single structure steel box girder. The WB Ramp Structures were designed to resist two-level earthquake, including a Functional Evaluation Earthquake (FEE) with a return period of about 92 years and a Safety Evaluation Earthquake (SEE) with a return period of about 1500 years. The terrain at the bridge site is highly variable with ground surface elevations varying from about +10 m to about +50 m.

This paper presents a reliability-based framework for dynamic analysis of long-span cable-stayed bridges (LSCSBs) subjected to cable breakage incidents with simultaneous presence of dynamic excitations from wind and traffic. Through the Latin Hypercube sampling technique, a series of simulation models are generated considering various sources of uncertainties stemmed from structural material properties, sectional properties, wind, vehicle composition, and cable breakage characteristics. The present study establishes the nonlinear fully coupled dynamic equations of the bridge-traffic system using the stochastic finite element approach, in which the dynamic coupling effects among bridge, wind and stochastic traffic are appropriately incorporated. Various sources of geometric and material nonlinearities are considered when cable breakage scenarios are investigated with realistic dynamic initial states. The failure probability of the bridge structure corresponding to strength and service limit states in a cable breakage event can be further obtained. After the proposed reliability framework is introduced, a prototype LSCSB is selected for a demonstration and some observations are discussed.

The Delair Bridge Span Replacement was a TIGER IIII project involving accelerated bridge construction methods applied to the upgrading of freight capacity of the Delair Bridge, spanning the Delaware River between New Jersey and Pennsylvania. The span replacement effort was logistically and procedurally complex. Through an integrated project management approach, the project’s planning, engineering, and construction management professionals worked collaboratively with federal and state agency staff, contractors, and Conrail staff to proactively identify obstacles and develop solutions that addressed the challenge without conflicting with prior authorizations or compromising future activity. In the field, substantial pre-outage preparation, including intensive coordination with bridge stakeholders, physical preparation of the structure, and pre-fabrication of the replacement spans, enabled span replacement to proceed smoothly and efficiently, with all work completed within each 72-hour outage. The Delair Bridge Span replacement project was completed one year ahead of schedule with more than $11M in total budget savings. This savings left more than $5M in federal cost share that was reallocated by USDOT to other critical freight rail infrastructure projects in South Jersey.

This paper summarizes a cooperative project to assess the current condition and life expectancy of 132 timber highway bridge superstructures at locations throughout the United States. Several superstructure types were included in this comprehensive effort, of which two-thirds were sawn timber stringer systems. In-depth inspections were conducted by the project team using visual, probing, and nondestructive evaluation (NDE) techniques to characterize the condition of the primary bridge superstructure components. The condition of the bridges was satisfactory and better for large percentages of the superstructure subsets, even within those regions of the country that have higher hazard ratings for exposed wood structures. Inspection results show that timber is a viable option for primary structural members in highway bridges with satisfactory service-life estimation of 70 years or more. These results shall provide the basis for the development of life-cycle cost analyses and bridge deterioration rate modeling for timber bridge superstructures in the future.

Bridge owners often view timber bridges with suspicion. Can a timber bridge carry the required highway design loading? Will a timber bridge last 75 years? Are there crash-tested rail systems available? Can a durable wear surface be installed on a timber deck? Is the preservative treatment environmentally safe? These are some of the concerns raised when considering a timber bridge option. The timber industry has addressed each of these concerns and today’s timber bridges are performing exceptionally well. This paper discusses each of these items and explains how Modern Timber Bridges meet and exceed the expectations of today’s bridge owners.

The 1617 meter long Coos Bay (McCullough Memorial) Bridge was completed in 1936 as part of a Public Works Administration project that constructed five major river and bay crossings on the Oregon Coast Highway. The five bridges were designed under the direction of Oregon’s renowned bridge designer Conde B. McCullough and each bridge showcases McCullough’s skill in weaving aesthetic values into functional, economical structures that “fit” their unique sites. The McCullough Bridge is an unusually pleasant example of a cantilever truss that harmonizes with the arches of its approach spans. Since 2007, the Oregon Department of Transportation (ODOT) has been engaged in rehabilitation work on the Coos Bay (McCullough) Bridge. This work has included painting of structural steel members, impressed current cathodic protection of the north and south approaches, a polyester deck overlay, drainage improvements, seismic improvements, and installation of a replica historic “stealth” rail. This paper will use the Coos Bay Bridge projects as a case study to showcase the state of practice for bridge preservation in ODOT. In recent years, this practice has broadened in response to economic pressures and reductions in preservation costs, which are driving the application of bridge preservation techniques beyond historic bridges into “workhorse” bridges.

Sensing technology has the ability to provide information that can answer difficult questions with regard to constructed bridge behavior improving the way complex structures are maintained. A detailed evaluation of the State Route 61 Bridge in Clinton, TN is prime example. The Route 61 Bridge is a 3-span continuous steel girder bridge that includes several complex features; the structure has a kinked-girder alignment, steel integral pier caps, skewed substructures, and one integral abutment. It was built in 1985, rehabilitated significantly in 1996, and is again scheduled for a rehabilitation in the upcoming year. The current structure has a failed expansion joint, severely tilted expansion bearings, and includes substantial concrete degradation at the ends of the structure. As a result, a detailed assessment was performed that included the application of sensing technology for field measurements along with numerical finite element modeling. Vibrating wire technology was utilized for measurement of relative bearing movement as well as girder strains over a period of three months. In addition, global movement was measured at select times with survey equipment. After collection and review of the data it was determined that unexpected thermal movement was the primary cause of the increased bridge deterioration. Recommendations were made for the upcoming rehabilitation to increase the life of the structure.

The Huey P. Long Bridge is a four-span steel truss bridge that carries a two-track railroad line over the Mississippi River in New Orleans with two lanes of US 90 on each side of the central tracks owned by the New Orleans Public Belt Railroad. A bridge widening project was initiated to include two new vertical planes of trusses on the outside of the bridge and add additional lanes and shoulder over the complete four-span river crossing. As part of the overall bridge widening project, specifications were included in the construction documents to provide a truss monitoring system to compare actual versus predicted response of the bridge structure throughout the construction process of the original stick-build bid design. This monitoring system was intended to mitigate risk to the owner throughout the construction operation. When the contractor was awarded the project, a different method of construction was proposed where pairs of 528-ft long, 2700-ton trusses were built near shore on barges, barged in place under the bridge, lifted in pairs and skidded in place. A real-time remote monitoring system was designed and implemented to measure truss distortion and assure overstressing or buckling of the truss did not occur during the transport, lift and skidding operation. Data were under constant review to limit ‘sweeping’ of the truss during the lifting and skidding operation. This monitoring system was used to mitigate risk to the Contractor for the three pairs of heavy truss lifts.

Instrumentation of bridges, through targeted short term test applications to long term health monitoring applications, has become more widespread and accepted as means for supporting traditional engineering where current practice fails to provide a clear path forward. While decreased costs associated with data acquisition and sensor hardware are supporting applications with large arrays of sensor nodes, there are still significant costs associated with data reduction, processing, and interpretation of large datasets. Engineers involved with monitoring applications must be cognizant of this fact, and streamline system designs to focus a fixed quantity of manageable sensors to the areas of greatest uncertainty in terms of structural performance. This paper introduces a long span bridge in the United States which was found to have unsatisfactory ratings for structural elements at different locations along the main load carrying path. The structure contains many internal movement mechanisms, as it is a cantilevered truss with intermittent simply supported trusses. A load test was carried out using up to six fully loaded tri-axle dump trucks. During the processing and interpretation of results, it was clear the structure was performing in a non-linear fashion, based upon the location of the load. Through a detailed finite element model calibration effort, using state of the art optimization techniques, it was found that depending on the location of load on the structure, the primary load carrying path of the truss changed, and assumptions regarding the performance of movement mechanisms were modified. Through the detailed analysis, the engineer of record was able to provide updated ratings and recommendations to the owner of the structure, whose aim is to indefinitely preserve the structure due to its critical function within the regional transportation network. A main contribution of this presentation is the important consideration to implementers of monitoring techniques to consider that such applications must be able to defend major assumptions placed on structural performance, such as them being linear and stationery.

Tsunamis have caused significant damage to coastal communities in recent years. For example, the 2011 Great East Japan Earthquake and resulting Tohoku Tsunami destroyed infrastructure along the east coast of Japan including bridge superstructures. Highway bridges, as an important part of transportation system, have a significant role in maintaining access to coastal communities after a tsunami. Therefore, tsunami-resistant design of these superstructures is crucial. This study provides a novel methodology developed for bridge superstructure design under tsunami loads and aims to help bridge design professionals better understand structural behavior of bridges during tsunamis. An approach to estimate the tsunami loads on bridge structures and assess the structural response of the bridge is presented. Results of numerical simulations performed to compute loads on a coastal bridge are summarized and analyzed. In addition, the load effects on a particular coastal bridge due to the impact of a tsunami are discussed.

Assessing the current condition of structures and infrastructure systems has long been critical to ensure their effectiveness and remaining life. Even though non-destructive evaluation technologies have improved significantly, visual inspection is still a main tool used to assess the condition of structures, especially bridges. This research investigates the use of laser scanners coupled with images as a tool for improving the current visual inspection strategies. Laser scanning capabilities have advanced in recent years and have gained more recognition as a tool for applications in numerous fields. It is now possible to collect millions of texture-mapped data points that are accurate to within millimeters. In this work, captured texture-mapped datasets are processed using several damage detection strategies, which integrate existing condition rating criteria for a wide range of damage types, in order to locate, quantify and document the surface damage. These damage detection strategies include methods developed for detecting both element and surface damage that are present on the investigated structures. In order to show that defect localization, quantification, and documentation are performed successfully, the proposed methods are used to process the texture-mapped 3D point cloud collected from test-bed bridges. The investigated test-bed bridges include a range of element and surface damage that includes cracks, spalled concrete regions, steel section loss, delamination, and corrosion. The obtained results show that texture-mapped 3D point clouds may be used effectively to detect and document quantitative information on present conditions of bridges.

RABIT (Robotics Assisted Bridge Inspection Tool) provides rapid and automated condition assessment of concrete bridge decks using multiple nondestructive evaluation (NDE) technologies integrated into a robotic platform. In particular, the system is designed to characterize three most common deterioration types in concrete bridge decks: rebar corrosion, delamination, and concrete degradation. For that purpose, the system uses four technologies: electrical resistivity (ER), impact echo (IE), ground-penetrating radar (GPR), and ultrasonic surface waves (USW). In addition, the RABIT has two cameras for high resolution bridge deck imaging to provide a permanent record of the visible deterioration and surface features. The autonomous data collection is complemented by an advanced data analysis, interpretation and visualization. The most of the data analysis is conducted in real or near real time. The results are presented in terms of condition maps and condition indices. The data visualization platform facilitates an intuitive 3-dimensional presentation of the main three deterioration types and deck surface features. The data collection, analysis, and results presentation by the RABIT system are described and illustrated.

Weathering steel is commonly used as a cost-effective alternative for bridge superstructures, as the costs and environmental impacts associated with the maintenance/replacement of paint coatings are theoretically eliminated. The performance of weathering steel depends on the proper formation of a surface patina, which consists of a dense layer of corrosion product used to protect the steel from further atmospheric corrosion. However, the development of the weathering steel patina may be hindered by environmental factors such as humid environments, wetting/drying cycles, sheltering, exposure to de-icing chlorides, and design details that permit water to pond on steel surfaces. Early detection of deleterious corrosion is important to extending the service life of the bridge structure; however, established inspection procedures for weathering steel bridges are often not available to inspectors. This project assessed different inspection and testing techniques in order to evaluate the performance of the patina and/or the level of chloride contamination. A combination of visual inspection and tape testing was found to be the most practical and cost effective inspection methods that achieved objective, reliable and repeatable results. This study also developed a patina rating index for comparison of performance between different inspection cycles or between various bridges within an inventory. The patina rating index can also be used to prioritize general maintenance needs for a weathering steel bridge inventory.

With the volume of aging bridges approaching the end of their service lives nationwide, maintenance of these deteriorated structures is a growing challenge for transportation agencies. To manage this infrastructure, inspectors are tasked with providing an average rating based on element-level condition measurements. According to the National Bridge Inspection Standards (NBIS), many of the proposed inspection methods are visual and as a result, the evaluated condition states are generally qualitative and in most cases based on engineering judgments. To combat this issue, agencies have begun to utilize a variety of technologies to monitor the behavior and detect different sources of damage in the bridges and generate higher fidelity condition metrics. These condition metrics are used in the load rating process, which mainly focuses on the behavior of degraded elements to assess the remaining capacity of the bridge system. However in these practices, less attention is attributed to the overall system-level response under the reported condition states. An appropriate understanding of in-service performance requires knowledge of characterizing the influence of damage and deterioration on the overall system behavior. Today’s computational capabilities provide a tool to assess these characteristics using numerical and theoretical models representing the bridge structural system. Moreover, recent advances in monitoring and inspection techniques provide a mechanism to efficiently capture the damage data necessary for model updating. Using non-linear FE analysis, this paper presents a case study on evaluating the behavior of representative in-service bridges in the Commonwealth of Virginia, under the effect of deteriorating conditions. The geometrical characteristics of the selected structures represent common features of steel-concrete composite bridges serving within the state. The range of the corresponding damage characteristics were also selected through a questionnaire which collected inspection data from the VDOT engineers in nine different districts across the state.

The U.S. currently spends tens of billions of dollars annually to inspect infrastructures and collect subjective, qualitative data that can often be unreliable or largely irrelevant. Inspections also require adequate access to remote locations, for example, appropriate scaffolding, lifting and additional protective equipment, which might increase the associated personal safety risk and add costs. The use of unmanned vehicles has experienced a tremendous growth primarily in military and homeland security applications. However, it is a matter of time until Unmanned Aerial Systems (UAS) will be widely accepted as platforms for implementing monitoring and inspection procedures. Researchers at Drexel University are exploring the use of quadcopters as vehicles to carry a set of remote sensors with the ultimate goal to perform bridge condition assessment. While the accuracy of remote sensing systems is somewhat limited compared to the one of contact sensing systems, the ability to quickly and periodically scan/inspect a structure without the need for scaffolding, ropes, or cherry pickers currently used during bridge inspections could transform the way the industry performs periodic bridge inspections. The Drexel team owns a number of UAS with different payload, flight time and range capabilities. In this paper, recent results obtained from preliminary testing on small mock-up concrete bridge decks as well as on small/medium size bridges are presented. One of the main efforts is to explore how multispectral imaging can provide a preliminary assessment of the deck condition of common highway bridges. Among future goals, Drexel’s team plans to develop and validate computer vision approaches leveraging data collected using UAS to permit geometric characterization (quantification of bearing position, girder deformations) and condition assessment (e.g. quantification of spalling and corrosion areas).

This paper describes Louisiana’s new and innovative approach to prioritizing rehabilitation efforts for the state’s population of 4,500 bridges. Historic bridges were identified and selected for preservation on the state or local system based on their condition, function, and rehabilitation potential. The project outcome focuses the state’s efforts on bridges that can thrive into the future and are important to community and engineering heritage. With guidance from consultants at Mead & Hunt, the Louisiana Department of Transportation and Development (LADOTD) and project partners narrowed the focus to 150 historic bridges. The results positively affect bridge owners and consultants in the state by streamlining 97% of bridge projects and providing clear direction on how to progress with the 3% of bridges that are historically significant. Applying an innovative approach that grades bridges based on their condition, function, and rehabilitation potential, each historic bridge was categorized for future treatment as follows:

Replicable procedures—The Condition Score metric developed for this methodology can be replicated for use by other states with a similar need to set priorities for historic bridges. The score measures a bridge’s geometry, structural capacity, and other safety factors that impact its suitability for continued vehicular use. It is a good predictor of potential for long-term preservation and uses available inspection data, which is supplemented as needed.

The objective of this study is to establish and propose a hybrid data interpretation framework for automated performance monitoring of infrastructures. The framework is established by integrating non-parametric and model-based approaches. In fact, these approaches are merged in such a way that they can cover the associated drawbacks. The proposed framework consists of three main steps including analytical simulation of critical damage scenarios for a given structure, advanced statistical analysis and finally damage classification. In order to verify the efficiency of the proposed framework a 4-Span Bridge, is selected and exposed to the common damage scenarios. The framework has shown promising results in terms of continuous monitoring (detection the damage and classifying the critical abnormal behaviors).

A structure can be modeled using a multitude of methods, ranging from simple mathematical models with assumptions based on engineering judgment, to complex 3D models that attempt to capture every single variable that affects the behavior of the system. This paper, utilizing analysis of Rigid Frame Structures, explores different methods of modeling structures in an effort to understand the benefits, or lack thereof, of introducing more variables and complexity into a model. The focus is on a simplified method for the modeling of soil-structure interaction and analyzing a rigid frame structure. Through this effort it was found that, rather than use an expensive 3D modeling software, commonly available structural analysis software like LARSA can be used to create a simple soil-structure interaction model. This simple method allowed us to quickly create numerous models to efficiently analyze different alternatives.

The Southington I-84 Eastbound and Westbound Bridges over Marion Avenue in Southington, Connecticut (Bridge Nos. 01235 and 01236) were replaced in 36 hours under CTDOT’s accelerated bridge construction program. Both superstructures were built offsite and moved into place using Self-Propelled Modular Transporters (SPMTs). Each bridge was instrumented and multiple finite element models of westbound bridge were developed in order to quantify the maximum allowable structural twist the bridge could tolerate during the SPMT move while ensuring resulting stresses would be below the allowable stresses. The change of support locations was analyzed in order to capture the states of stress resulting from the differing support conditions at different construction stages. This included simply supported end conditions on the temporary towers to cantilevered end conditions on the SPMT’s. Additionally, four different deflection cases were analyzed at each SPMT support corner in order to represent a worst case scenario of a local loss of support during the bridge move.

Over the past decades moderate/severe earthquakes often caused great damage to bridge decks due to their mutual collision and large residual deck offset due to yielding in the traditional steel restrainers. This issue raises a need of developing a smart expansion joint with a high recentering strength to prevent decks from collision and to restore the original configuration. Buckling restrained SMA can provide a much higher recentering strength than unconfined SMA (approximately 1.2 ~ 1.5 times), which significantly reduces the amount of SMA and thereby the cost of the smart expansion joint proposed herein. The other important feature is that the proposed recentering mechanism always causes the confined SMA compressive, rather than tensile, when the expansion joint is in either tension or compression. This innovative recentering mechanism eliminates the issue of SMA’s break due to tensile strain limitation (approximately 0.12 strain). To verify the proposed buckling-restrained SMA symmetrical expansion joint, an individual recentering bucking restrained SMA device was quasi-statically tested in a uniaxial MTS 810 testing machine. The observed hysteresis of the device under cyclic loading shows high strength symmetrical tension/compression loops, together with a relative large ductility. The obtained experimental results were used to calibrate a confined SMA model in OpenSees. Finally, a three-span simply supported steel bridge with the proposed buckling restrained SMA expansion joints that have a high recentering tension/compression strength was numerically investigated using incremental dynamic analysis. The results reveal the high recentering ability of the bridge.

Preservative treated timber bridges have a long history of providing creative and sustainable design options for engineers, for railroad, vehicle and pedestrian traffic. The use of preserved wood for maintenance and construction of pedestrian, highway and railway bridges over aquatic and wetland environments has long been the material of choice for these applications due to the economical cost of material, minimal environmental impacts when managed and a strong performance track record. The full benefits of using preserved wood products can best be achieved when site specific project risks are properly evaluated; applicable mitigating measures are utilized to minimize and manage potential risk; the appropriate preservative is selected for the intended application; and the material is properly installed and maintained. When these measures are properly considered on a project basis, there is a high probability the preserved material will have a long service life and the potential risks will be minimal and manageable for environmentally safe use.

In performance based seismic design of structures, estimating the equivalent viscous damping (EVD) using a damping-ductility relationship is a major step. The seismic response of Shape Memory Alloy (SMA) reinforced concrete (RC) bridge pier is different from its traditional steel reinforced or post-tensioned counterparts. Due to its significantly different hysteretic response and material properties, it is necessary to estimate the EVD of SMA-RC pier and establish the damping-ductility relationship. An error in the estimation of equivalent viscous damping can lead to significant errors in the ductility demand of the designed pier. This study aims to develop expressions for equivalent viscous damping and damping-ductility relationship for SMA reinforced bridge pier when SMA rebars are used in the plastic hinge region of the bridge pier. New equivalent damping relations for five different bridge piers reinforced with five different types of SMAs have been developed. Nonlinear dynamic time history analyses were conducted on five different SMA-RC bridge piers using 100 ground motions. The accuracy of the new equivalent damping relation was assessed to ensure the applicability of the proposed relationships. Finally, a general expression was developed that can assist in estimating equivalent viscous damping for performance based seismic design of SMA reinforced bridge pier.

The bridge seismic retrofit measure presented in this paper aims to concentrate all the inelastic demand and energy dissipation, during a moderate to large earthquake, in disposable elements while the main structure remains essentially elastic and its integrity is preserved. Buckling restrained brace (BRB) systems have been successfully implemented in buildings; however, their implementation in bridges has been limited. The design implementation of BRBs that is presented include the analysis of the overall behavior of the bridge under two seismic performance levels and outlines design options for the brace-to-concrete connection. A case study of a representative reinforced concrete bridge bent constructed in the 1950 to mid-1970 in the Pacific Northwest is presented in an effort to demonstrate the retrofit procedure for the transverse direction. This retrofit option provides an additional tool for bridge design professionals looking to comply with performance-based criteria used to assess typical retrofit options.

In this paper, a direct displacement-based seismic design method for the hybrid sliding-rocking (HSR) segmental bridge piers is presented. The HSR bridges consist of unbonded post-tensioning, end rocking joints and intermediate sliding joints (or slip-dominant joints) along the column height. Joint sliding provides energy dissipation with small damage and control of the applied seismic loading. Residual joint sliding is small and restorable after an intense earthquake event. Force-based seismic design of the HSR columns is difficult to apply because representative R-factors are not available and are difficult to estimate. For this reason, displacement-based design methods are investigated. The proposed method involves an iterative scheme that builds on the capacity spectrum method. In the proposed method, a pushover curve for the HSR columns is computed analytically. Then, the equivalent viscous damping ratio is computed as function of the column displacement. Eventually, the spectral demand obtained from the FEMA 356 is compared to the spectral capacity obtained from the pushover curve are compared. The computed performance is compared with intended performance objectives and iterations are conducted to obtain economical designs. A preliminary comparison of the proposed design method with the results of an experimental study is presented.

Project-specific earthquake ground motions are developed for design of the Sixth Street Viaduct replacement project in Los Angeles, California. The replacement bridge, selected as a result of a design competition, is a twelve span tied-arch structure nearly 1 km in length, with a friction-pendulum base isolation system to mitigate high seismic loading. Following state of the art procedures used on recent major toll bridge projects in California, the design ground motions are developed by: performing seismic hazard analysis to develop target rock response spectra at two performance levels (100-yr and 1000-yr return period); selecting ten sets of seed motion time histories based on the controlling source information (3 sets for 100-yr and 7 sets for 1000-yr); performing spectrum matching to the target rock spectra; conducting free field site response analysis to develop depth-varying motions at each support location; and performing pile-soil interaction time history analyses to develop kinematic motions for each bridge support. To develop the target rock motion spectra, comparisons are made between seismic hazard analyses conducted using the widely adopted NGA-West1 and the newly released NGA-West2 relationships, as well as procedures recommended by the California Department of Transportation (Caltrans). Long period motion, beyond the range of typical applications (T of up to 10 seconds), is also addressed due to the friction-pendulum base isolation system. Since the friction-pendulum bearing size is determined based on non-linear time history analyses, careful consideration is given to the cross correlation of the two component horizontal design acceleration time histories. This helps to minimize unintentional over or undershoot in shaking in directions other than the two orthogonal axes for which the reference rock motions are developed.

Pile driving may affect adjacent and remote structures and their contents susceptible to vibrations. Therefore, it is important to evaluate expected vibrations prior to pile installation. A scaled-distance equation is the simplest and wide spread approach for calculating of the maximum velocity of ground vibrations prior to the beginning of production pile driving. This equation provides assessment of ground vibrations as a function of mostly the hammer energy and the distance from a driven pile. A choice of an appropriate distance and effects of the hammer energy together with other factors on ground vibrations are analyzed. Advantages and disadvantages of a scaled-distance equation are demonstrated.

The ability to accurately and rapidly assess structural integrity after a disaster is critical from both a safety and economic perspective. Existing post-disaster inspection methods are time-consuming and expensive, requiring highly trained inspectors to travel to target sites and manually collect data. Automated analysis of civil structures from visual data through computer vision can be used to improve the level of accuracy in the condition assessment procedure. This paper presents a method of automated and systematic computer vision-based structural analysis. It uses a set of digital photographs to produce a 3D model through Structure from Motion (SfM) algorithms, followed by fully automated recognition and assembly of structural elements (e.g., columns and beams) from the image-based 3D dense reconstruction of the structure. There are three key challenges in this work: (i) proper 3D mesh segmentation, (ii) robust computer vision algorithms for isolating different structural components, and (iii) classification and localization of damage that is present in the 3D model. As the part of the proposed system, extracted information from the dense 3D model is used to assemble the structural elements and create a Finite-Element Method (FEM) model. Lastly, a supervised machine learning scheme built upon a large and comprehensive data set is used to automatically update the model to account for damage. The proposed methodology has applications beyond post-disaster condition assessment, from routine inspection to infrastructure management applications.

This paper presents experimental investigation for the seismic performance of two half-scale fully prefabricated multi-column bridge piers under the cyclic quasi-static loading. The first specimen incorporates emulative monolithic connections between the precast members. This solution is called “High-Damage”. This solution achieved similar seismic performance levels and ductility (such as formation of plastic hinging), as that can be expected of a monolithic construction. However, residual displacement and significant structural damage at the plastic hinging zone would require extensive repair work and possible replacement of the bridge after a big earthquake. The second specimen is a “Low-Damage” solution. The specimen incorporated unbonded post-tensioning with the external dissipaters for a superior seismic performance. This solution eliminates any type of damage to the substructure components with full re-centering of the bridge following a big earthquake. The paper further provides a comparison of the High-Damage and Low-Damage solutions.

Integral abutment bridges (IABs) can result in decreased construction and maintenance costs, but certain aspects of their structural behavior are still not well understood. Most IAB research has related to the behavior of their substructures, with the limit states considered by entities such as the Illinois Department of Transportation (IDOT) largely based on substructure considerations. It is expected that integral abutment construction also affects superstructure behavior and demands, in addition to superstructure properties directly influencing substructure behavior. As a result, IDOT and the Illinois Tollway have sponsored a research project, investigating IAB behavior as it relates to bridge superstructures. The overall goal of the research is to improve design and construction provisions and details for IABs, so that actual in-service demands are more rigorously considered and IABs are efficiently used. The research project is employing a detailed suite of parametric numerical simulations, complemented by thorough field monitoring of two IABs located in northern Illinois. This paper presents findings from: 1) a subset of the numerical simulations, where effects of parameters such as abutment skew, overall bridge length, intermediate span length, and bridge width are examined; and 2) preliminary field data from the monitored bridges for the first complete summer-to-winter temperature cycle. An initial assessment of the key response quantities of longitudinal bridge displacement, thermally-induced elastic stresses in the superstructure, and inelastic pile strains are presented.

Performance based seismic design has emerged as one of the most rational methods to overcome inherent risks and uncertainties in predicting the seismic performance of structures designed by the force based approach. The Vancouver Evergreen Line Rapid Transit Project is a first known rapid transit project in Canada utilizing the multi-level performance-based design approach for the Guideway structures. The proposed Guideway alignment runs through enormously challenging site conditions prone to soil liquefaction causing variable, large-scale lateral spreading. Ground improvements were mostly precluded due to deep liquefiable layers coupled with a stiff crest near the surface, utility proximity and right of way issues. Innovative and robust structural solutions had to be developed to meet the performance criteria. Non-linear structural analyses incorporating soil-pile-structural interactions and directional ground deformations were carried out to confirm structural performance. As per the Project Agreement, the station building structures were designed based on the single-level and force-based design approach of the 2006 British Columbia Building Code, which presented additional challenges for the interface structural elements. This paper provides a summary of the seismic design criteria specified by the PA, seismic design review and approval process, technical challenges faced and innovative design solutions developed to meet the prescribed seismic performance criteria.

This paper presents the behavior of precast hollow-core fiber reinforced polymer (FRP)-concrete-steel tubular columns (HC-FCS) under combined axial and lateral loading. The HC-FCS column consisted of a concrete wall sandwiched between an outer FRP tube and an inner steel tube. Two large scale columns, RC-column and HC-FCS column were investigated during this study. The steel tube of the HC-FCS column was embedded into the footing while the FRP tube was stopped at the top of the footing level, i.e., the FRP tube provided confinement only. The hollow steel tube is the only reinforcement for shear and flexure inside the HC-FCS column. The FRP in HC-FCS ruptured at lateral drift of 15.2% while the RC-column displayed 10.9% lateral drift at failure. The RC-column failed due to rebar rupture and the moment capacity suddenly dropped more than 20% after that. However, the HC-FCS suffered gradual failure due to concrete crushing, steel local buckling and yielding, followed by FRP rupture.

Seismic base isolation is one of the most efficient ways to protect structures (e.g. buildings or bridges) from disastrous effects of earthquakes. Base-isolated structures are mostly being designed and constructed in developed countries such as United States, Italy, Japan, and New Zealand. In order to extend such applications to developing countries, new techniques are introduced by reducing the cost and improving the performance of earthquake protective systems. In this regard, advanced materials such as shape memory alloys (SMA) are implemented into base isolation mechanisms (e.g. elastomeric bearings) and efficient manufacturing processes are developed. When a new generation of smart elastomeric isolator is introduced, it is critical to assess its seismic performance under different ground motions. The goal of this study is to evaluate the seismic fragility of a multi-span continuous steel-girder bridge isolated by SMA wire-based natural rubber bearings (SMA-NRBs). Results show that equipping natural rubber bearing (NRB) with SMA wires decreases the probability of damage of the bridge. It means that the bridge system becomes less fragile when NRB is fitted with SMA wires.

Over the last decade, unmanned aerial systems (UAS) technology has matured to the point that it is now a viable option for augmenting more traditional bridge inspection methods. Any UAS-based inspection must address questions regarding the design of the aerial platform, the choice of on-board inspection cameras, and the protocols for the human pilot to follow. The wide variety of currently available UASs and imaging systems, as well as a current lack of UAS inspection standards, can pose challenges to engineers attempting to design or test a new system. The Placer River Trail Bridge, located on the Alaskan Kenai Peninsula, has been chosen as a test site for the prototyping and testing of a new UAS bridge inspection system. The desired final inspection product guided the design and operation of the UAS. The research team emphasized a data-driven approach in developing the UAS and its associated inspection protocols. Goals included providing high-resolution scans of the bridge capable of detecting a variety of damage indicators, and producing a 3D virtual model of the bridge using Structure-from-Motion. The resulting designs of both the UAS and the inspection protocols are presented herein. The results indicate that such a data-driven approach can lead to UAS inspection systems that are more capable of meeting the needs of bridge asset managers and inspectors.

A four story, 22,200 m² (239,000 ft²) wood light-framed assisted-living residential structure was examined for the causes of multiple alleged construction and design defects. The structure was framed using certain “advanced framing” techniques. Observed defects included uneven floors, window and door operation problems, misaligned I-joists and detailing problems with the building envelope. Alleged design defects related to structural engineering included wood shrinkage, uneven and excessive settlement and inadequate design documents. We discuss our approach and methods towards the investigation, including steps taken to ensure fairness in our examination. We present the possible defects in design and construction that we discovered which were easily preventable. We will present recommendations for practicing design professionals and code officials including:

Conclusions and recommendations can be applied to any light-framed wood structure but are particularly applicable to buildings in North America. Designers and Code Officials should gain a better understanding of the problems and solutions for complex, light, wood-framed structures. Wood construction can be quality construction with the right approach!

The Manhattan West North-East tower is a high rise office building located in Midtown Manhattan, New York City, one of densest and busiest business hubs in North America, and part of a larger parcel of land encompassing extensive areas of active railroad tracks. The rapid growth in this area necessitated the development of engineering designs and construction methods that could enable building over tracks and exploiting air space. In this particular case, a creative engineering solution has been implemented in order to kick the majority of the perimeter columns back to the concrete core, and therefore avoid the existing train traffic running below. This paper will delve into the challenges and specifics of this innovative structural system and all the related design optimizations. The 35 Hudson Yards is a 71 story mixed-use building located over the railroad yard below at the southeast corner of 33rd Street and 11th Avenue in Midtown Manhattan, New York City. The building height is approximately 1010 feet above the Platform level and an additional 35 feet above the railroad tracks. 35 Hudson Yards as a point tower incorporates 1.05 million square feet of mixed-use program consisting of retail, health club, office, hotel, and residential. Above the railroad tracks at roughly the elevation of the surrounding streets, a structural steel Platform will be constructed to cover the tracks and to support the Tower above. The Platform supporting columns and walls have been located between the railroad tracks using specified clearances required by Amtrak and MTA guidelines. Typical spacing of vertical supports to which the tower core wall and perimeter columns are aligned and transferred is approximately 50 feet in the north-south direction. Caissons supporting the vertical platform columns and walls will be drilled into bedrock throughout much of the site. The tower above consists of a reinforced concrete core wall system supplemented by buttress walls from the core out to the perimeter. Four (4) reinforced concrete buttress walls in the north-south direction and two (2) reinforced concrete buttress walls in the east-west direction extended from the core wall system out to the perimeter of the building. In addition, concrete belt walls at three levels are utilized to resist lateral loads. The floor framing system for office, hotel and residential consists of reinforced concrete flat plate supported by perimeter reinforced concrete columns and core/buttress walls. The design of tall buildings over the railroad yard requires not only structural design challenge for the design team but also provides significant opportunity converting air rights to build tall buildings in New York City.

The 2-day cycle is commonly used in New York City for residential concrete projects. Given that a floor is poured every other day, instant communication and in-field coordination are key to maintain the fast paced schedule and minimize mistakes. The structural engineer needs to be fully immersed in the day-to-day construction process to ensure successful and timely completion of the project. A case study of a 600,000 square feet residential concrete flat plate building will be presented to illustrate the construction process in a 2-day cycle. The typical floor plate consisted of 58 apartments with an average floor area of 700 square feet per apartment, which resulted in congestion of mechanical, electrical, and plumbing (MEP) components. As detailed coordination of the MEP trades occurred during construction, the structural engineer played a crucial role in ensuring that the placement of conduits and risers did not compromise the capacity and the integrity of the structure. Though ACI-318 provides some guidance on how to address embedded conduits and slab openings adjacent to columns and walls, the provisions were found to be insufficient when dealing with the complexities and constraints present in the project. The construction team communicated directly with the structural engineer, but a formal submittal and RFI process was also put in place for record keeping and to keep all parties informed. The case study will illustrate the common coordination problems that occur in the field, where they are likely to happen, and strategies to minimize these problems in future projects. The presentation is targeted towards structural engineers involved in building design and construction of reinforced concrete buildings. The case study and construction practices presented are from the New York City region but the ideas presented are applicable to other parts of the country. Through examination of the lessons learned, the audience can better identify potential coordination and communication issues in future projects and resolve them quickly as they arise.

When designing wood-framed structures engineers tend to visualize buildings as idealized structures. However, real world construction practices tend to produce results that sometimes stray from what the design engineer had in mind. This paper presents examples from a career in forensic investigations of existing buildings, where construction practices, although technically not in violation of the code, have been consistently found to produce installations that may be less than what the design engineer intended. Examples are given broken into sub-categories of horizontal diaphragms, shear wall construction, shear transfers, and foundation anchorage. These examples are accompanies by exemplary photographs of real-life installations. The information would be of particular interest to young engineers learning their craft, as well as to engineers involved in the design of wood structures.

Crowd behavior during Lively Concerts and sporting events may excite the supporting structures. Even more extreme, Exercise Concerts (similar to a Zumba® Fitness Concert) can have music beats approaching 3 Hz, or 180 beats per minute. This frequency range is likely to exceed the rhythmic activity design parameters typically assumed by designers. Owners and facility operators may be concerned about the life safety and comfort of patrons engaged in such activities. On a recent project, we investigated an existing structure for crowd induced dynamic loading from a “Fitness Concert” for an owner. The project involved a floor structure comprising existing precast double-tee beams supported on inverted tee-girders. We conducted field measurements in order to verify the dynamic properties of the structural system. In order to do simple infield measurements of the floor structure, an iPhone was used to generate acceleration-time history data from an application using the phone’s built-in accelerometers. We verified the iPhone for this type of application with a simple test setup in the office. We used the field measurements with published analytical methods referencing the PCI Design Handbook, the National Building Code of Canada, and AISC Design Guide 11. We computed equivalent static loads (ESL) for a range of forcing frequencies to compare the dynamic loading with the design capacity of the precast double-tee. The study determined that the precast double-tee beams were suitable for typical concert crowd loads. However, the response from Exercise Concerts exceeded the typical human perception tolerance levels.

A segmental dome, 140 feet in diameter, rising 255 feet above grade, similar in size and shape to Brunelleschi’s Dome in Florence, caps the grand main library of the City of San Diego. Although similar in overall shape, the structure is quite different in material and system. The steel structure which comprises the dome is composed of eight ribs and eight sails suspended by a saddle shaped cable net on its exposed interior surface. It is constructed of 3000 individual members of steel weighing 285 tons.

Proper implementation of the International Existing Building Code (IEBC) is challenging for both traditional design professionals implementing rehabilitation or renovation projects, as well as engineers dealing with the repair and restoration of structures damaged to varying degrees by natural hazards, fire or other severe loading events. When buildings suffer damage, sometimes incongruent perspectives of owners, insurance representatives, design professionals, contractors and authorities having jurisdiction can further complicate already challenging conditions. In order to effectively achieve a fair and reasonable resolution based on sound technical and economic considerations, applicable building code provisions and related ordinances must be properly interpreted and applied. This paper, written from the structural engineer’s perspective provides insights - primarily via case studies - regarding the application of the IEBC provisions related to the repair of buildings that were damaged by a natural hazard, fire or other severe loading event. The case studies are preceded by a brief background of the development of the IEBC and a summary of general practices appropriate to the repairs of damaged structures. This general material is supplemented with three examples of damaged building investigations, each of which was selected to illustrate particular challenges. Specific provisions in the IEBC are discussed, coupled with the engineering and economic principles that must be considered in order to provide logical, code-compliant solutions that best serve all affected parties.

Steel concentrically-braced frames (CBFs) are used extensively as lateral-force-resisting systems for low to mid-rise buildings in moderate seismic regions of the United States, such as the East Coast and Midwest. CBFs are economical because they are stiff, strong, and relatively simple to design, fabricate, and erect. Although good structural performance of CBFs for typical gravity and wind loading is well-established, there is little evidence—either from experimental research or field observation—related to CBF performance when subjected to design-basis earthquake demands. CBFs in moderate seismic regions are often not specifically detailed to achieve ductile inelastic response, so the effect of brittle limit states is largely unknown. As a result of this situation, a research project was initiated to investigate the seismic performance of CBFs in moderate seismic regions. This paper summarizes one aspect of the project: a full-scale cyclic test of a one-bay two-story Ordinary Concentrically Braced Frame—focusing on the sequence of limit states and associated system behavior. The test frame exhibited ductile response characterized by brace compression buckling and tension yielding up to nearly 1.5% frame drift and then experienced sudden strength loss due to weld fractures.

Many of the greatest structural artists—designers practicing at the top of their profession and achieving excellence in efficiency, economy, and elegance of their structures—from Thomas Telford to John Roebling, from Othmar Ammann to Fazlur Khan, practice primarily in the media of iron and steel. During the latter part of the 20^th century and into the 21^st century a handful of designers have carried on this tradition of greatness in structural art in metal. This paper sets the context for modern works of structural art in metal through a brief examination of the history of great design in metal and then examines Jörg Schlaich as an exemplary modern practitioner of the art form through a sequence of bridge and roof structures that cover the period from roughly the 1980s to the present and range in scale from modest pedestrian bridges to long span roofs for major places of public assembly. These structures are examined in terms of their structural efficiency, economy, and elegance. Elegance is interpreted here to entail ways in which the designs spring from creativity constrained by the requirements of good structural engineering; the degree to which the designs are innovative and introduce new techniques or ideas to the discipline of structural engineering; and, whether and how the designs are visually expressive of their structural function. Although impossible to quantify, the aesthetic beauty of the structures is also considered. The works of Santiago Calatrava are compared to those of Schlaich as a coda to the paper to spur greater discussion of the meaning of excellence in structural design.

Winters with heavy snow are often tough on older buildings throughout the northern United States. Although the measured snow loads rarely exceed Code design requirements, buildings sometimes fail and others develop performance problems under snow loads. Among the myriad problems we have investigated, several involve wood-frame houses common to older northeast cities and towns, including many that date from 1900 through the 1920s. In addition to these older structures, we have observed significant problems in newer houses associated with the post-World-War-II building boom. Both of these building types are wood-frame and non-engineered. They are typically built to standards that were not codified, but simply handed down from one generation of framers to the next. This paper and its accompanying presentation will describe the behavior of wood-frame roof structures under heavy snow load. This includes examples of failure modes and discussion of strategies for repairing and strengthening the resultant damaged buildings, or reinforcing them ahead of time to prevent problems. The architecture of ranch houses has changed relatively little over the decades since the post-war building boom. Further, building codes now govern their design and construction. However, many houses built well after the adoption of model building codes deviate very little from their predecessors. Undersized rafters, inadequate connections, and architectural deviations from established norms all contribute to problems in performance and an increased likelihood of failure. Although the Code includes explicit requirements for framing and connections, some of the Code requirements are not easily attained, and many are ignored.

Conceptualized in the late 1980s, the Bay Adelaide Centre is located in downtown Toronto and will eventually be home to 3.2-million square feet of commercial office space in three towers, with heights of 51, 45, and 33 storeys. Arriving at this milestone required, the use of innovative structural materials—this development features the world’s first high-rise constructed using 485 MPa (70 ksi) steel, North America’s first high-rise designed using 450 MPa (65 ksi) steel, and Toronto’s first high-rise constructed using 85 MPa (12 ksi) concrete in the core; teamwork—as with any multi-phase development, a number of development, design and construction professionals have touched this project; and patience—the project has been in design and construction for more than 25 years. Breaking new ground in the world of structural design takes more than shovels and hard hats. From this presentation, attendees hoping to bring structural innovations to their projects will learn what questions structural engineers should ask material producers; what questions they will have to answer for the owner, fellow designers and the construction team; and what other tools they should equip themselves with in order to enter smoothly into new territory. They will also get an idea of the efficiency that high-strength structural materials can bring to projects of varying sizes, as well as an understanding of the add-on effects of these savings—from logistics and fabrication, to cost.

While creativity has been specifically identified as a desired quality in the Engineer of 2020, creativity in and of itself is often “factored out” of most course activities since it is often perceived to run counter to traditional engineering pedagogy. Step-by-step methods that converge on a “right answer”, highly constrained class problems, and a rational aversion to risk not only limit opportunities for creative development, but also train students to eschew creative solutions or methods all together. This paper discusses where creativity—and specifically divergent thinking—is appropriate in design problems and describes design projects at various levels of the curriculum specifically developed to guide students from divergent idea generation to convergent final designs. These projects include a steel sculpture assignment from an Advanced Steel Design course used to review basic member design in an open-ended, creatively driven project.

Tilt is a steel and glass framed mechanism located on the 94th floor Observatory of the John Hancock Center in Chicago, IL. This unique “Patent Pending” structure consists of a movable platform that rotates about a horizontal axis to tip or “tilt” guests beyond the exterior face of the building for a thrilling view of the city below. Installing a moving system in this iconic landmark structure posed several challenges during the design and construction phases.

A land ownership agreement of neighboring properties necessitated the insertion of the new Utah Performing Arts Center under the entire southern portion of a proposed 25-story office tower. Based on an air-rights agreement, construction of the tower could exist above the 5-story performing arts center but no permanent support could reach the ground in the area of the facility. With unbalanced loads that would exist in the tower if some columns would reach the ground and the others not, the design team decided to balance all the loads of the tower and have no columns meet the ground. Located in a region of high seismicity, a performance based design of the reinforced concrete core wall and complex foundations define the structural system for the tower. Ductile link beams with high-strength concrete core walls are designed to resist all gravity and lateral loads with a three-dimensional steel roof truss system used to carry suspended perimeter column loads. Six friction pendulum structural bearings are used under the roof truss system to manage lateral and gravity load transfers at the top of the core walls as well as the change in temperature of the steel roof truss system. Advanced non-linear seismic analyses were performed on the structure along with a carefully conceived construction sequence using both permanent and temporary structural systems. The conceptual development of the design and analysis as well as the construction of this complex tower is presented.

Sometimes the familiar solution just does not cut it. This was the case in the design of a new art gallery constructed within the footprint of an existing 1930s apartment building for which Thornton Tomasetti (TT) performed structural engineering services. Zoning restrictions necessitated preservation of the existing exterior masonry walls. A steel skeleton was constructed within the building for bracing before removing the existing floors, and the steel was repurposed in the final composite steel/concrete frame system. Fully encased composite steel beams and columns, and concrete pan joists, were deemed best suited for the high design loads (as much as 300 psf), staged construction, and minimal structural floor depths. Thermally broken connections between the new interior framing and existing walls were required by the owner to optimize building performance. Additional structural innovations included the implementation of push piles to support the existing wall, the excavation of a new basement four feet beneath the existing foundations, a 10-foot thermally broken cantilever at the roof level, and the conversion of a portion of the building into a 40-foot high atrium. This paper will explore creative solutions and successful collaboration in demonstrating a successful model for combining structural system reuse, high performance structural design and detailing, and avant-garde architecture in one building.

The ASCE/SEI Technical Committee on Fire Protection was formed to support professional structural engineers conducting performance-based design of structural systems for fire effects with guidance documents. The Committee saw a need for an ASCE/SEI Standard 7 Appendix on fire effects on structures, and the authors led the development of a performance-based design method to support alternative approaches to prescriptive design methods. The use of performance-based design procedures for fire effects on structures is permitted by the alternative materials, design, and methods of construction provision in the building codes. The proposed Appendix fills a long-standing need within the industry to foster improved design and approval procedures for structural performance under fire conditions. The Appendix addresses fire, thermal, and structural topics that the structural engineer may need to understand or perform during a performance-based design, including general requirements, performance objectives, thermal analysis of fire effects, and structural analysis of fire effects.

Uncontrolled fire exposure represents a low-probability and potentially high-consequence event. The emerging field of structural fire engineering involves the explicit design of structural systems to adequately endure thermal load effects caused by uncontrolled fire exposure using rationally-allocated means of protection and potential modifications to preliminary structural system designs. Thermal load effects from fire exposure may include thermal expansion/contraction, reduced material stiffness and strength, and loads induced by thermal restraint. Under these conditions, it is critical that structural systems remain stable to fulfill required performance objectives. This paper examines requisite analysis tasks that precede the determination of structural response to fire exposure. Specifically, the determination of temperature histories of the structural system involves the following: quantification of the fuel loads, evaluation of structural design fires, and determination of the structure’s thermal response. The National Fire Protection Association (NFPA) has recently developed a standard that establishes a basis for selecting fuel load density and distribution. Also, the Society of Fire Protection Engineers (SFPE) has recently developed two standards that provide methods to determine time-dependent thermal boundary conditions on a structural system due to fire exposure, and the resulting thermal response of a structural system. Based upon the thermal response, the structural response to fire exposure may be determined.

Wind design provisions have changed dramatically since the publication of the 1988 edition of ASCE 7: Minimum Design Loads for Buildings and Other Structures. This paper will compare the history of ASCE 7 wind design provisions from 1988 to 2010, and editions in between. Design examples will be utilized in order to show how changes in wind load provisions have altered the design of buildings in various areas of the United States. Civil and structural engineers should find this paper informative, and gain perspective on the history of ASCE 7.

In contrast to other naturally occurring loads such as wind-induced or earthquake loads, design snow loads are generally the result of a series of events that occur over an entire winter. As a result, a number of key variables are inherently generalized when developing standardized guidelines. While the ASCE 7 Standard is employed by engineers to define snow loading for structural design, a strict application of the standard is not necessarily synonymous with an optimized structural design due to these generalizations. The variability is increased further as building designs push the envelope in terms of geometry and energy performance. With improvements in design practice comes the need for refinement to the basis for loading derivation. Factors such as roof size, exposure, thermal capacity, and aerodynamics need to be considered when deriving loads. Design snow loads for roofs are typically considered as a fraction of the snow loading on the ground to account for the potential for snow that is drifted off of the roof surface. However, the potential for this loading relief decreases as the roof increases in size. The consideration given to area averaging effects when considering wind loading, as structural and cladding wind load components, is not realized when designing for snow loads. Wind directionality effects on the potential snow load distributions are also not accounted for. All step regions are treated as though there is an equal probability of occurrence of the loading magnitude. Further, with the exception of overheated structures such as greenhouses or unheated structures, the effects of thermal variations over a roof surface are not considered. However, variations to the internal operating temperatures and roof insulation values may lead to similar building performance characteristics. The use of alternative analysis tools including wind tunnel and finite area element modeling to determine the potential variability in design snow loads resulting from these factors is discussed and refinements to the current ASCE 7 snow load provisions that account for these factors are proposed.

This paper focuses on the effective mass calculations of an experimental and analytical research study in which two laboratory joist supported footbridge systems were tested with static and dynamic loadings. Effective mass of different modes in laboratory footbridges were measured through experimental modal analysis and compared to the theoretical and finite element model results. For both single span (30ft × 7ft; 9.14m × 2.13m) and three span (90 ft × 7 ft; 27.42m × 2.13m) footbridges, acceleration data was collected on three parallel lines in the longitudinal direction of the laboratory structures. Testing was done for different bottom chord extension configurations to observe the effect of the extensions on various properties. For effective mass calculations, the average mode shapes of the three longitudinal lines were used and one way systems were treated as beams. The mode shape vectors for the first bending mode of the single span footbridge and the first three bending modes of the three span footbridge were determined for each bottom chord extension configuration. Each mode shape vector was then normalized to establish the mode shape matrix, and the effective mass of the entire footbridge for each mode was calculated to be compared to the theoretical and finite element model results.

In major cities around the world, urbanization and rising land prices have been driving an increase in real estate development adjacent to, and above in many cases, railway lines and other transportation corridors. Structure-borne sound and vibrations from traffic can be are annoying to human occupants; if high, they can also be disruptive to operation of manufacturing facilities, medical facilities, and research laboratories. As awareness of structure-borne sound and vibration issues grow among owners, designers, and building occupants, there is a corresponding increase in demand for cost effective sound and vibration predictions and mitigation. This research describes the development and verification of an analytical model of vibration transmission in an existing four-story building in Boston that is based on the floor and column impedances where they are attached. Using geometric properties, the authors defined the dynamic behavior of the test structure in terms of column impedances (modeled as finite, wave propagating rods) and floor impedances (modeled as energy dissipating, infinite plates). Researchers performed impact hammer tests as means of verifying the floor impedances, and also collected shaker and train-induced vibration measurements near the test column. The authors highlight several aspects of this modeling approach, and discuss the effectiveness of using this approach to predict the vibration response of buildings subject to ground-borne vibrations.

A new deconstructable composite floor system consisting of precast concrete planks and deconstructable clamping connections is proposed to promote sustainable design of composite floor systems within steel buildings through comprehensive reuse of all key structural components. A pushout test setup has been developed to study the clamping connector behavior experimentally. Finite element analysis results are presented to investigate the strength and ductility of the deconstructable shear connectors and study the effects of the analysis parameters. The scope of the project also includes beam and diaphragm tests to study the flexural and in-plane behavior of the structural system.

Current design provisions for steel-concrete composite beams rely upon a strength-based approach as outlined by the AISC Specification. In partially composite beams, the headed stud anchors transferring interfacial shear between the concrete and steel can undergo significant slip, which is not accounted for directly in design. A numerical model was developed and benchmarked to calculate the flexural capacity of partially composite beams while accounting for slip at the steel-concrete interface. This paper presents the results of parametric studies that were conducted to evaluate the effects of various geometric and material parameters including percent composite action, beam length, and cross-section geometry. The calculated flexural capacities were compared with the corresponding nominal design strengths calculated using the AISC Specification. These comparisons indicated that longer composite beams with low degrees of composite action (of less than 50%) reached the shear connection capacity (i.e. shear connection ductility) before developing their nominal design strength as computed per the AISC Specification. This reveals the complex inter-relationship between the beam length, stud slip capacity, and the minimum level of partially composite action that may be permitted for design.

The composite slab is an integral part of typical steel frame construction, providing an efficient work platform and eventual floor for buildings. This collection of information provides a realistic picture of the composite slab and construction conditions with regard to structural integrity considerations. The information is based on a set of collaborative experimental tests intended to address the structural integrity of steel gravity frame structures. The typical role and construction of the composite slab is reviewed, followed by an overview of a variety of experimental test specimens. Considerations of the anchorage conditions of the slab and the bond between the concrete and metal deck are highlighted. The restraint and shrinkage cracking behavior observed in some of the specimens is also reported and compared to cracking that might be expected in typical construction. Possible areas of structural improvement in terms of robustness are noted.

Interaction of walking people with structures is known to be an important yet challenging when simulating vertical response of the structure due to walking excitation. Despite of its critical effects on structural response, no properly formulated and experimentally verified model exist to simulate effects of walking pedestrians on structures. In this work, a set of modal tests based on frequency response function (FRF) are done on a test structure with people walking in different loading scenarios. The occupied structure modal parameters found in these tests are used an identification procedure where ‘reverse engineering’ method is used to find parameters of walking individual’s single-degree-of-freedom mass-spring-damper model. A discrete model of human – structure system is used to simulate independent interaction of each walking person with structure. The analysis results suggest the ranges of 2.75 – 3.00 Hz and 27.5 % – 30% for natural frequency and damping ratio of SDOF walking human model respectively.

In recent years an evolution has been taking place with respect to improving thermal performance of buildings using continuous insulation with an air barrier to reduce energy costs as well as improving exterior cladding systems to resist water penetration using a so-called rain screen. However, a rain screen cladding assembly placed over thick continuous foam insulation presents construction challenges. The two main problems with the current conventional installation process are that: 1) during construction a lot of temporary fastener holes are created in order to temporarily hold the foam sheathing to the wall which then need to be filled with expanding spray foam creating subsequent expense, and 2) the layout and placement of the fasteners supporting the battens is “blind.” Locating the wall studs with blind fastening leads to missed studs and then another hole is created in the insulation and sheathing that needs to be filled and the fastener must be relocated to hit the framing. These shortcomings lead the authors to develop a new and unique prototype fastener. A new prototype fastener, termed the Impaler, provides the following benefits: 1) eliminates “blind” fastening i.e., allows direct to wood stud embedment, 2) provides an immediate supporting spike to “impale” foam sheathing and hold it onto the wall as a construction aid, and 3) provides a means of indexing to mark, drill, and then easily place battens. Lateral load testing of this new fastener shows its capacity is about 87 percent higher, on average, than similar tested assemblies using current conventional screws. The increased load capacity is likely attributable to several factors, which include added fixity due to the stop collar and end cap of the Impaler as well as its larger shank diameter.

This study assesses the environmental impacts of an archetypical contemporary 42-story residential concrete building designed to meet minimum code requirements and compares it to the impacts from a “beyond code” design. The earthquake performance of the building in terms of financial loss and repair time was previously evaluated using a FEMA P-58 based approach; this research used Life Cycle Assessment to estimate the environmental impact of both initial construction and seismic repair when the building is subjected to an earthquake with a 475-year return period. Three seismic force resisting configurations (fixed-base, base-isolated, and damped-outrigger) as well as two design approaches (minimum code equivalence and a resilience-based design approach) were considered. This study found that the magnitude of environmental impact of seismic damage repair can be significant; that the ratio of environmental impact to cost is higher for seismic repair than initial construction; and that the protection of non-structural components, such as partitions, can result in significant reduction in overall environmental impact of seismic damage when subjected to large earthquakes.

The Pertamina Energy Tower will be a 99 story office headquarters for the Indonesian state-owned energy company. Skidmore, Owings and Merrill is providing a holistic design solution that includes structural engineering, architectural design, and sustainability engineering. Part of a larger development that includes a performing arts and exhibition pavilion, a mosque, and a central energy plant, the tower will be the first super tall building in Indonesia. The primary goal of the project is to become the first campus with a supertall tower to achieve a net-zero energy performance, demonstrating a number of sustainable strategies. This complements the client’s goal of producing 25% of its overall energy portfolio from renewable resources. To achieve this goal, the project will incorporate numerous features to increase efficiency and generate on-site energy from solar, wind and geothermal sources. Additionally, the campus has a goal of “Zero Water Discharge” that is accomplished by examining the project as a whole and across all disciplines. The first component this goal is to reduce the required water through the use of efficient fixtures and systems. The second component is collection of water for reuse from alternative sources. Rainwater, grey water, black water, and condensate are collected, treated on-site, and reused to meet the campus water demands. The combination of these strategies reduces the campus potable water use by 66%, the overall sanitary discharge by 95%, and finally the stormwater runoff from the site by 100%. The structural design plays a crucial part of the sustainability strategy. High seismic forces combined with poor soil conditions require the use of a dual lateral load resisting system. The structural system is a ductile reinforced concrete core system coupled with a perimeter moment frame via outrigger and belt truss system at mechanical levels. Numerous optimization studies were undertaken to the mass of the building in order to reduce the seismic forces while retaining stiffness to control the building behavior under wind loads. The lack of local suppliers of high strength concrete and steel fabricators is a further imperative to reduce structural material in order to minimize transportation costs and energy.

The structural engineer designs members, provides connection details, and specifies material grades. The contractor bids on the project, orders materials, and constructs the structure. How is quality assured? How can the owner and structural engineer be confident that the provided details are properly constructed? The structural engineer performs observation several times during construction. The special inspector reviews specific materials and installations. The building inspector reviews for public safety. How can construction defects be mitigated? How can the quality of construction be maintained, and by whom? This paper will demonstrate how a lack of coordination, false expectations, and an overemphasis on cost and schedule can affect construction oversight quality and will provide recommendations for how team members can establish accountability, quality standards, and lines of communication. Furthermore, this paper will discuss effects of the emergence of the combined owner/builder entity and stresses from the economic cycle.

This paper will focus on aspects of the advanced analysis and underlying behavior of composite structures with concrete-filled steel tube (CFT) columns. Through a detailed examination of the results of a suite of full-scale slender CFT beam-column tests, insight into the cyclic behavior of such members is gained, specifically pertaining to local buckling of the steel tube and the plastic hinge length. Modeling techniques, which capture these behaviors, are introduced and incorporated into a general purpose distributed plasticity fiber based beam element formulation. The model is found to be capable of capturing the observed behavior and producing accurate results.

The anticipated performance of a 4-story reinforced concrete (RC) building designed in accordance with ASCE/SEI 7, is assessed using ASCE/SEI 41. Engineering practitioners employing the performance-based seismic engineering philosophy are increasingly using ASCE/SEI 41, as the “first generation” performance-based seismic design principle, to justify the adequacy of the seismic performance of new buildings. However, ASCE/SEI 41 was developed to assess the structural performance of existing buildings. In order to compare the anticipated structural performance between ASCE 7 and ASCE 41, the seismic performance of an ASCE/SEI 7 code-compliant 4-story special RC moment frame building is assessed based on the four evaluation methodologies defined in the Tier 3 analysis of ASCE/SEI 41 for the collapse prevention structural performance level. The assessment results show that the ASCE/SEI 7 code-compliant building does not meet the collapse prevention performance level requirements in ASCE/SEI 41 for the columns in the first story when linear analyses are employed.

The objective of this paper is to introduce several new and updated AISI standards for cold-formed steel structural design and explain how these standards provide an evolution for cold-formed steel towards the design of systems instead of isolated members and connections. Cold-formed steel members are used in a wide variety of applications and the historical approach of the AISI standards was primarily to support the design of individual members and steel-to-steel connections. However, as the use of cold-formed steel has expanded and matured it is now possible in several cases to reliably define cold-formed steel systems that are in common use. To support these systems, cold-formed steel framing, metal building secondary systems, steel diaphragm systems, etc. AISI standards now provide system specific design specifications and test standards. The evolution of these standards and the latest versions are explained herein. The focus of the discussion is on why the standards are provided, and how they aim to enable the cold-formed steel engineer, rather than on the specifics of each new edition of the standard. The base standard for all the system specific efforts: AISI S100 is also being reorganized and updated to accommodate new research and this new evolution in cold-formed steel system design. Significant work remains to fully develop cold-formed steel system design and evolve it further towards performance-based standards, but the new suite of AISI standards provides a robust foundation for this effort.

Cold-formed steel framed shear wall sheathed with corrugated steel sheets is a promising shear wall system for low- and mid-rise constructions at high wind and seismic zones due to its advantages of non-combustibility, high shear strength, and high shear stiffness. However, recent research showed that the shear walls using corrugated steel sheathing had brittle failure behaviors. This paper presents an experimental study aimed at improving the ductility of cold-formed steel shear walls by introducing openings and optimizing the configurations in the corrugated steel sheathing. A total of 11 sheathing configurations were investigated and 19 monotonic and cyclic full-scale shear wall tests were included in this project. The research discovered that with proper opening in the corrugated steel sheathing, the shear wall can yield significantly improved ductility while maintaining high-level shear strength and stiffness. Additionally, nonlinear dynamic analyses were also carried out to verify the advantages of the proposed innovative shear wall. The dynamic analyses show that the new shear wall system can greatly reduce the seismic effects and decrease the collapse probability of cold-formed steel buildings.

The design provisions for steel plate composite (SC) walls in safety related nuclear facilities are included in Appendix N9 of AISC N690s1 (AISC, 2015). AISC N690s1 is Supplement No. 1 to AISC N690-12 (AISC, 2012) specification for safety related steel structures in nuclear facilities and is due to be published in 2015. The design provisions include minimum requirements for SC composite walls designed using these provisions. These include minimum and maximum wall thickness and steel reinforcement ratio permitted. The provisions also include detailing requirements for SC wall sections. These include requirements for steel anchors for preventing local buckling before yielding, developing adequate composite action, and preventing interfacial shear failure. Requirements for tie bars between the steel plates (faceplates) are also provided to prevent splitting failure and out-of-plane shear failure. The provisions include design strength equations for axial tension, axial compression, out-of-plane shear, out-of-plane flexure, in-plane shear, and for combined in-plane forces and out-of-plane moment demands. The provisions also include interaction equations for evaluating tie bars resisting demands due to combination of out-of-plane and interfacial shear forces. The provisions include performance requirements for the anchorage of SC walls to concrete basemat, SC wall-to-wall connections and SC walls to floor slab connections. The provisions also include requirements for fabrication, inspection, and quality control of SC walls constructed for safety-related nuclear facilities. The outline of Appendix N9 will be discussed in the paper and the presentation. The paper will also discuss how the appendix can be utilized for the design of SC wall structures.

Concrete-filled steel tube (CFT) beam-columns are categorized as compact, noncompact or slender depending on the tube slenderness ratio (width-to-thickness b/t or D/t ratio, λ) and the slenderness limits (λ_p, λ_r, and λ_limit) specified by the AISC 360-10. The behavior and strength of CFT beam-columns depend on the tube slenderness ratio (λ), material strength ratio (F_y/f^’_c), axial load ratio (α) and member length-to-depth ratio (L/B or L/D). In previous articles, the authors have presented results of numerical investigations evaluating the effects of these four parameters, and developed P-M interaction equations for designing noncompact and slender CFT beam-columns. This paper evaluates the applicability of the developed design equations for: (i) designing compact CFT beam-columns, and (ii) estimating the available strengths of CFT members in frames designed using the direct analysis method. The applicability for designing compact CFT beam-columns is evaluated by comparing the P-M interaction curves resulting from the developed equations with those calculated using the plastic stress distribution method specified by AISC 360-10. The applicability for the direct analysis method is evaluated by comparing the available strengths estimated using the developed equations with demands calculated by conducting second-order elastic analysis using MASTAN2 (V3.3).

Steel plate composite (SC) wall piers are composed of two steel plates on both sides of a concrete infill. Composite action between the steel plates and concrete infill is achieved using shear connectors and tie bars. The tie bars also provide structural integrity by connecting the two steel plates together. SC wall piers do not have any flange walls, cross walls, or boundary elements. Their seismic response and lateral load capacity are governed by the in-plane flexural behavior and capacity of the SC wall cross-section at the base of the wall. The lateral load capacity is reached due to flexural failure in terms of: (i) concrete crushing of the concrete infill in compression, (ii) local buckling of the steel faceplates in compression, and (iii) rupture of the steel faceplates in tension. SC wall piers are composite alternatives to conventional reinforced concrete (RC) shear walls where the steel rebar curtains are replaced by steel faceplates on the exterior surfaces of the concrete walls. This approach expedites construction by eliminating the need for additional formwork and staging of concrete casting. This approach can also provide structural efficiency if the SC wall cross-section is detailed appropriately with adequate shear connectors and tie bars. These elements provide composite action and also restrain the steel faceplates from buckling prematurely (before yielding). Local buckling typically occurs between the base of the steel plates and the first row of shear connectors or ties, which makes this spacing important detailing criterion for SC wall piers. This paper will summarize the results from cyclic in-plane shear tests conducted on SC wall piers. Some of the cyclic lateral load-drift ratio responses are presented along with the typical hysteresis behavior and story drift capacity. Design equations for predicting the lateral load capacity of SC wall piers without boundary elements are compared with the test results.

This paper describes and illustrates the development and application of an alternate method of analysis along with explicit code design requirements used to evaluate two-way post-tensioned concrete floor slab punching shear for a number of as-built shear reinforcement conditions in an existing mid-rise resort hotel structure. The as-built conditions found by non-destructive testing verification as non-compliant with the design included headed stud reinforcement (studrails) installed with a shorter length than specified and studrails found missing or not in correct position at a number of columns. In order to efficiently evaluate punching shear at hundreds of unique slab-column connections to assure building code compliance and to also minimize costly and disruptive repairs at many locations with these conditions: (1) In-house analysis spreadsheet programs were developed based on punching shear design provisions of the ACI 318 Building Code Requirements for Structural Concrete and technical guides for all or some studrails missing from one side of a column; and (2) An alternative analysis approach was developed to take advantage of increased shear strength in prestressed slabs not currently codified by the ACI 318 Code but documented in the technical literature. This evaluation program substantially reduced the number of slab-column connections in the building that would have needed costly rehabilitation.

This paper describes modeling and analysis of a half-scale steel gravity frame system with composite concrete slab on steel deck that was constructed and tested at the University of Illinois under corner, edge, and interior column removal scenarios. For each scenario, distributed floor loading was incrementally increased until the floor system could not sustain additional load. The experimental results showed that the ultimate capacity of the floor system ranged from 44 % to 62 % of the applicable gravity load combination (1.2D + 0.5L), indicating a potential vulnerability to collapse. Analyses of the floor system used a component-based modeling approach for the shear connections, with load-displacement curves for each bolt row calibrated against experimental data from half-scale connections. Girders, beams, and columns were modeled with beam elements, and alternating strips of shell elements were used to represent the ribbed profile of the concrete slab on steel deck. The model accounted for partial continuity of the steel deck, as influenced by the actual placement of shear studs and spot welds. Blind pre-test predictions are compared with experimental data for the four column removal scenarios. The modeling approach was refined after each of the first two tests, and two factors were identified as having a significant influence on the response of the system: the post-ultimate softening modulus of concrete in tension and the out-of-plane (torsional and transverse shear) behavior of the shear connections.

Very limited full-scale experiments have been conducted to understand the mechanism of progressive collapse, which involves partial or complete collapse of a structure typically due to the loss of a vertical load carrying element(s). Progressive collapse design guidelines recommend simplified analysis procedures involving instantaneous removal of specified critical columns in a building. This research investigates the effectiveness of such commonly used methodologies by testing the vulnerability of an existing steel building on the Ohio State University campus. One first-story column was removed from the building to understand how the loads are redistributed. Deflections and strains within the neighboring beams and columns were measured during column removal. Experimental data from the field test were compared with data from structural analysis. The main conclusion is that more than 70% of the loads applied on the removed column are redistributed within the perimeter frame; the remaining loads are carried by the interior columns after the column is removed.

The overall goal of this research is to evaluate the potential of disproportionate collapse in older reinforced concrete flat-plate buildings subjected to the loss of a supporting column. If a supporting column experiences failure, then the load must be redistributed to the surrounding connections. If the punching shear resistance of the surrounding connections is not sufficient, then a progressive collapse may result. The research program considers dynamic testing of isolated slab column connections that represent the connection near the lost supporting column. The dynamic tests are compared to static tests of similar specimens to determine the possible strength increase in the connection due to the loading rate. The test results show that the dynamic loading can increase the ductility of the slab by 23%, but did not show any increase in the connection strength. In addition, one multi-panel specimen representing a 0.4 scale 9 column section of a flat slab building was dynamically tested. The specimen was loaded with dead weight equivalent to the design load 1.0D + 0.5L and an exterior column dynamically removed. No progressive collapse occurred in the flat plate structure.

Progressive collapse denotes a failure of a major portion of a structure that has been initiated by failure of a relatively small part of the structure such as failure of any vertical load carrying element (typically columns). Failure of large part of any structure will results in to substantial loss of human lives and natural resources. Therefore, it is important to prevent progressive collapse which is also known as disproportionate collapse. Now a days, there is increasing trend towards construction of buildings using precast concrete. In precast concrete construction, all the components of structures are produced in controlled environment and they are being connected appropriately at site. Connections are the most critical elements of any precast structure, because in past major collapse of precast structure took place because of connection failure. In this study, behavior of four different reduced 1/3^rd scaled precast specimens having wet and dry connections is investigated under column removal scenario and their performance is compared with monolithic connection. Precast specimens considered for the study are constructed by adopting different detailing having column with RC corbel and column with steel billet for connection with precast beam. Performance of specimen is evaluated on the basis of ultimate load carrying capacity, maximum deflection and deflection measured along the span of the beam. From the results, better performance of precast connections is observed up to elastic phase but later on strength of dry precast connections degrades more as compared to monolithic connection. Wet precast connections exhibit superior performance as compared to monolithic connection, which advocates replacement of monolithic connection with appropriate connection detailing. From the results, is also observed that precast connections constructed using RC corbel performs better as compared to those constructed using steel billet.

This paper presents a summary of an ongoing research studying framing strategies to increase the robustness in steel buildings by using stiff stories that can limit deformations capable of causing fracture and other undesirable limit states in cases of column loss. A catalog of buildings that incorporate stiff-story concepts is first presented. Buildings catalogued used the stiff-story concepts for architectural reasons or land space limitations rather than for increased robustness. Two buildings adapted from this catalog were further analyzed for column loss; the analysis and results for one building are presented. Linear static alternate path analyses according to the UFC 4-023-03 guidelines were performed and are presented. Nonlinear static analyses are in progress. Results from the linear static alternate path analysis showed that only five members were overstressed. However, only a few modifications were required to satisfy the UFC guidelines, proving the potential of the stiff-story solutions to resist column loss.

Current design guidelines for General Service Administration (GSA 2003 & 2013), United Facilities Criteria (UFC 2009) adopt the alternate path method for disproportionate collapse-resistant structures design. In the alternate path design approach, a critical structural component (typically a key column) is suddenly removed from the system and the ability of the other components of the structural system to withstand the added forces is examined. This can be done using linear or nonlinear static analysis (LSA and NSA) as well as the nonlinear dynamic analysis (NDA) method. In the dynamic method, the inertial forces are directly considered in the analysis through the equations of motion. However, a Load Increase Factor (LIF) is introduced in the static analysis methods to account for the modifications of dead and live loads due to the unaccounted for dynamic effects. The LIF value recommended by GSA (2003) is 2.0, while it is derived based on recommended equations adopted by GSA (2013) and UFC (2009). In this study, dynamic analyses of a multi-story building subjected to sudden column removal are conducted taking into consideration geometric nonlinearity and material inelasticity. Based on these analyses, the LIF is computed and compared with design recommendations. The results from this study indicate that the current values of LIF need to be re-evaluated in order to achieve more economical designs.

It has sometimes been presumed that the ability of buildings designed to resist seismic loading will inherently be superior to that of those designed for nonseismic conditions. This assertion is tested herein by comparing the resistance to progressive collapse of a series of representative moment frames. The assessments are undertaken using the alternate load path approach to sudden column loss, implemented by means of a technique developed at Imperial College London. The findings confirm that the greater moment capacity and rotational stiffness possessed by the arrangements used to provide the moment connections between the beams and the columns generally result in better performance. However, some features specifically adopted to improve seismic performance are found to be very poor in terms of their resistance to progressive collapse.

Recent large-scale tests have found that Steel Gravity Framing Systems (SGFSs) with conventional connections may not be adequate to support the specified gravity load combinations under column removal scenarios. To address this issue, detailed connection models were validated against experimental results and then used to investigate alternative gravity connection details to enhance the integrity of SGFSs. A procedure was developed to design new single plate shear connection details with multiple columns of bolts so that they had design shear capacities equal to or greater than corresponding conventional configurations. Analyses of the connections under column removal showed that improvements in both connection strength and deformation capacity can be achieved using the multi-bolt-column configurations.

The ability of a structure to accommodate the loss of a column has traditionally been referred to as its ability to resist “progressive collapse.” Recent guidelines, however, have begun to focus on the relative consequence or magnitude of the collapse rather than the manner in which it occurs, often referred to in industry as “disproportionate collapse.” This distinction is important as it allows for a structure to sustain localized failure, provided the resulting damage is proportionate to the initiating event and that it does not result in subsequent collapse and instability of the remaining structure. While designing structures to resist disproportionate collapse provides potential cost-savings, it requires accounting for structural debris in the collapsed area that may fall and impact floor levels below. This study presents a simplified approach for modeling the impact of falling debris on a structure below. An approach is presented to determine the initial conditions of a beam subjected to impact from falling debris utilizing basic principles of energy and engineering mechanics and the resulting response of the structure is evaluated using three simplified analysis methods. A design example is also presented for comparison and validation of each analysis approach.

This paper presents an overview of the issues associated with enhancing the resilience and robustness of the infrastructure. Key phenomena pertaining to global response and collapse resilience are described, and the kinds of results garnered from tests and issues associated with testing are mentioned. In this regard, deficiencies are described in the knowledge base related to the phenomena associated with the global response and failure modes of structural systems. Impediments to developing effective methodologies for specifically adding resilience to framing systems as part of their designs are also identified. Finally, the sorts of tests and testing setups that may be used to provide useful information are described.

The renovation of an existing office building to meet the progressive collapse requirements according to UFC4-023-03 is presented. The original building was composed of two structurally independent structures, both of which housed three indoor tennis courts. Both structures were column free in the interior and were constructed of built up wide flange perimeter columns and 6ft deep roof trusses for lateral and gravity load. A first building renovation transformed the original structure into two 3-story office buildings by adding a 2-story steel frame structure inside the original space. A second renovation added steel framing between the two buildings to create a single structure and provided support for a new cladding system. The office building relies on stair masonry walls for lateral support. Existing structural drawings were available only for the second renovation. In order to meet the UFC4-023-03 Progressive collapse guidelines, a system of hangers and ring beams was designed. In most cases the steel columns were used as hangers and their connections strengthened accordingly; in some cases rod hangers were provided. Ring beams were located at various levels depending on the column layout and additional blast retrofit requirements. In all cases, the ring beams were designed as continuous beams supported by the existing columns who behave as pins. This assumption results in heavier beams but avoids additional retrofit for the columns and the use of brittle and expensive moment connections. This paper presents details of the implemented retrofit as well as some of the challenges encountered during the design phase: the complexity of the geometry of the different structural systems, the definition of how many columns to be simultaneously removed and the applicability of the linear elastic method to the design of multiple elements of different ductility.

U.S. General Service Administration (GSA) published guidelines for the progressive collapse resistance of buildings in 2003 and 2013. There are significant changes introduced in the 2013 edition. The objective of this study was to compare the results of the progressive collapse analysis based on the 2003 and 2013 editions of GSA. For the purpose of the study, a 10-storey reinforced concrete frame building located in Vancouver, Canada was considered in the analysis. Progressive collapse analyses were conducted on a 3-D finite element model of the building in accordance with 2003 GSA and 2013 GSA, respectively. The differences between the two editions were also discussed in the paper, including the loads applied for the analysis and the acceptance criteria for the progressive collapse resistance. Finally, comments were made on the use of the 2013 GSA Guidelines.

This paper presents the application of a simplified approach for classification of bridges based on fire risk. An importance factor was developed for identifying the vulnerability of bridges to fire hazard. This importance factor, developed using weighted factor approach, takes into account the degree of vulnerability of different bridge components, critical nature of a bridge from traffic functionality point and fire mitigation strategies present in a specific bridge. This importance factor is applied for evaluating vulnerability of a typical bridge to fire hazard. It is shown through two case studies that the proposed importance factor can be used as a practical tool for identifying critical bridges from the point of fire hazard.

Applications of glass- and carbon-fiber reinforced polymers (FRPs) in construction have increased in recent years due to the deterioration of civil infrastructure and the numerous advantages of FRPs. Many advantages of conventional polymers and FRPs, however, are also disadvantages, especially when considering their environmental impact. The low cost of many polymers is an artifact of their inexpensive petrochemical feedstock, and their strength and chemical recalcitrance make them very difficult to degrade after their service life. This work concerns the development and characterization of sustainable, low-carbon alternatives to traditional FRP materials. Epoxy-like resins derived from animal proteins are combined with natural fibers to produce fully biobased FRP composites. Preliminary results demonstrate that these biobased FRPs exhibit similar mechanical properties to traditional FRPs. In this paper, the advantages and disadvantages of using natural FRPs in structural applications are discussed, along with the development of predictive models to facilitate novel materials design.

Seismic steel moment frames rely on the formation of plastic hinges at the beam ends and at the column bases to dissipate seismic input energy. Local buckling and accumulation of damage associated with this inelastic behavior may lead to inconsistent performance, residual deformation, and significant repair needs. To take advantage of the properties of light-weight, non-traditional materials that offer high damping, the integration of these materials into the hollow portion of hollow structural section members is considered to enhance their performance under large cyclic loads associated with a seismic event. The use of these materials as fill in hollow structural sections is explored through beam bending tests under cyclic load. The bending tests allow the cyclic behavior to be assessed with respect to fill material type (polymer foam and rubber), fill length, member width-thickness ratio, and member depth-thickness ratio. The results are used to evaluate the ability of the fill materials to control the behavior of structures during a seismic event and will benefit design professionals, code writers, and researchers in developing new ways to better integrate non-traditional materials into structural systems.

This study explores the development of an SMA-based self-centering viscous damper in order to mitigate dynamic response of structures subjected to multi-level seismic hazards and to enhance their post-earthquake functionality. The device, named as Superelastic Viscous Damper (SVD), exhibits both re-centering and energy-dissipating capabilities and consists of SMA bars and a viscoelastic (VE) damper. SMA elements are mainly used as re-centering unit and the viscoelastic damper is employed as energy dissipation unit. The VE damper consists of two layers of a high damped (HD) blended butyl elastomer compound chemically bonded to steel plates. Energy is dissipated through the shear deformation of elastomeric material by hysteretic damping. Experimental tests are conducted to characterize the behavior of both SMAs and elastomeric material and assess the influence of displacement amplitude and loading frequency on the material behavior. A parametric study is conducted to evaluate the effects of various design parameters of SVD on the overall behavior of the device. A prototype of the SVD is designed and fabricated. Results of the experimental tests on the prototype device show that a judiciously designed SVD can provide considerable amount of energy dissipation with almost excellent self-centering capability.

The objective of this paper is to provide a practitioner perspective on design and delivery of material innovations. The paper will introduce a wide set of issues, plus an illustrative case study, to consider in the review of specific structural material innovations. The issues will be presented within an evaluation framework, emphasizing drivers, barriers, and risks, and the structural engineer’s role in addressing these.

This paper studies the computational seismic response of two damage-resistant 20-story tall buildings, located at near-fault regions of strong earthquakes, with a reinforced concrete core-wall to provide the majority of lateral resistance above ground. The first building uses a post-tensioned core-wall designed to rock at the ground level resulting in minimal structural damage in the wall at the maximum considered earthquake (MCE) level of shaking. The second building combines an isolation plane at the base (below ground) of the building with a post-tensioned rocking core wall (dual-isolation system); the dual-isolation system results in minimal structural damage at the MCE level of shaking and reduces significantly demands to non-structural components. The three-dimensional seismic responses of the two buildings are compared to that of a conventionally designed core-wall building designed to develop a flexural plastic hinge in the core-wall. Nonlinear response history analysis is conducted using the two horizontal components of strong historical near fault ground motions. The three building models use a nonlinear beam-truss modeling scheme that explicitly accounts for flexure-shear interaction in RC walls and slabs.

Within the transportation community, steel is one of the most widely used construction materials; however, in most operating environments it corrodes, often resulting in a loss in capacity or serviceability. Fiber-reinforced polymers (FRP) have become a viable alternative to steel and continue to gain attention due to their high tensile strength and durability. To further the knowledge base of FRP, this paper focuses on the bond durability of unidirectional pultruded FRP bars—made with carbon (CFRP) and aramid (AFRP) fibers—in concrete after exposure to thermal fatigue and saltwater environments, for the purpose of understanding the performance of FRP for prestressing applications. Cube specimens containing AFRP, CFRP, and 2205 stainless steel (control) were exposed to these environments and then subjected to direct pullout tests to evaluate bond strength. Thermal fatigue caused the greatest reduction in bond capacity for all bar types, with CFRP retaining better performance than AFRP.

The Jamestown-Verrazzano Bridge includes a 1509 meter long segmental concrete main structure that is supported in part by concrete-filled steel pile piles. The bridge was completed in 1992. In 2006 several small holes were observed in the pipe piles during an underwater condition inspection of the bridge. In 2011, during the next such inspection it was observed that the holes had not only increased in size but that there were additional holes. Based on a follow-on investigation it was determined that the source of the holes was microbiologically-influenced corrosion and that the onset of this condition appeared to be related to the breakdown of the piles’ protective coating. Having determined the source of the corrosion, a repair program has been developed and is underway.

An innovative floor anchorage system is under development for seismic-resistant buildings. The anchorage possesses a predefined “cut-off” load to limit inertial forces, transforming seismic demands into relative displacement of the floor system with respect to the primary vertical elements, and dissipating seismic energy in the building system. Elastic restoring, stabilizing, and re-centering elements complete the inertial force-limiting anchorage system (IFAS). The system has the potential to limit diaphragm forces, thereby lowering floor accelerations and reducing seismic demands on the lateral force resisting system, resulting in less damage to the structure, non-structural elements and building contents. The IFAS concept is being developed in a multi-university research project including meetings with design consultants for prototype development, computational simulation to optimize design parameters, full-scale component testing to determine prototype characteristics, and a half-scale shake table test to demonstrate the concept. This paper summarizes these efforts to date.

Recent research indicates that graphene and graphene oxide nanoplatelets can enhance the “smartness” as well as improve the strength of cementitious materials due to their unique mechanical, thermal, and electrical properties. Despite the great advantages and promising potentials shown in the graphene-reinforced concrete, its application to real construction demands a deep understanding of the graphene’s effects on concrete durability. To meet this need, this study is focused on studying the freeze/thaw performance and corrosion resistance of graphene-reinforced concrete. Different types of graphene and graphene oxide nanoplatelets, characterized by their size and oxidation, are used to cast mortar specimens for experimental investigation. The compressive strength, freeze/thaw performance, and corrosion resistance are recorded for each group and then compared with the benchmark samples containing no graphene nanoplatelets. To deepen the understanding of the graphene’s effects on concrete, nano-scale characterization is further carried out for each group. The microstructure of the cement paste around the graphene nanoplatelets, with a focus on morphology and Young’s modulus, is probed by using Atomic force microscopy (AFM). It is found that graphene nanoplatelets can significantly change the proportions of constituent phases in the cement paste, which can be directly correlated with the strength and corrosion resistance of graphene-reinforced concrete.

Although several self-centering seismic systems have been developed in the past, their implementation in practice has been relatively limited. Unusual field construction practices, perceived initial cost premiums and deformation incompatibility with the gravity framing are some of the issues that may be factors. A self centering beam moment frame (SCB-MF) has been developed that mitigates several of these issues. The self-centering beam (SCB) can be shop fabricated with a restoring force mechanism which eliminates deformation incompatibility and allows conventional field construction methods. The strength and stiffness of the beam are decoupled resulting in a cost-effective system that may be competitive with conventional moment frames. This paper describes an experimental program on two-thirds scale one-bay SCB specimens. Parameters that were varied in these tests include SCB depth, initial post-tensioning stress, ratio of initial post-tensioning force to fuse yield capacity, and nominal moment strength of the system. A detailed description of the test setup, post-tensioning procedure, and implementation of the energy dissipation fuse will be presented. Finally, the testing results including the behavior of the individual components (energy dissipation fuse, PT strands and beam) and global system behavior will be summarized.

This paper describes an experimental study and numerical modeling of unbonded post-tensioned (UPT) cast-in-place reinforced concrete (RC) walls subjected to quasi-static cyclic load. Design of the test walls is based on ACI 318-11 with the base moment capacity provided by the post-tensioned strands versus the moment capacity provided by conventional reinforcing bars as the main parameter. The experimental results showed that a UPT cast-in-place RC wall can sustain large deformations before failure. Two wall specimens were tested. The test wall with more post-tensioned strands displayed better response in terms of self-centering capability. One test wall failed in shear. One test wall failed by bar buckling and fracture. Numerical models utilized fiber beam-column elements and nonlinear truss elements. Results from numerical models and experiments are compared. Numerical results were consistent with the experimental results for maximum load capacity.

The Kettle River Bridge is an arched, steel cantilevered deck, Pratt Truss Bridge. In order to quantify the live-load performance of the bridge superstructure and provide a baseline for future comparisons, it was instrumented with 151 strain gauges on various beam, stringer and truss members. In addition, eight vertical displacement gauges were attached along the truss. All gauges were simultaneously monitored as the bridge was subjected to a non-destructive, live-load test. The recorded bridge response was analyzed to quantify in-situ behavior. The measured behavior was then used to validate a finite-element model using solid and frame elements, which was subsequently used to obtain an inventory and operating load rating of 2.03, and 2.64, respectively. Based on the results of the test, it was concluded that the large gusset plates added partial fixity to the truss members demonstrated by the significant measured in-plane bending strains. However, the beam-and-stringer deck support system behaved nearly simply supported between consecutive panels. The actual bridge distribution factors were found to be conservative, in comparison to those calculated according the AASHTO LRFD Specifications, by 17 to 44%.

Recent results from the large-scale experimental evaluation of a multi-story coupled shear wall system with fully post-tensioned coupling beams are discussed. In this novel system, high-strength unbonded post-tensioning (PT) strands are used to couple (i.e., link) reinforced concrete wall piers. To validate the new system, reversed-cyclic quasi-static testing of a 40%-scale coupled wall structure with the proposed details was conducted. The laboratory specimen represented the most critical bottom three stories of an eight-story prototype structure, consisting of two C-shaped wall piers, six coupling beams (two beams at each floor level), tributary slabs at each floor, and the foundation. The other (less critical) regions of the structure were simulated analytically. The test specimen performed well, demonstrating ductile behavior through the completion of three full cycles at a lateral drift greater than the 3.0% roof drift demand used in design, thus supporting the design approach, assumptions, approximations, and tools. Ultimately, the test results also support the ACI classification of these structures as “special” reinforced concrete shear walls in moderate and high seismic regions of the U.S.

A multi-hazard life-cycle methodology is used to assess the effects of flood-induced scour on the seismic system failure performance of bridge systems. Based on a case-study for a simple bridge system supported by shallow foundation systems, our results show that scour effects are time-varying: during the first 45 years, scour has insignificant effect on modifying the seismic vulnerability of the bridge in terms of two levels of system failures (i.e. extensive system damage or system collapse); after 65 years, scour dominates the cause to system failure; and while between 45 to 65 years, bridge scour and earthquakes jointly contribute to system failure. This result implies that caution is necessary for managing aging bridges serving in both seismicity and flooding active regions.

The Performance Based Seismic Design (PBSD) philosophy was introduced and first gained popularity in the United States about 20 years ago. Since then, seismic design guides, and some building codes, have increasingly adopted PBSD methodologies. Although the current nationally-recognized building code for new structures in the United States, the International Building Code, and its reference standards have incorporated certain facets of PBSD, seismic design of new structures in the United States is still based primarily on prescriptive rules rather than a performance-based philosophy. With each new edition of the American Concrete Institute building code, the ACI 318 Building Code Requirements for Structural Concrete, new and revised seismic provisions are introduced. To date, however, few of the recently-adopted changes in the ACI 318 code have directly supported implementation of the PBSD approach. The 2014 edition of ACI 318 has been completely revised into a format that is organized around the design and behavior of individual member types. This paper provides an overview of the current state of seismic design provisions in the ACI 318 code, and describes possible future ACI 318 developments that would further promote the implementation of PBSD for concrete structures.

Hurricanes are among the most costly natural hazards affecting communities worldwide. The landfall of a hurricane involves different hazard sources (i.e., wind, windborne debris, flood, and rain) that interact to generate the hazard scenario for a given structure. Thus, hurricanes can be viewed and must be analyzed as multi-hazard scenarios. In this study, a probabilistic Performance-Based Hurricane Engineering (PBHE) framework is used for the risk assessment of a residential structure subjected to hurricane hazard. A case study of a hypothetical residential house subjected to the combined hazards of wind, windborne debris, flood, and rainfall is considered to illustrate the sequential procedure for the probabilistic risk assessment. The results obtained from the application example include the annual probability of exceedance of total loss for the target residential building due to each hazard and their combined effect, and highlight the importance of considering the interaction between different hazard sources.

Multi-objective optimization for the probabilistic seismic performance based design of an example moment frame steel structure is presented. Direct economic and social losses associated with seismic events, which are of interest in the current recommended frameworks for the performance based design of structures, are considered in the optimization problem defined. Three optimization objectives are selected: the initial construction cost, modeled as the weight of the structural system; expected annual economic loss associated with damage resulting from seismic hazard; and expected annual social loss resulting from seismic hazard induced damage. Hazus recommended procedures are applied in the economic and social loss calculations which include the fragility functions used in the damage analyses and injury event models implemented in the social loss calculations. The multi-objective optimization method uses a non-dominated sorting genetic algorithm strategy. The optimization results for the multiple objectives are presented and discussed in the form of Pareto fronts. Engineering demand parameters implemented for the seismic loss analysis are inter-story drifts and peak floor accelerations and are obtained using inelastic time history analysis for the ground motions associated with various seismic hazard levels. To illustrate the design procedure, loss parameters are calculated for an example steel structure located in Los Angeles, CA.

The end corrosion in steel girders at the bearings due to joint leakage is a significant problem in many of the old bridges around the nation. This critical damage impairs the shear and bearing capacities of girders. This paper discusses a novel method for retrofitting the corroded ends of steel bridge girders using ultra-high performance concrete (UHPC) encasings. This repair method involves casting thin UHPC panels on each side of girder web. Shear studs welded to undamaged portion of the web and flange engage the UHPC panels and provide an alternate load path. This repair method is expected to be superior to the current practice of attaching steel cover plates. It can be easier to design and install, reduce obstruction to traffic during the repair, prevent future corrosion to the girder end, and reduce the total cost of repair. To investigate the effectiveness of the repair in recovering the capacity of the corrosion damaged girders, three large-scale experiments were performed on the undamaged, damaged and repaired rolled girders. It was found that a 1 3/4-in. thick UHPC panel cast two-third of the height of the girder effectively restores the bearing capacity. A high fidelity finite element model was created from the results of the large-scale experiments. This model was then used to design eight repair techniques for full size plate and rolled girders with heavy corrosion damage. This innovative repair method may offer the bridge design community a superior alternative retrofit method for large scale application on our aging bridges.

Various self-centering beam-column connections have been developed to mitigate the structural damage and post-earthquake residual drifts of seismic resisting moment frame building systems. However, their challenging on-site constructional complicity, and incompatible displacements with gravity bearing sub-structures and non-structural components may have hampered their potential of wide use in practice. Self-centering couple beams (SC-CBs) are a shop pre-fabricatable modular unit and do not require welding at the beam-column joints during on-site construction, allowing for conventional construction approaches but also simplifying field construction. Automatically retractable relative slide mechanism built within SC-CBs is a feature of the module. This feature reduces post-earthquake residual drifts of the applied structures and eliminates the displacement incompatibility of current self-centering beam-column connections with gravity bearing sub-structures. SC-CBs are developed with design parameters that can control peak story drifts of moment frame building systems, providing compatibility with displacement-sensitive non-structural components and mitigating displacement-included damage to non-structural components. This paper describes the SC-CB module concepts, conceptual construction procedure, design equations and considerations, connection details, and nonlinear modeling. A prototype SC-CB moment frame building was designed as an example. A nonlinear model for the prototype SC-CB structure was created using OpenSees. Static pushover analyses were conducted to verify proposed design equations and conceptual behavior. Dynamic time history analyses with 44 ground motion records scaled to the design basis earthquake level were performed to advance the knowledge of local and global behavior of SC-CB moment frame buildings under seismic loading. The peak and residual drifts from dynamic analyses were investigated to verify the displacement compatibility. Peak floor acceleration response from dynamic analyses was investigated for the effectiveness in reducing damage to acceleration-sensitive secondary structures or equipment of the prototype building. Structural steel weight of the prototype SC-CB moment frame was compared with a conventional moment frame with welded connections designed for the same prototype building. This comparison will service as an important factor when considering cost-effectiveness of using SC-CBs in building systems.

This paper reports on ongoing research involving the use of non-proprietary Ultra High Performance Concrete (UHPC) in closure pours (joints) between precast bridge deck elements. With the objective of exploring the lower limits of joint size, four specimens were designed based on existing information about the bond strength of steel rebars in UHPC and then tested to failure. The applied loading was such that the UHPC joints were subjected to either pure flexure or combined flexure and shear. Test results showed that all specimens suffered bond-related failures prior to steel yield. The reasons for the observed failures are discussed and related ongoing research is outlined.

Many coastal areas in the U.S. are subject to tsunami hazard. The public safety risk has been partially mitigated through warning and preparedness of evacuation, but community disaster resilience requires that critical and essential facilities provide structural resistance to collapse. Furthermore, there are coastal communities in the states of Alaska, Washington, Oregon, California, and Hawaii where there is insufficient time for evacuation. The Tsunami Loads and Effects Subcommittee of the ASCE/SEI 7 Standards Committee has developed a new Chapter 6 - Tsunami Loads and Effects for the 2016 edition of the ASCE 7 Standard, Minimum Design Loads for Buildings and Other Structures. The ASCE 7-16 Tsunami Loads and Effects chapter will become the first national, consensus-based standard for tsunami resilience for use in the states of Alaska, Washington, Oregon, California, and Hawaii. The new ASCE 7 provisions implements a unified set of analysis and design methodologies that are consistent with probabilistic hazard analysis, tsunami physics, and structural target reliability analysis. The approach developed by the ASCE Tsunami Loads and Effects Subcommittee results in the first unification of tsunami hazard mapping for design and would reflect a modern approach of Performance-Based Engineering, in which explicit reliability targets for performance are used in the development of the design requirements. The purpose of this paper is to provide an overview of the technical basis and methodology for tsunami-resilient design of critical and essential facilities, taller building structures, and tsunami evacuation refuge structures.

This study aims to provide a comprehensive method for modeling and analyzing prestressed concrete substructure elements, specifically wharf piles, subjected to chloride-induced corrosion. Fully understanding this process is crucial to capturing uncertainties in structural response and providing accurate predictions of its time-dependent degradation mechanisms. A probabilistic modeling framework and detailed finite element model and analysis are employed to explore these effects. Results indicate a high degree of uncertainty captured by the spatial and time-dependent modeling techniques in addition to stress corrosion cracking and brittle failures modes observed in the finite element analysis.

It has been recognized that the quantitative performance evaluation of corroded reinforced concrete (RC) structures could aid in developing effective repair strategies. However, the current performance evaluation only focuses on the ultimate strengths criteria and do not consider the serviceability requirements. To consider both criteria and to facilitate the analysis, an analytical procedure is proposed for predicting the load-deflection behavior of intact and corroded RC beams. The corrosion effects considered here include the effects of corrosion on the area and yielding strength of the rebars, and the bond stress-slip behavior at the steel-concrete interface. The proposed procedure is then utilized to evaluate the time-dependent reliability of an RC beam with and without repair in terms of flexural strength and deflection performances. The effects of relative humidity and mixture design are also studied.

Performance-based design (PBD) is becoming the benchmark approach for designing civil structures that rationally meet society’s need for a truly safe built environment. While the principles of PBD have been widely adopted in the field of seismic engineering, the same cannot be said for wind engineering. This paper represents a first attempt to define an appropriate framework to allow the principles of PBD to be fully embraced during the design of building systems to resist severe wind events. Focus is placed on highlighting the necessary steps to reach such a goal, which include the definition of site-specific wind hazard models, of suitable fragility functions as well as of consequence functions that rationally assess damage and losses, while communicating performance in ways that are meaningful to decision-makers. The application of the framework to a case study provides the basis for a discussion on the future challenges that researchers in performance-based wind engineering will have to embrace.

Bridges serve as critical links in a transportation network. Closure of bridges due to damage resulting from an extreme event, such as an earthquake, can disrupt the transportation operations on the network leading to, potentially significant, economic and social losses. Rapid and simultaneous restoration of all damaged bridges is an ideal solution for minimizing these losses. However, this solution is not realistic for extreme events that might damage hundreds of bridges when considering limitations on the available financial and physical resources. Optimal restoration solutions, i.e. restoration designs, for disrupted transportation networks have been studied in the past. Most of these studies have relied on maximizing or minimizing one or two technical objectives, such as network functionality and restoration costs. However the restoration of a disrupted transportation network is necessarily complex due to the various economic and social aspects that need be considered, for example lost opportunity and mobility of citizens. A framework based on a many-objective approach, i.e. more than three objectives, that considers a broader array of technical, social and economic aspects so that robust solutions for the restoration design of damaged bridges on a distributed network can be identified is presented in this paper. The many-objective framework is applied to an example network to obtain robust solutions and compare these solutions to those obtained from optimization considering one and two technical objectives.

Agent-based modeling (ABM) is a powerful tool for model complex and heterogeneous systems as pedestrian evacuation after extreme events. Several studies on Emergency Management exist in literature, but the majority of them do not consider how human behavior impacts the evacuation plan. Indeed, these can change drastically a critical scenario because are driven by emotions, knowledge and perception which are unpredictable. The aim of this study is to develop an ABM of an evacuation scenario due to a blast in a public area integrated with a mathematical dynamic human behavior model. Netlogo, which is a multi-agent programmable environment, was used to build the ABM. ABMs simulate two phases: the normal phase and the agent’s evacuation process after the blast. The evacuation time is the main parameter of response and it is used to evaluate the efficiency and safety of an infrastructure. Each agent has its own behavior according to a layered framework mathematical model. The first layer, thanks to an empirical statistical distribution, simulates the “agent’s state” function of the role performed by the agent and his age. Then the” individual module” describes the emotional aspects using the Decision Field Theory. This ABM becomes an important tool that enables designers or policy makers to test, estimating and improving the response of infrastructures in hazardous scenario.

Buildings and infrastructure systems support housing, business, government, industry, and other vital services in communities. The concept of disaster resilience addresses the way that communities prepare for and recover from disruptive events. Needs of citizens and institutions in a community define the performance requirements for buildings and infrastructure systems, including the recovery in the aftermath of damaging hazard events. However, current practice does not adequately address risks and reliability at a community systems level, interdependencies between systems, or the role each system plays in recovery. NIST has established a research program to improve guidance, standards, and tools that support community disaster resilience planning. The immediate research has been initiated with guidance documents to identify best practices and research needs. The longer term research includes development of metrics and tools for communities based on integrated systems modeling at a community level.

Once finished in early 2016, the Ocosta replacement elementary school in Westport, WA will be the first tsunami vertical evacuation structure in the country. Tsunami-resistant design for the building was performed using provisions which will be published in ASCE 7-16. A benchmarked site-specific inundation model was used for hazard characterization. The school structure was designed to resist hydrostatic, hydrodynamic, scour, and impact forces through various strategies. Pile foundations were designed to resist potential liquefaction at the site and provide residual gravity and lateral resistance with the upper 3.7 m of soil assumed to be scoured. Concrete shear walls were designed to resist seismic and inundation-related lateral forces and offer toughness and ductility to resist impact loads. Structural steel gravity columns were designed to resist expected impact loads and moment-resisting beam-column connections at the refuge level provide alternate-path progressive collapse resistance for unexpected impact forces.

Emergency management and building loss assessment are the next steps after the first emergency response to recover from extreme events like an earthquake that threatens life, property, operations, or the environment. Emergency responders now have access to many different social media tools such as smart phones, high-speed internet, and “cloud” computing, to name only a few examples that have the potential to improve the way they do their jobs, allowing for near-instantaneous exchanges of information. Social media can help people in different communities and locations collaborate in new ways. While social media tools offer the potential for improving emergency management, public organizations such as emergency authorities may not fully understand how these tools can help them. Since the use of smart phones is becoming more and more spread among the population, its utilization within the field reconnaissance has been proposed in this paper. The application can be run by residents on smart phones and has been recently and tested during 2014 Napa Valley Earthquake in California. The application gives an initial damage evaluation of the area, which is going to be very useful when the number of inspectors is limited. The application is freely available both in the Apple store for iOS users and in the Google store for the Android users. Potential uses, recommendations, and limitations are also presented.

As design professionals we are used to tackling problems involving the environment, transportation and civil infrastructure, buildings, bridges, and their subsequent construction projects, etc. In doing so we often abide by a credo such as South Carolina Regulation 49-301 which states: “The Engineer or Surveyor shall hold paramount the safety, health, and welfare of the public in performance of his professional duties”. However, what we as a collective group may not be ready to tackle is the response to manmade or natural emergencies or disasters. Have you ever asked “How can I help to restore and maintain the safety, health and welfare of the public following such an event”? The purpose of this paper will be to illustrate the ongoing process of developing emergency and disaster preparedness procedures in South Carolina through organization collaboration and community outreach. The overall disaster preparedness and response model in the State of South Carolina will be presented and the roles that volunteer engineers and community members play will be discussed. Specific issues covered will include: collaboration between engineering organizations with the local and state authorities through preparedness exercises, the development of awareness guides, as well as education and training of design professionals through the Safety Assessment Program (SAP) and civilians through the Community Emergency Response Team (CERT) initiative.

A comprehensive resilience management program goes beyond good structural engineering design. It includes: Risk Avoidance, Risk Transfer and Risk Adaptation. This paper describes three practical cases studies which employed a range of engineering based strategies to improve resilience of a building owner's physical assets using all three methods. These include: two state court facilities where the structural engineer employed Performance Based Engineering to determine the life cycle return on investment of multiple structural design options; a California healthcare provider that used Quantitative Risk Engineering to quantify the property and business interruption risks and optimize its earthquake insurance program; and a university that has established a robust emergency response and recovery program that includes training of hundreds of staff on basic building damage assessment, to speed recovery following a major seismic event.

The paper presents a simplified model that describes the ability of the Hospital Emergency Department to provide service to all patients after a natural disaster or other emergency. The waiting time is the main response parameter used to measure hospital disaster resilience. Several steps are taken to build a valid analytical framework. First, a generic simulation model of the emergency plan was developed taking into account the hospital resources, emergency rooms, circulation patterns and patient codes. 100 simulations were carried out using as input data the seismic arrival cycle. The results show that the waiting time for yellow codes, when the emergency plan is applied, are reduced by 96%, while for green codes by 75%. The peak waiting time for the yellow codes is about 30 min, for green codes is about 3.5 hours. Then, using the results obtained from the simulations, a metamodel has been developed .It provides the waiting times of patients as function of the seismic input and the number of the available emergency rooms. Finally, the metamodel has been generalized, releasing it from the particular characteristics of the analyzed hospital.

Spray-applied fire-resistive materials (SFRM) is one of the most widely used passive fire protection material for steel structures in North America. However, SFRM is inherently brittle and tends to dislodge or delaminate under extreme loading conditions (earthquakes or impacts) and even normal service load. Such loss of fire protection material puts the steel structure in great danger in subsequent fires. To address this concern, a new type of ductile spray-applied fire-resistive material, namely spray-applied fire-resistive engineered cementitious composite (SFR-ECC), has been developed recently as a durable alternative to conventional SFRM. SFR-ECC exhibits a ductile strain-hardening behavior with tensile strength, tensile ductility and interfacial adhesion (to steel) of 1-2 orders of magnitude higher than those of conventional SFRM under static loads. In the present paper, the behavior of SFR-ECC under high rate loading was experimentally studied. SFR-ECC maintains desired tensile performance under high rate loading, ensuring the performance of such material under impact or earthquake loads. Low velocity impact tests were also conducted on SFR-ECC protected steel beam and panel. SFR-ECC protected steel system showed much higher impact resistance than conventional SFRM protected ones. The integrity and functionality of SFR-ECC were well preserved after multiple impacts while conventional SFRM experienced catastrophic failure. This experimental study further demonstrated the advantages of SFR-ECC over conventional SFRM under severe loading conditions, which is critical for the fire safety of steel structures under multi-hazards.

In recent years, severe hurricanes have caused enormous economic losses for the society and placed a tremendous burden on the insurance industry. Although different retrofit measures can be used to mitigate hurricane damage and reduce the associated social and economic losses, it is a challenge to choose the most cost effective one. In the case of residential buildings, the resources available for hurricane risk mitigation are limited and the upfront costs of improved design alternatives and retrofit measures are usually high. In this study, a probabilistic Performance-Based Hurricane Engineering (PBHE) framework is used to compare the effectiveness of different hurricane retrofit techniques for residential building from a cost-benefit point of view. A realistic case study is presented to illustrate the methodology and to evaluate the costs and benefits of different hurricane hazard mitigation techniques and design alternatives for residential buildings over the entire design life of the benchmark building.

The objective of this paper is to outline a Performance-Based Engineering (PBE) framework to address the multiple hazards of earthquake and Fire Following Earthquake (FFE). Fire codes in the United States are largely empirical and prescriptive in nature. The reliance on prescriptive requirements makes quantifying sustained damage due to fire difficult. The very nature of fire behavior (ignition, growth, suppression, and spread) is fundamentally difficult to quantify due to the inherent randomness present in each stage of fire development. The study of interactions between earthquake and fire is in its infancy with essentially no available empirical testing results. A generalized PBE framework for earthquake and subsequent FFE is presented along with a comparative hazard probability to performance objective matrix and a table of variables necessary to fully implement the proposed framework. Future research requirements, summary, and discussion throughout are provided to describe the cascaded hazards of earthquake and FFE.

The concept of resilience has moved the structural engineering community from thinking of the survival of individual buildings to the role of buildings in the community. Performance-based design of buildings includes consideration of the damage levels associated with various hazards, as well as the impact of building damage on community performance, both in the immediate aftermath of a disaster, and during the recovery phase. This paper examines various definitions of resilience, and how some of them can be quantified. It discusses the relationship of individual buildings and the community portfolio, and the importance of community aspects that are not normally considered by engineers, such as social vulnerability and economic impact. The paper includes a discussion of multifaceted losses such as business characteristics.

The engineering community has recently started to implement methodologies that incorporate explicit risk assessment principles and performance-based criteria to design new structures efficiently, assess the safety of existing structures, and manage our deteriorating civil infrastructure systems. Particular attention has been paid by structural engineers to extending the design and safety evaluation processes from their original focus on the components of a single structure, such as a building or a bridge, to a more complex approach that considers the performance of an entire structural system and, on an even larger scale, a network of structures. The interest in risk analysis techniques has been strengthened by recent extraordinarily destructive events, including Hurricanes Sandy and Katrina, Fukushima Earthquake in Japan and other disasters that have devastated the affected communities. A survey of attitudes of structural engineers and their agencies to risk-informed structural engineering practices and a follow-up workshop have recently been completed. Both the survey and the workshop were conducted under the auspices and financial support of the Structural Engineering Institute (SEI) of ASCE. The paper summarizes the feedback received from the experts who responded to the survey or attended the workshop. It compares the progress made in different sectors of the structural engineering field, addresses some of the significant impediments, and points the way forward.

Day-to-day environmental and operational conditions that lead to deterioration of in-service structures are most often addressed through prescriptive inspection routines or handled on an ad-hoc basis. These approaches lack effectiveness if inspections are untimely or efforts are misdirected. Gains may be realized by following risk-based inspection paradigms in civil infrastructure. Related industries, such as the oil and gas, chemical process, energy and commercial aerospace sectors have long been applying risk-based methods to perform hazard assessments and to then prioritize the inspection and maintenance of structures and systems. These risk-based methods are used to identify, evaluate and control hazards, many of which involve more typical day-to-day deterioration hazards in addition to rare, high-consequence hazards. This paper will serve to highlight hazard assessment techniques and risk-based inspection methods from related industries and suggest how analogous methods may be used for civil infrastructure.

A probabilistic approach to lifetime assessment of seismic resilience of concrete structures under corrosion is presented. The seismic capacity is assumed as time-variant functionality indicator and the seismic resilience is evaluated based on a suitable analytical representation of the functionality recovery profile. The proposed approach is applied to a four-span continuous bridge with box cross-section piers exposed to corrosion. A parametric analysis is performed to highlight the influence of the main factors of the recovery process. The results show that the detrimental effects of structural deterioration may affect the effectiveness of the recovery process and lead over time to a significant increase of uncertainty of the seismic resilience.

Performance based design with seismic protection devices such as viscous dampers have fundamentally altered the landscape of earthquake engineering and design. Structures designed and built without such devices typically use a code-prescribed design that implies extensive structural damage, loss of operation, and likely replacement at design-level earthquake. In contrast, performance based design incorporating earthquake protection devices leads to a combination of best engineering practice and reducing life-cycle costs. These devices are robust, cost-effective, and have a proven exceptional performance record in past earthquakes. In most cases, initial cost of their utilization is neutralized by reduction in cost of other structural members. The long-term performance is the key parameter used for evaluation. Structures properly designed with these devices will likely only require minimum post-earthquake inspection and can be fully operational within hours of a seismic event. When utilized for critical structures, such performance reduces the need for use of natural resources by eliminating post earthquake repair or reconstruction and thus improving the community resiliency. Example cases are presented

There are several evolving design procedures aiming to mitigate disproportionate collapse of buildings to malevolent threats. The Specific Local Resistance (SLR) concept is often the least used in practice. Testing and computational research indicate that hesitations in deploying SLR designs are not necessarily warranted and column’s directly exposed to malevolent blast threats can be enhanced by smartly designing around their potential failure modes. The objective of this paper is to introduce SLR in the context of mitigating disproportionate collapse of buildings. This is done through computational case studies on disproportionate collapse and exploring the SLR of reinforced concrete and steel columns through test data and computations.

Steel/Aluminum grid shells—a key structural concept selected by notable Architects such as HOK, Fosters, AECOM, and others for institutional & commercial projects resulted in the design/construction of innovative skylights, walkways & bridges. Built facilities offered clear view of the sky that makes it feel like outdoor spaces with controlled temperatures.

Retractable roofs around the world have been designed to allow light and a sense of openness for the spectators but they are either fully open or fully closed. A roof that adapts to the environment and to the functional needs of the venue as it relates to environmental conditions in addition to providing added functionality for the stadium has the potential to transform the way roofs are designed and operated. This paper explores the historical precedents of retractable roof structures and their current functionality, the need for a more adaptive solution, current kinetic structure concepts, and a presentation of innovative solutions.

Steel-framed gypsum partition walls are comprised of light-gauge cold-formed steel studs and tracks, gypsum boards and the screw connections between them. The tracks are also fastened to the structural slab with power-actuated fasteners. Previous experimental studies have shown that the seismic performance of partition walls depends on the force and displacement characteristics of these components. A series of component-level experiments were performed, aiming to investigate both monotonic and cyclic behavior of partition wall components, including gypsum-to-stud, stud-to-track, and track-to-slab connections. The experimental data was then utilized to propose and validate a series of nonlinear hinge models for these components in the OpenSees. Subsequently, the hinge models were used in conjunction with the analytical models of gypsum boards and steel studs to develop a comprehensive analytical model for a typical partition wall assembly. The model was calibrated using the available data from a full-scale test on the steel-framed gypsum partition walls.

In the 1970s, seismic analysis was performed for a Pumphouse type structure using FLUSH computer program, which is capable of producing a time domain solution to the Soil-Structure Interaction problem. The structure was modeled using two 2-D planar models is each horizontal direction. The density and modulus of elasticity of each element was adjusted to represent the response characteristics of a 2-D lumped mass representation of the structure. The soil profile characteristic of the site consists of relatively stiff soil. A wedge next to the structure was partially backfilled with a clayey fill type material. Recently, a plan was made to excavate the clayey fill and to backfill with a stiffer gravelly mixed soil. In this paper, a model is generated using SASSI computer code with the Random Vibration Theory solution approach, to match the 1970s era analysis. Once, the results are compared and deemed to correlate, the changes to the backfill condition are considered in a second SASSI analysis. The seismic responses of the two backfill configurations are compared.

A failure analysis was conducted following the collapse of a 13,000 lbs., 165 ft by 16 ft rectangular steel suspended ceiling panel structure in a large public space. The ceiling framing structure was suspended from the roof structure with a unique system of stainless steel cables that cross one another between the ceiling structure attachment points and the anchorage to the supporting slab above. During construction, the entire ceiling panel structure rotated out of its installed horizontal position when the temporary cable bracing was removed, causing one edge of the ceiling structure to drop suddenly and the opposite edge to lift. No failure of the suspension cables or their attachments occurred. The collapse was caused by a design error that did not properly consider the stability of the suspended ceiling panel. The behavior of this particular ceiling panel structure is generalized to a wider class of crossed pendulum structures, and stability conditions based purely on system geometry are found using energy principles for a wide set of feasible parameters. Guidance is provided for the design of suspended systems involving crossed hangers, such as ceiling structures, bridges, and suspended walkways.

Design of offshore wind farm substructures and foundations require several considerations. Constant soil-structure and structure-environment (wave and wind) interaction calls for comprehensive understanding of structural behavior under complex loading patterns. Due to the dynamics of the Wind Turbine Generator (WTG), dynamic response of the substructure and foundation should fall in pre-defined, narrow band response spectrum. Procurement and fabrication of these structures is another limiting constraint to consider in the design process. Availability and limitations of manufacturers and simplicity of construction are critical parameters in the successful design process. Most of the structural components need to be transported to the installation site in the sea and then installed with specialized marine vessels. Both the transportation and installation of offshore wind farm substructures and foundations utilize expensive marine equipment and the offshore processes are weather limited. Keystone Engineering’s Inward Battered Guided Structure (IBGS) provides an optimum solution to the challenges of design, manufacturing, transportation and installation in a range of shelf water depths. Flexible design configurations provide freedom for the designer to add or remove elements without loss of structural integrity, to allow adjustment adjust for resonance response avoidance. Efficiency is achieved in manufacturing by reducing the number of members and weldments and thus, minimizing the lifts of subassemblies. Ease of transportation with marine vessels is improved by reducing the footprint space requirements and the choreographed installation procedure can lower the vessel charter costs significantly. These design considerations make IBGS an efficient choice for substructure and foundation of offshore wind farms.

Manufacturers of utility-scale wind turbine generator systems (WTGS) face fierce global competition from producers of other forms of energy-generating equipment as well as other WTGS manufacturers. Accordingly, many manufacturers focus on innovation to continually reduce the overall cost of energy while ensuring safe and dependable long-term power production. Presenting a lower overall cost of energy results in the increased attractiveness of wind energy to potential developers and provides competitive advantage opportunities to manufacturers within the wind industry itself. Considering that there are generally no direct fuel costs associated with WTGS energy production, initial capital expenditures for the system and associated Balance of Plant items constitute most of the overall cost of energy. Wind tower support structures themselves represent a sizeable portion of the WTGS cost. This paper addresses tubular steel wind turbine tower design optimization approaches employed in engineering practice to reduce tower costs. Examples of advanced optimization topics include:

This paper’s target audience includes stakeholders in the utility-scale wind energy industry such as: (1) structural engineering professionals, (2) siting engineers, (3) project developers, (4) and project and construction managers in the wind power plant planning phases; and (5) others with interest in design aspects of the green/renewable sector of the engineering market. This paper has the following learning outcomes: (1) to provide an overview of advanced topics not otherwise apparent to those outside of the wind industry; (2) to illustrate some of the many idiosyncrasies of wind industry practice for tubular steel tower design.

Damage to nonstructural systems during an earthquake can leave a building inoperable, causing economic losses, and extensive downtime. Among these nonstructural systems, partition wall damage has been reported frequently during past earthquakes while the seismic response of these systems is poorly understood. To better understand the seismic performance of integrated ceiling-piping-partition systems, a series of full-scale system-level experiments using a two-story steel bracedframe structure was conducted at the University of Nevada, Reno Network for Earthquake Engineering Simulation site. In this study, responses and behaviors of partition walls were critically assessed through several design variables including: 1) framing systems, 2) partition wall heights, 3) partition wall geometries, 4) openings in partition walls, and 5) top connections. Experimental fragility curves were developed based on damage caused from inter-story drift. Along with fragilities, out-of-plane acceleration amplification factors for partition walls were computed. This study showed that the acceleration amplification factors for out-of-plane partition walls are comparable with the recommended amplification suggested by the code for flexible components.

This paper summarizes the experimental studies to assess the seismic performance of a commercially available vibration isolation platform. The studies consisted of earthquake simulation tests using a three-directional earthquake-simulator. The test specimen included a vibration isolation platform, based on negative stiffness springs, supporting generic/simulated equipment. The platform-equipment set was subjected to seismic shaking that intended to simulate a variety of ground and floor accelerations of multistory buildings under low-intensity earthquake shaking. This paper includes: (1) a description of the isolation platform and experimental settings, (2) sample of experimental results, and (3) findings on numerical analysis of the isolation platform placed in different floors on a multistory-story building subjected to ground shaking that may be representative of moderate/low seismicity areas. The paper concludes on the performance of the vibration isolation platform for seismic protection of equipment in different buildings floors.

Opportunities to investigate numerous floor tile and wall tile installations after they have sustained functionality failures, mainly in south Florida, indicate that there is a level of resistance, a lack of understanding, and/or a lack of awareness of appropriate knowledge imbued by some of the industry professionals, designers, contractors and/or trades performing the tile installations. Observed failure conditions indicate substantial neglect with respect to requirements documented in the building codes, the ANSI (American National Standards Institute) standards, and/or manufacturer installation instructions. Such literature comprises the tile installation “industry standards”. Case studies will be described and discussed that include various tile materials such as stone, porcelain and ceramic utilized in various flooring and bathroom wall tile installations that have experienced a failure. The repeated non-compliance with the appropriate industry standards during the installation process demonstrates a level of neglect that has resulted in failure due to inappropriate construction practices. This indicates that it has become common for installers to cut corners, as observed by the poor installation techniques and workmanship in the case studies presented herein. Building code requirements, industry standards and manufacturer instructions often utilized by south Florida industry professionals include: the Florida Building Code; Horizontal Surfaces – an Excerpt from the Dimension Stone Design Manual, 7.1 by the Marble Institute of America; the Tile Council of North America (TCNA) Handbook for Ceramic, Glass, and Stone Tile Installation (2011); and the ANSI A108.01, A108.1A, B and C, A108.02, and A108.5, American National Standards for the Installation of Ceramic Tile. Additional relevant information also includes select manufacturer instructions and guidelines for various associated materials and components. The historical Southern Standard Building Code and the subsequent South Florida Building Code were the precursor codes and partial basis for the current Florida Building Code. In research of building codes extending as far back as the 1985 Standard Building Code, tile installation requirements included explicit reference to the ANSI A108 standards as well, and these requirements still exist today in the current Florida Building Code editions.

This paper describes the fault crossing design of a new 66-inch buried pipeline. The new pipeline together with three older (69-, 90-, and 96-inch diameter) pipelines called Alameda Siphons connect the Coast Range Tunnel (CRT) on the east to the Irvington Tunnel on the west of the approximately 0.5-mile wide Sunol Valley. Near the eastern end of the valley, the pipelines cross the Calaveras Fault. The new pipeline was designed to remain in continuous operation when subjected to approximately 4-feet of fault displacement to meet the reliability goal of 120 million gallons/day within 24 hours of the earthquake. The design considered uncertainty in fault location, rupture displacement, and subsurface conditions. Design considerations also included pipeline alignment across the fault, pipe thickness, exterior coating and interior lining, trench design and backfill properties. An important aspect of the design was the tie-in to the existing 1933 era CRT portal located approximately 500 feet from the fault crossing location.

A simplified analysis procedure named Fault Rupture-Response Spectrum Analysis (FR-RSA) method was recently developed as an alternative to the rigorous but onerous nonlinear Response History Analysis (RHA) method for bridges crossing earthquake fault rupture zones. To validate the FR-RSA method, this research investigats seismic response of a representative four-span curved bridge in California. The selected bridge was analyzed using both the FR-RSA method and the nonlinear RHA method for comparison purpose. Ground motions, earthquake fault rupture locations, and fault orientations were varied in the analyses to expand the validation work under a broad range of the parameters. Result comparisons show that the FR-RSA method provides estimates of peak bridge displacement response that are close enough to the “exact” nonlinear RHA results in all considered cases; therefore, it is recommended for future practical application.

The default procedure indicated by the current seismic design code in the United States (ASCE 7-10) to determine seismic demands on acceleration-sensitive nonstructural components (NSCs) is a practical but perhaps somewhat overly simplified procedure that is intended to be applicable to NSCs located in any type of structure, regardless of whether the structure behaves elastically or inelastically, regardless of the fundamental period of the structure, and, perhaps more importantly, regardless of the kind of structural system. This paper investigates the differences between floor accelerations in Special Steel Moment Frames (SMFs) and in Buckling Restrained Braced Frames (BRBFs). The building structures analyzed in this study were taken from the ATC 76-1 project, and their mathematical models are very detailed since they were also used to evaluate collapse performance using the FEMA P-695 methodology. Floor accelerations were obtained through linear and nonlinear time history analysis, and results are expressed in terms of Peak Floor Accelerations (PFAs, which is the acceleration demand on “rigid” NSCs) and Floor Response Spectra (FRA, which is the acceleration demand on “flexible” NSCs). It is found that floor accelerations generally exhibit similar trends in both structural systems (SMFs and BRBFs), but the differences are large enough to justify further research on the development of practical procedures where the type of structural system is taken into account.

Subcommittees of the American Society of Mechanical Engineers (ASME) and the International Window Cleaning Association (IWCA)—namely ASME A120, which writes and maintains the standard ASME A120.1 Safety Requirements for Powered Platforms and Traveling Ladders and Gantries for Building Maintenance, and IWCA I-14.1, which writes and maintains the standard IWCA I-14.1 Window Cleaning Safety—have in recent years adopted a concept of “half-load” testing. Half-load testing refers to the limits imposed by these voluntary standards on load testing of existing facade access structural support equipment for the purpose of verifying required capacity. In each case, the voluntary standard prohibits testing beyond 50 percent of the minimum OSHA required strength. This paper highlights the folly of the half-load testing concept adopted and promulgated by A120 and I-14.1, and is intended to educate engineers involved in the certification of facade access equipment about the dangers of such an approach. A number of case studies are provided that demonstrate how half-load testing can fail to identify critical problems in structural elements.

In projects with geometrical complexity, the facade engineer is presented an opportunity to understand and influence the application of parametric tools towards logical geometry by rationalizing complexity. This requires a familiarity of the parametric tools often controlled by the design architect. This paper explores the injection of the façade engineer into a parametric workflow, describing their involvement from estimating through completion of the built structure. This is a project review of the structural engineering and construction process undertaken by a specialty facade contractor responsible for the installation of the Fulton Street Transit Center’s Sky Reflector-Net in New York City. The construction included an interior atrium shaped by a double-curved tensioned cable net clad by a perforated metal panel system. Light penetrates the atrium through an oculus before being redirected into the depths of the Center, providing the subterranean levels with a connection to daylight. A two-way cable net of paired cables was preassembled off-site, delivered on a spool, raised in a single lift and then tensioned. Attached to the cable net are 952 unique metal panels cladding the 8524 sf surface. A parametric workflow was implemented for collaboration between estimating, design and structural engineering using a common database of geometry information. This process was initially implemented to automate the generation of each metal panel’s unique geometry. The structural analysis tool Space Gass was used to perform the structural analysis, but utilized the geometry and naming conventions common to the database so that the results seamlessly integrated back into the workflow. This first analysis validated the component sizes and details for structural adequacy. Secondly, for fabrication purposes, one of the most significant contributions from the structural model was reverse engineering to determine the initial unstressed cable net geometry. This iterative analysis was used to predict (within an acceptable tolerance) each individual cable segment’s elongation to determine the initial length of each cable. Additionally, the location of each cable intersection node was determined to ensure the final form would be within construction tolerances. The role of the structural engineer in the façade contractor’s collaborative parametric workflow proved paramount in establishing the fabrication, assembly and installation means and methods for the project.

Taller, more economical wind turbine support towers are necessary for the future optimization of wind energy generation. Trends in current wind tower designs clearly demonstrate this need. Many large turbine manufacturers have begun production on large towers (taller than 120 m) that employee non-traditional wind turbine tower manufacturing techniques. Keystone Tower System’s (KTS) spiral welding manufacturing process for tapered steel towers is one example of a potential tall-tower manufacturing solution. Spiral welding is common in the pipeline industry where structural demands are influenced by internal pressurization. In contrast, the demand on wind turbine towers is dominated by flexural loading without internal pressurization. The lack of existing studies on the flexural behavior of spirally welded tubes is exacerbated by the high sensitivity to local buckling inherent in wind turbine towers, which have diameter-to-thickness ratios (D/t) that can exceed 300. For such structures, failure is dependent on initial geometric imperfections, including those induced by welding and other manufacturing procedures. Since spirally welded wind turbine towers will have a unique combination of welds, the impact of this particular manufacturing process on the ultimate local buckling strength of the towers must be understood. For this reason, a series of static, flexural tests have been undertaken on large scale spirally welded tubes. The preliminary results of these tests will be presented and discussed.

The interest on renewable energy has significantly increased the use of photovoltaic (PV) panels on low-rise buildings. According to the US Department of Energy SunShot Initiative studies, balance of system (BOS) costs account for about half of the total PV system cost and need to be reduced by 72–80% in order to achieve the program goals. One of the factors that has a direct impact on initial BOS cost (as well as on failure risk and market growth) is the lack of efficient wind design and adequate manufacturing guidelines for rooftop PV systems. The majority of wind related studies has been conducted on models of flat roof commercial buildings. The size of such structures as well as that of typical atmospheric boundary layer wind tunnels allowed only for small-scale tests. The current study is trying to address the above two issues; i.e., lack of large-scale wind tunnel tests and PV panel configurations specific to low-rise residential buildings. In order to study the wind-induced loads on PV panels, large-scale (1:6) models of residential buildings with roof-mounted PV panels were tested in the Wall of Wind (WOW) facility at Florida International University. Three types of roofs were considered; i.e., flat, gable, and hip roofs. The effect of a number of factors was evaluated, such as building height, roof to panel clearance, panel tilt angle, and area averaging effects. The PV panels were instrumented with pressure taps on both top and bottom surface so as to estimate the total net wind-induced forces. The tests were conducted for several wind angles of attack and the findings present the critical load cases for the configurations that were tested. Moreover, the area-averaging effect is discussed in detail and the results are specifically formatted for codification purposes (ASCE 7).

Suspended ceiling and fire sprinkler piping systems are one of the most vulnerable types of nonstructural systems that suffered costly damage during past earthquakes. The seismic performance of these two systems is poorly understood due to their heterogeneous nature. In order to fill this technical gap, a numerical modeling methodology is proposed for the integrated ceiling and sprinkler (CP) systems using the OpenSees software. This numerical simulation incorporates several experimentally calibrated component models for the pipe and ceiling joints as well as the supporting elements (e.g. braces, hangers) of CP systems. The propagation of seismic damage in CP systems and falling of ceiling panels are accounted for by using an element removal algorithm. The modeling technique is then validated using the experimental results of a CP system installed in a full-scale five-story building. The modeling method proved to be successful in predicting the pattern and location of failure in these systems.

Successful development of the offshore wind energy resource depends upon the reliability of the structures that support the electricity-generating rotor-nacelle assemblies that form the core of a wind turbine system. The risk posed to offshore wind turbines (OWTs) by extreme environmental events such as Atlantic hurricanes requires a more detailed examination of post-elastic structural performance during events occurring at greater return periods than the design conditions. This paper focuses on the assessment of the fragility of OWTs with jacket-type support structures under extreme environmental loadings. Performance levels ranging from undamaged to near collapse of the jacket supported OWT are defined and are assessed using static pushover analysis of the support structure for given wind and wave conditions. A numerical example is presented based on an environmental hazard model for a site off the coast of the state of Massachusetts along the Atlantic coast of the U.S. Using probabilistic models for the structural demands and capacities, fragility curves are developed for two damage states. It is shown how such fragility curves can be convolved with estimates of the economic consequences associated with the various performance levels to develop a complete risk profile for the support structure.

Seismic vulnerability of buried pipelines has been identified in many post-earthquake reconnaissance reports. Efficient retrofit of critical lifelines to improve their seismic performance becomes an urgent requirement nowadays. The cured in place pipe (CIPP) liner technology is an effective trenchless method for repairing existing underground lifelines with minimal ground surface disruption. However, the seismic performance of CIPP liner-reinforced pipelines is lacking verification and quantification. This paper presents and discusses the results of full-scale quasi-static and seismic tests conducted on water-pressurized ductile iron (DI) pipelines reinforced with one type of CIPP. The axial behavior of the liner-strengthened DI pipelines under static cyclic loading and their seismic response under transient ground deformations (TGD) during earthquakes has been investigated in this paper. Moreover, numerical models have been developed to simulate the axial behavior of liner-reinforced joints under cyclic loading. The results indicate that CIPP liner substantially increases the longitudinal stiffness and strength of the joints of segmental DI pipelines and significantly improves their seismic behavior under high intensity TGD.

Significant damage and collapse of suspended ceilings have been observed in past earthquakes. To address such vulnerability, design and installation requirements have been introduced in the building codes. Most of the additional requirements were based on subjective post-earthquake observations and limited laboratory testing. Starting in early 2000s, the major suspended ceiling manufacturers in the US have undertaken shake table testing of a number of ceiling installation. A majority of the test results had been proprietary and have focused toward specific installations produced by a given manufacturer. This was followed by large scale testing in both the US and Japan to investigate the response of ceilings as part of the building environment and assess the viability of tests conducted by manufacturers on smaller test frames. Separately, testing, and evaluation of suspended ceilings have been completed by authors and presented in this paper. The discussed testing comprised both quasi-static and shake table experiments. The testing used a large array of instrumentation to correlate the findings to member capacities.

Being a relatively young industry in the US, the utility-scale wind industry has recently started to produce domestic design documents—standards and guidelines—to better coordinate requirements of the US building codes with the international (European) standards in dominant use throughout the wind industry. While wind farm tower structural analysis and design are becoming more and better documented, this paper will attempt to go yet further into unknown and undocumented tower structural engineering topics as encountered in daily practice. Examples of such topics with little or no treatment in the engineering literature include the causes and repairs of tower dents, flange gaps, and splice bolt fatigue failure. Also discussed are unresolved questions regarding mysterious out-of-round creep of tower sections and whether conventional transport methods could cause tower damage. This paper’s target audience includes stakeholders in the utility-scale wind energy industry, specifically: (1) structural design professionals; (2) project/construction managers; (3) plant operations and maintenance managers; (4) engineers involved in tower transport or erection; and (5) subsets of the aforementioned groups involved in code and standards development. This paper has the following learning outcomes: (1) to provide examples of typical tower damage and their repairs; (2) to provide a glimpse of tower structural engineering practice issues that are seldom documented in the industry literature; and (3) to describe unresolved issues as a first step for more industry discussion.

Precast concrete products such as sumps, culverts, and trenches within truckable sizes are commonly used in industrial plants because they can be easily shipped and installed. For larger process sumps and tank foundations, the design of precast concrete segments can be unique and challenging in that additional considerations become necessary for size and weight effects, shipping, water stop detailing, connections between segments and installation sequence. Large diameter cylindrical storage water tanks are typically supported by a concrete ring wall foundation. Large process sumps typically are rectangular concrete boxes with structural steel platforms supporting vertical pumps and include one or more pipe penetration through the walls. Because sumps are positioned mostly below grade, the effects of unbalanced lateral soil pressure, and grade slope need to be considered. Traditionally, such tank and sump foundations are constructed on site using cast-in-place procedures, which are often impacted by weather conditions, labor resources and concrete batch plant capability. Utilizing precast concrete foundations can minimize these effects, control the product quality better and reduce labor cost. This is particularly suitable for a project located in a remote and weather-sensitive area. This paper addresses the design challenges of two large process sumps and one water tank foundation using segmental precast concrete construction for a project located in eastern Russian. Design considerations include the effects of a high seismic zone, thawing permafrost, waterproof joint design, transportation, and lifting loads, as well as conformance to Russian design codes. Additional considerations include constructability, transportation weight and size limits, precast contractor location and capabilities, seasonal construction periods, and the sequencing of installation.

Unitized curtain walls have become increasingly popular because of characteristically short lead times, high quality, and efficient installation as compared to traditional building envelope enclosures. Of course, these advantages are predicated on the proper integration with the base building structure. The Structural Engineer of Record (SER) and the façade Specialty Structural Engineer (SSE) often have limited opportunities to collaborate. This paper is written from the perspective of a custom curtain wall façade contractor intending to further the understanding within the structural engineering community of the design and performance of unitized curtain wall. Understanding the behavior of the façade system will aid the structural design community to develop structures that economically incorporate curtain wall attachment details and take advantage of and accommodate nuances of unitized curtain wall in the design, analysis, and detailing of the structure.

Applications of seismic isolation for essential equipment and components are limited and experimental evidence on the effectiveness of seismic isolation system for protection of equipment in multistory buildings is lacking. The paper includes the developments of experimental studies to assess the effectiveness of lead-rubber isolated platform for the seismic protection of simulated equipment under both horizontal and vertical floor seismic excitations. A scaled earthquake testing program includes a variety of floor accelerations of multistory buildings. A lead damper was introduced into the platform to achieve additional energy dissipation in the system. This paper presents: (1) a summary of the experimental settings of earthquake simulation tests; (2) sample of experimental results; and (3) a discussion on the effectiveness of lead formation to increase the energy dissipation capacity of the isolation platform.

The latest ASCE report “Wind Loads on Petrochemical and Other Industrial Structures” acknowledges some international documents and resources that guide the practicing engineer who is involved in reviewing designs or analyzing wind loads on structures at international Petrochemical facilities. Despite the consensus and increased uniformity in wind load determination within the profession, engineers are frequently confronted with situations where multiple country standards are required to be used for the same project. This presents significant challenges to designers, caution is required when applying and interpreting multiple codes and standards. This paper describes a comparison of design wind load calculations for pipe rack structures based on seven major international codes and standards: ASCE 7-2010 (American), AS/NZS 1170.2 2011 (Australian and New Zealand), EN Eurocode 1 2010 (European), GB 50009 2012 (Chinese), IS 875 2008 (Indian), NBC 2010 (Canadian), and SP 20.13330 2011 (Russian). A parametric study of a pipe rack module located in non-hurricane area supporting piping, electrical cables and equipment is presented. This simple case study highlights comparative approaches and data among the selected standards. Recommendations based on the study findings and the application of standards in wind loads on pipe rack modules are provided.

The goal of this study is to investigate the effects of coupling beam strength and stiffness on system performance for concrete building systems ranging from 35 to 40 stories. Specifically under investigation is the interaction between concrete core walls and coupling beams when the structure is subjected to earthquake ground motions. ASCE 41 recommendations for diagonally reinforced coupling beam strength and stiffness values are conservative and engineers often use alternate values for nonlinear analysis. This study assesses the impact of varying coupling beam strength and stiffness over a wide range of practical values on the global behavior of the structure. Multiple Engineering Demand Parameters including core wall shear, inter-story drift, and coupling beam chord rotation are used as metrics for investigating the global behavior of the coupling beam strength and stiffness on system performance. Results show that coupling beam chord rotation is sensitive to changes in strength and stiffness, whereas core wall shear and interstory drift remain relatively unaffected by these changes.

This paper presents the results from a recent experiment of a novel grouted Type III splice for reinforcing bars in gap-opening joints of seismic precast concrete structures (e.g., joint between a precast wall panel and the foundation). Section 18.2.7 of ACI 318-14 allows Type II splices for reinforcing bars at any location in a building, including yielding energy dissipation (ED) bars in plastic hinge zones. However, the certification requirements for Type II splices in the U.S. do not match the high cyclic strain demands that are possible in gap-opening precast concrete joints under extreme seismic loading. The use of short grouted splices simplifies the construction of these structures because protruding bar lengths from precast members can be minimized and field grouting lengths can be reduced. The experiment was conducted with the primary objective of developing a high-performance, but relatively simple, non-proprietary splice that can allow ED bars under cyclic loading to reach close to their full ultimate strength and fracture strain capacity over a short grouted development length. The tested bar, which was subjected to cyclic tension loading inside a tapered-cylindrical grouted splice, fractured (without pullout) during the 5th cycle to a maximum strain of 0.90ϵ_su, where ϵ_su is the measured monotonic strain capacity of the bar at peak strength. This result demonstrates that ED bars with tapered-cylindrical grouted splices can achieve similar performance as bars with fully-embedded development lengths.

This research presents methods to control vibration of suspended bridges decks by incorporating a self-centering friction damping mechanism to (1) mitigate damaging ambient vibrations and (2) maintain a necessary potential of energy dissipation during major seismic excitation. To achieve this, a thorough investigation of the relationship between viscous and friction damping is conducted both analytically and in a numerical computer model. The objective of this paper is to introduce friction damping concepts as well as methods of approaching equivalent viscous damping. Necessary design parameters for friction dampers will be identified and compared to that of their viscous damping counterpart in an effort achieve equal energy dissipation. Furthermore, this paper introduces the modified self-centering friction damping brace (SFDB) and discusses the concept of design and analysis for replacement of viscous dampers in suspended bridges. The modified SFDB is analyzed in a single degree of freedom system and compared to a typical viscously damped system. The free vibration behavior of the modified SFDB is compared to viscous damping behavior and evaluated for future research involving the retrofit of the Vincent Thomas Bridge in San Pedro, CA.

Metal plate connected wood trusses (MPCWT) are not designed to carry out-of-plane loads and performance of MPCWT assemblies under these loads are not considered. The goal of this research is to compare structural analysis models of MPCWT assemblies under out-of-plane loads to previous experimental data. The rotational stiffness of truss-wall connections, and truss bracing elements were evaluated for inclusion in the structural analysis model. A parametric study considering load location, joint stiffness and dimensions of MPCWT assembly was conducted. The structural analysis model of the MPCWT assemblies had first truss deflections within 4% difference of experimental results. Variation of the load location along the length of the MPCWT assembly produced a 9% difference in maximum deflection. The rotational stiffness of lateral and diagonal bracing should be included as model inputs for the accurate representation of experimental behavior since neither pin nor rigid assumptions were not correct.

Several studies have shown the vulnerability of buildings to sudden changes in lateral stiffness and strength, as in the case of a soft-story mechanism, which can cause damage or even collapse during strong earthquakes. This paper investigates the possibility of improving the seismic performance of soft-story structures by incorporating gyro-mass dampers (GMDs) as a novel alternative solution. GMDs are newly developed passive control devices. They generate a force that is proportional to the relative acceleration applied at their end nodes. The introduction of GMD elements increases the lateral capacity of the first story and the fundamental period of the entire structure. It also reduces the input energy of the earthquake ground motion. To evaluate the effectiveness of these devices, different configurations are proposed and time history analyses are performed.

The John B. Hynes Veterans Memorial Convention Center (Hynes) in Boston, Massachusetts, spans over the Massachusetts Turnpike (Turnpike), which carries eight lanes of traffic to and from the heart of the city. A 4 in. thick suspended reinforced-concrete-ceiling slab constructed in the early 1960s comprised a total of 42,000 sq ft (weighing about 1,000 tons) and separated the underside of the Hynes from the Prudential Center Tunnel (Tunnel) below. The owner, the Massachusetts Convention Center Authority, maintained the slab and performed regular maintenance, rehabilitation, and repairs. Over a 50 yr life, the slab deteriorated due to corroding reinforcement, and had effectively reached the end of its useful life. Removal, however, required construction sequencing that worked around limited nightly lane closures and limited weekend tunnel shutdowns. This paper discusses how the team effectively managed limited roadway access and tight working conditions to prepare the slab for removal, the controlled-demolition approach, and challenges encountered throughout the project.

In the aftermath of the 2010 Haiti earthquake, households were often reluctant to reoccupy their dwellings due to concerns about the safety of damaged structures. If feasible, structural repair (to complement to temporary sheltering) is a realistic option for rapid reoccupancy as reconstruction poses greater barriers of cost and time. Considering the economic and technological limitations found in developing regions, this paper addresses the question of whether it is feasible to repair a severely damaged substandard CM wall in a context-sensitive fashion, that is, using: (a) materials that are locally available and commonly used and often substandard (e.g., low-strength concrete and mortar); and (b) construction and installation practices that are familiar to local workers, without the need for additional training. Two full-scale CM wall specimens were subjected to cyclic quasi-static in-plane load test till failure, and re-tested after repair by means of reinforced plaster made of low-strength mortar and steel welded wire mesh. Three-dimensional digital image correlation was used to provide full-field strain maps to describe the load-resistance mechanisms and damage evolution. It is shown that the failed CM walls can be transformed into walls with acceptable strength and deformability. In addition, it is shown that only the repaired specimens qualify as earthquake-resistant structures based the acceptance criteria set forth in Mexico City Building Code for Masonry Structures (NTCM 2004). It is concluded that it is feasible to repair a highly-damaged substandard CM wall in a context-sensitive fashion and make it safe, comparable to a CM wall built with acceptable materials and details.

In the 2010 National Building Code of Canada (NRC 2010), certain structures can be designed for seismic loads using an equivalent static force procedure. In these provisions, elastic design forces are reduced by a ductility factor, R_d, which accounts for the ability of different systems to deform beyond yielding. The NBCC 2010, however, only provides ductility factors for traditional structural systems, including timber- or steel-based systems; there are currently no specific R_d factors for hybrid structural systems. Thus research is required to safely and efficiently design novel systems within the existing seismic design provisions. The FFTT system, an acronym for “Finding the Forest Through the Trees” is an innovative building system proposed for high-rise timber-steel composite structures using mass timber panels connected with steel beams. This research presents nonlinear dynamic analyses to propose an R_d factor for design Option-1 of the FFTT system considering the uncertainties of structural mass, hold-down stiffness, and connection properties of the lateral load resisting system. Based on the analyses presented herein, a ductility factor of 5.0 is deemed reasonable for design Option-1 of the novel timber-steel hybrid system.

Studies of seismic behavior of non-planar wall-to-beam joints are limited in the available literature. Furthermore, ACI 318-11 provisions are incomprehensive with regard to seismic detailing of these joints. The common practice is to provide a concealed column and/or a concealed beam where a gravity beam frames into the web of a structural wall. This research, as part of a broader experimental study, is meant to assess the performance of these joints and the impact of concealed columns on the overall performance of these joint. To accomplish these objectives, three half-scale RC interior beam-wall joints are investigated. Applicability of four available RC beam-column joint shear strength models is examined. Results from these models are compared. Also, effective joint shear area of non-planar wall-to-beam connections is studied.

In the past earthquakes, steel moment resisting frames suffered damage. Earthquake-induced damage in the main structural members, such as beams, and columns, leads to permanent deformations in buildings. The resulting permanent damage following earthquakes substantially increases repair costs. The repair of damaged buildings with extensive permanent deformations may not be economically feasible. Therefore, it is essential to eliminate the residual deformations while designing ductile beam—to—column connections. The seismic performance of steel buildings can be improved by allocating pre-specified elements in the building so as to dissipate the input energy and also provide self-centering (the ability to return the structure to its undeformed position). This paper presents a feasibility study of utilizing superelastic Shape Memory Alloy (SMA) plates in steel beam—column connections. Three-dimensional finite element models of steel beam—column subassemblies are generated to assess the efficiency of SMA-plates on the seismic behavior of connections. In this new application, SMA-plates are used in the plastic hinge region of the beam. The results of these finite element simulations are promising. The proposed connections with SMA plates could return to their original positions, while exhibiting a ductile behavior with good energy dissipation. Furthermore, the occurrence of local buckling in beam flanges was prevented in the new connections with SMA-plates.

Slip-critical connections have long been used in steel structures where joints are subjected to fatigue and joints with oversized and slotted holes. The understanding of the behavior of these connections through experimental testing has resulted in limited maximum slip coefficients with extensive surface preparation. The use and development of high performance surface coatings (HPSC) is one possible route to greatly increase the strength and promote construction using slip-critical connections. In this study a HPSC is developed which is economical and easy to apply. The experimental program preliminarily characterizes the formulation development of the HPSC. Particle size distribution and density of the HPSC are varied. From simple shear tests of activated HPSC on steel plates, analysis of the results indicate that HPSCs provide more stable and predictable behavior than unfinished or mill scale surfaces. Recommendations are made for continued development based on the preliminary results of this study.

Under real fire conditions, creep becomes a dominant factor and influences fire resistance of structural steel members. In this paper, the effect of high temperature creep on fire response of structural system is investigated. Phenomenological (rheological) creep models for materials with non-invariant properties are discussed here. The behavior of steel material at elevated temperatures is expressed in form of a constitutive equation. New probability-based and deterministic models describing the behavior of time-dependent materials are presented. The Gauss-Legendre method is used in order to obtain the solution of the viscoelastic integral equation. The review of literature clearly indicates that the creep effect on the structural fire response did not receive much attention. This study indicates that neglecting high temperature creep in fire resistance analysis of steel structures can lead to non-conservative predictions. The results are supported by step-by-step practical design examples and should be useful for practicing structural and fire protection engineers, code developers as well as researches and university faculty personal.

In 2015, the American Iron and Steel Institute (AISI) will issue a 2nd Edition of the Design Guide for Cold-Formed Steel Purlin Roof Framing Systems “Design Guide”. With the increased popularity of standing seam metal roofing and emphasis on sustainability, purlin supported roof systems are experiencing increased penetration into the conventional building market. For engineers who are accustomed to designing with hot-rolled steel, there are several additional design checks that must be performed. Notably, there is significant interaction between the sheathing and secondary purlin members, so the roof framing must be truly analyzed as a system. Additional checks thus are required to ensure force transfer through the system and overall system stability. Several important changes have been implemented in the second edition of the Design Guide. The Design Guide has been merged with the AISI Guide for Designing with Standing Seam Roof Panels requiring an overall restructuring. It includes an expanded section on diaphragm considerations related to purlin stability. It has been updated to include discussion and design examples of strut-purlins. Also new to the second edition is a discussion on discrete bracing for stability and the merits for using it as a design strategy.

The ASCE’s 2013 Report Card for America’s Infrastructure assigned in-service bridges a score of C+. This rating reflects the extent of the deteriorating conditions and deficiency of the national aging infrastructure network. Currently, transportation agencies depend heavily on experiential-based practices to make decisions regarding maintenance and preservation. While practitioners and decision-makers already invest ample efforts towards this cause, the lack of a rational understanding of system-level behavior of in-service structures makes resolving the problem even more complicated. This constraint, coupled with limited resources and the vast network of existing structures in service, highlights the need to develop strategies to better understand the operational safety and remaining life of these structures. In pursuit of this objective, this study focuses on understanding the performance of deteriorated prestressed concrete bridges. A performance-based assessment framework was developed, which allows for the integration of the various sources of damage within the primary load carrying members. This framework is then used to quantify the implications of these mechanisms on the serviceability, capacity, and remaining service life of the structure. The investigation, conducted using a numerical analysis platform, is expected to help support the maintenance decision through rational and risk-based techniques, which will ultimately integrate condition-based system behavior.

Jet Blast Deflectors (JBD) are safety structures that deflect and redirect high speed exhaust from a jet engine to prevent damage and injury to structures, aircraft, and people behind the JBD. These structures must be strong enough to withstand the high speed jet exhaust and wind loads and, at the same time, must be frangible if the JBD is in the Runway Safety Area (RSA) in order to minimize aircraft damage during accidental collision between the airplane and the JBD. Jet blast deflectors can take many shapes and forms and range in complexity from stationary concrete, metal, fiberglass systems, to movable systems that are controlled by hydraulic arms. This article discusses the analysis and design approach implemented in the design of a JBD system installed in one of the largest airports in the nation. The JBD is installed at the end of the runway in order to protect a nearby taxiway located at about 48.8 m (160 ft) away from the JBD. The configuration of the system was developed to satisfy, among other requirements, the frangibility criteria of the FAA guidelines. All components of the JBD, except for the connections, were made from Glass-Fiber Reinforced Polymer (GFRP), a frangible material. Connections were bolted using stainless steel fasteners. Computational Fluid Dynamics (CFD) and High-Fidelity, Physics-Based (HFPB) finite element simulations were undertaken to fine-tune and optimize the design of the JBD. The main goal of the optimization process was to minimize air speeds at the protected taxiway and ensure frangibility of the proposed design.

This paper presents preliminary results of an ongoing analytical study on the behavior of steel shear connections subjected to fire. Fire safety in building design has become a recent concern for researchers in the past few years. Steel beam-end connections affect significantly the overall performance of structures at elevated temperatures. Several experimental studies have been conducted on full scale beam-column assemblies; however, many aspects of the structural behavior and failure mechanisms that govern the behavior of steel beam-end connections at elevated temperatures are still not well characterized. The preliminary analytical program consists first of a series of finite element (FE) simulations of steel shear endplate and double angle connections that are conducted to better understand the behavior of end-plate and double angle connections at elevated temperatures. Second, the FE models are validated against experimental results of shear endplate and double angle connections at ambient and elevated temperature available in the literature. A comparison is also made between the capacity predictions of the two connections at ambient and elevated temperature. The FE models are capable of predicting the behavior of double angle and shear endplate connections under varied loading conditions and elevated temperatures. The results show that rotational ductility and capacity of the double angle at ambient and elevated temperature are both larger than that of the shear endplate connection.

The American Association of State Highway and Transportation Officials (AASHTO) Specifications provide simplified formulas to determine Live Load Distribution Factors (LLDFs) for timber girder bridges with timber decking. The AASHTO formulas have been developed based upon the parametric study for timber bridges subjected to typical highway vehicles. However, the majority of short span timber bridges are located on secondary roadways where agricultural vehicles often operate. These vehicles have more vastly different configurations and weights relative to highway vehicles; thus, they can result in more different LLDFs than highway vehicles. Hence, the focus of this study is on the investigation of agricultural vehicle induced LLDFs for a short span timber bridge with timber decking through field tests, simulations, and AASHTO-based codified methods. The bridge was tested with four heavy agricultural vehicles and a highway truck. Commercially available finite element analysis (FEA) software was used to generate an analytical model of the bridge. The model was refined with field data to replicate field responses and analytical LLDFs of the bridge. To account for uncertainties in agricultural vehicle parameters, a large number of agricultural vehicles with different characteristics in use in the United States were used as input loads in the model. Field and analytical LLDFs were compared to those obtained from the AASHTO-based codified methods. Findings indicated that the field and analytical LLDFs for most girders occasionally exceeded the AASHTO codified values.

Current seismic performance methodologies such as FEMA P-58 already have the ability to estimate the direct loss and indirect loss of buildings due to earthquakes using performance based earthquake engineering (PBEE). However, earthquake aftershocks, which have the potential to cause additional damage to buildings, are still not considered in these methodologies. On the other hand, previous seismic performance assessment considering aftershocks cannot account for various post-quake decisions (e.g. evacuation, safety evaluation, and repair), and have been based on simplified models which do not have the capacity to simulate many details. In this study, the effects of aftershocks and post-quake decisions on seismic performance are discussed, and an assessment methodology in accordance with other PBEE based methods that also has the ability to consider aftershocks was developed. As a case study, two reinforced concrete frame buildings are adopted for loss estimation using the proposed method. Eighteen near-fault and 60 far-field recorded mainshock-aftershock sequences are employed in the example. The direct loss and indirect loss (downtime and fatality loss) were investigated and show that significant difference may occur in seismic performance when comparing the scenario with and without considering aftershocks.

Dry cask storage systems (DCSS) are currently the only means of waste nuclear storage in the United States. Although these structures are designed for temporary use with an intended service-life of 20 years, in the absence of a long-term storage solution, it is highly likely that DCSS will be used for a period exceeding 50 years. Approximately 40% of all the DCSS employ a reinforced concrete (RC) outerpack for protecting nuclear waste against manmade and natural hazards as well as for radiation shielding. As such, it is essential to investigate the durability performance of the RC under environmental and mechanical conditions specific to DCSS. One of the main durability issues is identified as the corrosion of reinforcement. High temperature from the nuclear waste, ambient humidity and potential airborne chloride at the storage site increases the risk of corrosion in these structures. In this paper, two different mixtures are studied, a control mixture meeting the current specifications for DCSS and a mixture with added calcium chloride. The second mixture is intended to accelerate the corrosion for the two-year period of the experimental program. As a part of an ongoing experimental program, specimens are being tested at different ages to measure compressive, tensile and flexural strength, and mass loss due to corrosion, among others. It is expected that the results from this experimental program will help understand the long term behavior of RC DCSS.

Dynamic analysis was required for a motor and its 18.6 m (61 ft) × 4.3 m (14 ft) × 5.2 m (17 ft) (length × width × height) reinforced concrete table top support. Motor power rating was 17.2 MW (23 300 hp), weight 388 kN (43.6 ton) and nominal operating speed 1800 rpm. Governing document was API 546. Provision for motor-structure interaction was the key element of the finite element model; motor, not structure, responses were at issue. Motor rotor journal displacement was well below the API 546 limit, even though a dominant natural frequency was within the normal operating range. Though low modes were governed by columns, the dominant mode in the operating range was governed by strong-axis flexure of the 1070 mm (42 in) thick table top. The higher mode was self-restraining so the resonance condition was well controlled. The motor-structure system was judged compliant with API 546.

On a recent project, the authors investigated a commercial structure roof that was fabricated using a Light Gauge Metal Truss (LGMT) system and was experiencing distress shortly after construction. An investigation into the cause of the reported distress revealed extensive construction-related damage to the LGMT system supporting the roof. The subsequent necessary analysis of the as-built LGMT system also identified design-related deficiencies that required repairs. This paper focuses on the authors’ observations and challenges during the project and offers considerations that engineers can use when evaluating the practicality of LGMT on certain projects.

Topology optimization has recently been explored as a tool for the conceptual design of efficient structures during the initial building design stage. Although these techniques were originally developed in a deterministic setting, most practical applications are subject to inherent uncertainties in the design problem (e.g. stochastic loads, model idealization) and thus there has recently been an effort to incorporate the effect of these uncertainties into the topology optimization procedure. Within this context, the authors have developed an approach that is able to efficiently account for the uncertainties in the problem at hand using concepts from Performance-Based Design. This paper presents a general overview of this method and illustrates its applicability for the topology design of structures under wind and seismic hazards.

The superelastic shape memory alloy (SMA) rebar can significantly improve the seismic performance of reinforced concrete (RC) structures. This study was motivated from a blind prediction contest of a full-scale 7-storey RC shear wall building at the University of California, San Diego. A finite element (FE) analysis was conducted to investigate the seismic performance of RC shear wall with the application of SMA rebar. The SMA rebar was applied at the plastic hinge location of the shear wall only and the steel rebar was used for all other sections. The seismic performance of shear wall was evaluated by performing incremental dynamic analysis (IDA) using 13 ground motions. The seismic demand was recorded in terms of inter-storey drift ratio until the full collapse of the building. The safety of the wall was measured in terms of collapse margin ratio (CMR) explicitly considering the uncertainty. The results show that the SMA rebar significantly improved the performance of the shear wall building and yielded higher CMR as compared to the conventional RC building.

Conventional braced frame systems have limited drift capacity prior to brace buckling and related damage leads to deterioration in strength and stiffness. Rocking braced frame systems increase the drift capacity; however, significant higher mode effects and local yielding may result from column uplift. A friction-damped braced frame (FDBF) system with buckling-restrained columns (FDBF-BRC) is being developed to provide significant drift capacity while limiting damage and residual drift without column uplift. The FDBF-BRC system consists of beams, columns, and braces branching off a central column, and buckling restrained columns (BRCs) are incorporated into the system in the first story. The BRCs and friction generated at lateral-load bearings are used to dissipate energy to minimize the overall seismic response of the FDBF-BRC system. Vertically aligned post-tensioning bars provide additional overturning moment resistance and aid in self-centering the system to eliminate residual drift. In this study, a suite of 44 DBE-level ground motions used in FEMA P695 is numerically applied to several FDBF-BRCs to demonstrate the seismic performance of the system. The results show that the FDBF-BRC system has high ductility and energy dissipation capacity, and is an effective seismic resistant system.

Cross-Laminated-Timber (CLT) is increasingly gaining popularity in residential and non-residential applications in North America. To use CLT as lateral load resisting system, individual panels need to be connected. In order to provide in-plane shear connections, CLT panels may be joined with a variety of options including the use of self-tapping-screws (STS) in surface splines and half-lap joints. Alternatively, STS can be installed at an angle to the plane allowing for simple butt joints and avoiding any machining. This study investigated the performance of CLT panel assemblies connected with STS under vertical shear loading. The three aforementioned options were applied to join 3ply and 5-ply CLT panels. A total of 60 mid-scale quasi-static shear tests were performed to determine and compare the connection performance in terms of strength, stiffness, and ductility. It was shown that – depending on the screw layout – either very stiff or very ductile joint performance can be achieved.

Confining concrete columns with fiber reinforced polymer (FRP) is one the most effective methods to increase their strength and ductility. To have a reliable and economical design, the stress-strain behavior of FRP confined concrete under different types of loadings needs to be properly examined and the influence of parameters affecting this behavior should be considered. In this study, the results from previous experimental tests on FRP confined concrete prisms, including rectangular, square and cylindrical prisms, under the action of cyclic and monotonic loadings are reviewed and the effect of aspect ratio and corner radius on different aspects of cyclic and monotonic stress-strain behavior of these prisms is discussed. A statistical analysis is also provided and the accuracy of the presented monotonic models is evaluated. The results of the statistical analysis are very helpful for developing a stress-strain model.

For standard fire resistance design, the architect usually serves as the responsible party for satisfying code requirements for structural fire protection. As such, the architect typically selects qualified fire resistance assemblies from available listings, and the structural engineer may not have any influence in this regard. However, this long-standing paradigm is now starting to be challenged by engineers, contractors and approving authorities alike. In North America, the structural fire resistance of a steel frame is typically provided by the application of a passive fire protection material that has been qualified and listed based upon standard fire testing. Structural engineers are not conventionally trained in fire resistance design and may not be aware of the qualification process. Moreover, structural engineers may not be aware of the value that they could offer architects as it pertains to optimization of a fire resistance design. This paper explores the benefit of structural engineering participation in the fire resistance design process. It highlights associated design responsibilities and illustrates key considerations, benefits and limitations pertinent to fire resistance design. The American Institute of Steel Construction (AISC) provides a standardized methodology to assess robustness of structures in fire, including a load combination associated with an accidental loading scenario. A worked example within this paper illustrates the application of these methods within the context of the optimization of a fire resistance design. Fundamentally, the worked example considers a steel framed building, evaluates the load-bearing capacity of each member individually and evaluates performance in comparison to the failure criteria typically adopted within fire tests. Additionally, discussion is provided with respect to the viability of passive fire protection material and importantly, how the structural analysis can inform the steelwork specification to ensure an economic and up-front value-engineered optimized solution with advantageous impacts on construction sequencing.

The surface roughness of the earth has a significant effect on wind speed and the wind loading used in the design of structures. Surface roughness of the earth is defined by the terrain, landscaping, and man-built environment. The American Society of Civil Engineers Standard 7 (ASCE 7-10) Minimum Design Loads for Buildings and Other Structures provides general guidelines for classifying the terrain upwind of a structure in order to determine a structure’s design wind pressures. ASCE 7-10 identifies three exposure categories to cover the earth’s terrain. Because of the changing and inconsistent nature of our topography, selecting one Exposure Category often does not represent the actual surface roughness conditions adjacent to the design structure. While ASCE 7-10 offers guidance for adjusting the wind load design values between categories, the guidelines and equations are ambiguous and difficult to navigate. The ASCE guidelines and their origins are reviewed to aid in the understanding of the calculations currently used to determine the wind loading on a structure. The purpose of the study is to improve the calculation of surface roughness to provide more accurate design wind loading. The study explores expanding ASCE 7-10 code values for the velocity pressure coefficient to account for a wider range of surface roughness characteristics and transitions between exposure categories. Expanding the range of values for the velocity pressure coefficient will provide designers the opportunity to better specify the wind pressures on a structure. The study uses a geographic information system (GIS) aerial mapping program to map the surface roughness upwind of a structure located adjacent to changing and inconsistent terrain. By using GIS to map the terrain, a more accurate surface roughness can be calculated eliminating the uncertainty and ambiguity that can occur when selecting one Exposure Category. This study caters to structural engineers and the refinement of design wind loads used in practical design of structures. As GIS and 3D modeling continue to develop, GIS mapping could represent the next generation of analysis. The study is part of master’s thesis work at the University of Colorado Denver.

Many buildings in the U.S. are vulnerable to natural and man-made disasters due to the increased popularity of sustainable building infrastructure. Life cycle assessment analyses are required to design and achieve “green” building status. These analyses do not require evaluations of building performance during natural or man-made hazards. Increases in labor and material caused by robust and resilient systems also often increase embodied energy and carbon dioxide emissions. Those LCA analyses which do consider seismic performance of a building many times do not take into account the seismic performance of the non-structural secondary systems (partition walls, drop ceilings, etc.). In the particular case of fire hazards, automatic sprinkler systems add 30-40kg of embodied carbon to a building; however, reduce the risk factor for fire during the life span of a building. To prevent post-fire repairs, which would increase the embodied energy and carbon of the building more, hazard mitigation needs to be integrated with sustainability. The development of performance-based design standards helps this integration; however, the lack of risk factors incorporated into life cycle assessments needs to be remedied, not just for seismic design, but all natural disasters. This paper references previous developments in the marriage between natural hazard mitigation and sustainability as well as the limitations of the tools available to structural engineers. Advancements in the development of a risk factor for fire is discussed as well as the increased carbon emissions and embodied energy of buildings without active fire protective measures.

Although prohibited, artifacts such as fasteners, welds, notches, and other defects commonly occur in the plastic hinge region of constructed special moment resisting frame (SMRF) beams. Full-scale moment connection tests are a cost prohibitive means to investigate the wide range of artifact types and locations. A new approach is developed to evaluate the effect of powder actuated fasteners, notches, and welds on low cycle fatigue behavior of steel moment frames. A total of forty-eight cyclic bend tests and monotonic axial tests have been conducted with six types of specimens including bare specimens with no artifacts, powder actuated fasteners, puddle welds, ground fillet welds, notches ground to taper, and notches filled with weld and ground smooth. These types of fasteners and repair methods represent typical connection of nonstructural elements such as partition walls, pipe racks, ductwork to the structural steel, and repair methods described in AWS D1.8. No previous testing data exists as to how these repair methods affect the low cycle fatigue resistance of steel sections. The applied inelastic strains approximate those at local buckles in full-scale tests.

Timber-Concrete Composite (TCC) systems have been employed as an efficient solution in medium span structural applications; their use remains largely confined to European countries. TCC systems are generally comprised of a timber and concrete element with a shear connection between. A large number of precedents for T-beam configurations exist; however, the growing availability of flat plate engineered wood products (EWPs) in North America has offered designers greater versatility in terms of floor plans and architectural expression in modern timber and hybrid structures. The opportunity exists to enhance the strength, stiffness, fire, and vibration performance of floors using these products by introducing a concrete topping, connected to the timber to form a composite. A research program at the University of British Columbia Vancouver investigates the performance of five different connector types (a post-installed screw system, cast-in screws, glued-in steel mesh, adhesive bonded, and mechanical interlocking) in three different EWPs (Cross-Laminated-Timber, Laminated-Veneer-Lumber, and Laminated-Strand-Lumber). Over 200 mid-scale push-out tests were performed in the first stage of experimental work to evaluate the connector performance and to optimize the design of subsequent vibration and bending testing of full-scale specimens, including specimens subjected to long-term loading.

Material properties of structural steel alloy are variable. Variability may be observed in engineering parameters such as yield stress, modulus of elasticity and strain hardening modulus of the structural steel. Such variability may affect the seismic response of the steel structures. This research study focuses on use of scientific workflows using the Pegasus workflow system, which is available on the NEEShub (nees.org) as an OpenSees Laboratory tool (nees.org/resources/openseeslab) and can provide access to supercomputing resources through the Open Science Grid (OSG), to investigate the possible effects of steel engineering material properties on the simulated seismic response of a steel special moment resisting frame (SMRF). The Pegasus workflow system is used to develop a four-story four-bay steel SMRF model to run on OpenSees (opensees.berkeley.edu). The Pegasus workflow accepts separate coefficients of variation for steel yield stress, modulus of elasticity and ratio of modulus of strain hardening to modulus of elasticity of steel. The workflow then generates different material properties randomly within the defined ranges of the variability. These random material properties are then assigned to the girder and column elements of a series of steel SMRF OpenSees models. The response of these steel SMRFs to various earthquake ground motions are simulated using the OpenSees simulation platform. The output of the simulations are compared in terms of maximum roof displacement, the maximum story drift anywhere in the structure, the maximum roof acceleration response, and the maximum base shear demand. Individual and combined material engineering property variations are compared with results obtained from the reference structure that has no variation in its material properties and for which mean values the material properties are used. It is observed that variability in modulus of elasticity of steel, variability in combinations of modulus of elasticity and yield stress, and variability in yield stress respectively resulted in the highest variations in roof drift, story drift and base shear while variability in the modulus of strain hardening had minimal effect.

Throughout the United States, wireless communication service providers (carriers) mount their antennas to existing water towers, in lieu of constructing their own dedicated structures. With the rapid increase in cellular data consumption and the expansion of coverage, carriers are progressively adding new as well as enlarging existing antenna assemblies. Despite this continuing trend, the standards to which these towers are designed (American Water Works Association AWWA D-100 and AWWA D-103) give little direction on how to address the increase in wind load to the tower structures resulting from the addition of this excess equipment. Though the AWWA standards provide explicit guidance for the design and analysis of the water tank, tower legs, and bracing, the added effects of appurtenances and cellular antenna structures is largely unclear. Therefore, structural engineers have resorted to other standards: the Telecommunication Industry Association (TIA 222-G), American Society of Civil Engineering (ASCE 7-10), and American Institute of Steel Construction (AISC 360-10). However, because AWWA standards exist independently of, and are not referenced by, the International Building Code (IBC), there is little interface between current practices and AWWA provisions, leaving little to guide overall analysis/design of tower additions. This has led to the use of loose and irregular code interpretations, leading to inconsistent outcomes, increased costs, and lost man hours. This paper presents a comparison of multiple design procedures used to mount telecommunication antennas to existing water towers and makes recommendations for a cohesive design methodology to guide and improve current practices.

This study aims to investigate the skewed extended shear tab connections’ behavior. In order to achieve the goal of the study, finite element models for orthogonal configuration were generated using the finite element analysis software ABAQUS. Results were compared with their counterparts obtained from experimental testing to verify the finite element models. Then, finite element models were skewed at different angles, results obtained from skewed configuration were compared with orthogonal results. It was observed that the skewed and the orthogonal configurations have the same failure models, however, the twist of the shear plate increases with increase of the connection’s orientation due to the additional twisting moment transferred from the supported beam to the supporting member. Additionally, it was found that the connection’s vertical displacement is independent from the connection’s orientation. The relationship between the connection’s twist and the skewed angle was investigated, it was observed that this relationship can be represented using a linear equation. This equation was utilized to derive an equation that relates the skewed and orthogonal connection’s twist. The proposed equation can be used to modify the plate required shear strength and the plate torsional strength equations in the AISC manual 14th edition in order to determine the need for stabilizer plates.

The major difficulties faced with traditional structural bracing systems against seismic loading include compression buckling and permanent residual deformation under seismic loading. Once buckling occurs, the strength and stiffness of a brace gets significantly reduced and the stiffness degrades rapidly in subsequent load cycles. A significant number of researches have been conducted in resolving this issue and various ideas have been proposed and developed for the industry, e.g. buckling restrained brace, cast steel yielding fuse, SCED, MANSIDE, and RHDB braces, etc. Unfortunately, most of these solutions are expensive and complicated to construct. Authors here have proposed a novel approach in addressing this issue using a modification of a device commonly seen in mechanical systems, which is a cylinder-piston assembly. In this system, stiffness and re-centering are contributed by shape memory alloy ties. This study investigates the behavior of this innovative Piston Based Self-Centering (PBSC) bracing system in finite element environment. Utilizing this assembly, a brace member is able to carry large magnitude of tensile and compression loading without buckling. Furthermore, this brace is able to re-center after large nonlinear deformation. This paper presents the results of the analytical investigation carried out in ABAQUS software using finite element method. The load deformation hysteresis was determined and a flag shaped hysteresis was achieved, which indicates good re-centering capability of the proposed system.

A design method for Welded Column Splice (WCS) connections that feature Partial Joint Penetration (PJP) welds is presented. The method represents the culmination of a comprehensive program of material and large-scale testing, Finite Element Fracture Mechanics (FEFM) simulations, and reliability analysis. The primary motivation for the development of this method is to support PJP splices in seismic moment frames. Since failure of PJP splices is controlled by fracture at the unfused weld root, FEFM simulations that rely on elastic-plastic fracture mechanics (i.e., the use of the J-integral) and consider von Mises plasticity, along with large deformation response are used to parametrically examine a range of splice configurations. Results of the FEFM simulations are validated against previously published large-scale test data and are ultimately used to develop equations to characterize the strength of PJP WCS connections. Reliability analysis is used to formulate strength reduction (i.e.,φ) factors such that the design method may exhibit acceptable margins of safety.

Shear tab connections are considered amongst the most popular shear connections in design and construction. Low fabrication expenses and ease of assembly are the two key factors contributing to the desirability of this type of connection. In spite of the benefits, some problems appear in the construction of special cases. When the shear tab is intended to be framed into the web of a supporting column or girder, the flanges of the supporting element form an obstacle in field construction. To overcome this issue, one solution is to extend the shear tab beyond the supporting element flanges. This configuration is referred to as an “extended shear tab”. Although extended shear tabs are negligibly different from conventional shear tabs in terms of fabrication and erection costs, their behavior is significantly changed due to the considerably increased length. Moreover, instability issues may arise resulting from the increased slenderness. To investigate the behavior of extended shear tabs, a comprehensive research program consisting of both numerical and experimental studies has been defined. This paper outlines some of the results and observations acquired from the testing phase of the program, which is conducted on full-scale extended shear tab specimens. The test matrix is organized to investigate the effect of a number of connection parameters on the overall behavior of the extended shear tab connection. The parameters subjected to investigation in this paper include shear tab length, shear tab thickness and bolt configuration. The behavior of these specimens is studied in terms of connection capacity, failure mode and shear load eccentricity. Results of the tests together with those of the numerical modelling will be used to propose reliable and efficient guidelines for the design of extended shear tabs.

Steel Plate Shear Walls (SPSWs) are efficient and economical energy dissipating systems for buildings located in regions of high seismic risk. In spite of many benefits of SPSWs, however, their overturning stiffness is relatively low, especially in mid-to-high rise buildings. Therefore, there is a need for incorporating other structural elements in conjunction with such systems to resist high overturning moments resulting from lateral loads. A logical solution that can be effectively used in SPSW systems is to rigidly connect the girders of adjacent bays to the columns of SPSWs (on both sides) forming an interacting system of shear wall and moment frame in which the adjacent girders act as outriggers to reduce the overturning moments in the SPSW. However, insufficient information exists on behavior and efficiency of such structural system, herein referred to as SPSW with Outriggers (SPSW-O). As part of a comprehensive research project on SPSWs being conducted at the University of Alberta, this paper describes different potential SPSW-O options and discusses their effectiveness in improving the flexural stiffness of the system. The performance of these options is evaluated for 20-story SPSW-O systems using nonlinear static and response history analyses.

An analytical investigation is performed on the linked column steel frame system (LCF) and verified based on results from rigorous iterative design conducted for experimental frame. The LCF is a new lateral braced-free structural steel system intended for rapid return to occupancy performance level following a design level earthquake. The structural system consists of moment frames for the gravity system combined with closely spaced dual columns interconnected with bolted links for the lateral system. An analytical model is presented based on the mechanics of the system to evaluate the lateral stiffness of the LCF. The expressions developed may be used to select the geometric properties not only of the closely spaced dual columns but also the links, meeting the design inter-story drift limits. Analytically estimating the stiffness provides the designers with tools to size structural members and provide a first estimate of drift under earthquake loading, which is useful since the LCF system tends to be drift controlled.

The self-centering steel plate shear wall (SC-SPSW) combines the high lateral strength and stiffness of thin steel web plates, typically connected to beams and columns, with the recentering capabilities of post-tensioned (PT) beam-column connections to form a resilient structural system that sustains minimal boundary frame damage after severe ground shaking. To further improve structural economy, robustness, and constructability, a modified SC-SPSW with web plates connected only to the beams has been proposed as a means of reducing column demands and reducing localized strain demands in the web plate due to PT connection gap opening. Experimental and numerical investigations of SC-SPSWs with beam-only web plate connectivity have shown the beam-connected SC-SPSWs to have overall lighter steel weights, delayed onset and propagation of web plate tearing, and increased energy dissipation compared to SC-SPSWs of comparable strength with web plates connected to beams and columns. Results from these studies on SC-SPSWs suggest similar benefits from employing beam-connected web plates in conventional steel plate shear walls (SPSWs). This paper discusses the behavior of and design implications for beam-connected web plates in SPSWs and SC-SPSWs. Response of SC-SPSWs with beam-connected web plates from numerical models and experimental results are compared. Two three-story SC-SPSWs with beam-connected and fully-connected web plates was designed to have equal strength and the steel weight of each design is compared to address potential economic benefits from releasing the web plates from the columns. This research is of interest for university faculty and design professionals worldwide who focus on design of structural systems in high seismic regions. This presentation will provide design alternatives and highlight new research directions for improving economy, constructability, and resiliency of SPSWs.

Ductile fracture is a common failure mode of components under various loadings, which has recently been identified to be dependent on the first, second, and third deviatoric stress invariants. The fracture can typically be described in terms of the stress triaxiality and lode angle parameter. A newly developed ductile fracture criteria with the above two parameters is introduced, and based on which the fracture modes of the bolted gusset plate connections and hollow sections in gusset plate welded connections under quasi-static loading are simulated. The findings of numerical analysis are compared to experimental results, and acceptable correlations are achieved. The fracture modes, the block shear, and the fracture sequence are well-predicted by the proposed fracture criterion and simulated through finite-element analysis. The bolted gusset plate connections are discussed in detail since they include shear fracture, which is typically challenging to simulate. The influence of lode angle parameter (deviatoric stress portion) on the fracture phenomena is found to be significant and varies with stress states, as well as the stress triaxiality (hydrostatic stress portion). Suggestions on an optimization tool for this type of structure details are put forward based on simulation and experimental results. It is also shown that the newly developed ductile fracture model can be used by design engineers for predicting failure in steel structures under multi-axial stress states.

Steel plate shear walls (SPSWs) are a prevalent, internationally used lateral load resisting system. They have mainly been utilized in buildings in the United States, Canada, and Japan. However, despite their popularity, they also present a few challenges; their hysteretic behavior is pinched, the web plate has negligible stiffness during load reversals, and moment connections are required between the horizontal boundary elements (HBE) and vertical boundary elements (VBE). Ring shaped—steel plate shear walls (RS-SPSWs) are a novel structural system that offer improved seismic performance by mitigating the challenges of conventional SPSWs. A buckling study was performed on RS-SPSWs utilizing finite element analysis. The conclusions of the buckling study can be used to prevent lateral torsional buckling of the RS-SPSW rings, resulting in good hysteretic performance. This paper outlines how non-dimensional slenderness ratios, such as ring radius to ring width, ring radius to plate thickness, and ring width to plate thickness, affect the buckling behavior of RS-SPSW infill panels. The study concludes that the limiting rotation allowable in the quarter-arc segments of the rings before hysteretic performance starts to degrade is 0.08 radians. It was found that setting the ratio of ring width to plate thickness equal to 11 or less limits the quarter-arc ring rotation to be below the limit and lateral torsional buckling was prevented.

The cyclic behavior of baseplate connections has long been recognized to play an important role in the seismic behavior of buildings, non-building structures, and nonstructural components. However, the actual cyclic behavior of these connections is often grossly simplified in both static and dynamic analysis as either a fully pinned or fully fixed boundary condition. This approach may lead to over-conservative designs or under-prediction of drifts and other demands, depending on the actual behavior of the connection. A commonly cited reason for this simplistic approach is the sophistication and cost required to fully model these connections using finite-element techniques. This paper presents preliminary results from a semi-automated approach for performing parametric numerical analyses. The method provides estimates of the initial stiffness, secant yield stiffness, ultimate strength, and rotation capacity considering a variety of common baseplate and anchor configurations. These values are essential for designers performing hand calculations or as input to global structural models. The numerical model presented has undergone preliminary verification using results from recent full-scale testing, and utilizes material properties from commonly used anchor types and grades.

A new Linear Response History (LRH) analysis procedure has been approved for inclusion in the 2015 NEHRP Recommended Provisions, and will likely be included with some minor revisions in Chapter 12 of ASCE 7-16. The principal differences between the new procedure and the LRH procedure that is currently included in Chapter 16 of ASCE 7-10 are: 1) spectrum matched ground motions are required for seismic analysis, 2) the structure being analyzed is required to be modeled in three dimensions, 3) accidental torsion, where required, must be included in the analysis by offsetting the center of mass at each floor level, 4) P-Delta effects must be included directly in the analysis, and 5) peer review is not required. Additionally, requirements for scaling the results for consistency with the Equivalent Lateral Force seismic base shear demands are clarified.

This paper explores the inelastic behavior and the risk of collapse of buildings designed for wind loads. The approach used is similar to the prevailing method utilized for seismic loads (FEMA P-695). Single-degree-of-freedom models are used to represent the hysteretic behavior of the actual main wind-force resisting systems, including in-cycle degradation. An ensemble of wind load records from boundary-layer wind tunnel tests are applied to capture both along-wind and cross-wind effects. Wind loads are then scaled (intensified corresponding to increasing hazard levels) using an incremental dynamic analysis (IDA) approach until lateral instability and collapse occurs. The risk of collapse is quantified by incorporating epistemic uncertainty and integrating collapse fragility with ASCE 7-10 wind speed data.

An updated Linear Response History (LRH) analysis procedure has been approved to include in the 2015 NEHRP Provisions and is under consideration for inclusion in Chapter 12 of ASCE 7-16. This updated procedure differs somewhat from the LRH analysis procedures provided in Chapter 16 of the preceding code cycles with the primary difference being that recorded ground motions are adjusted for use in analysis by spectral matching. The idea behind this approach is to provide an analysis method that is similar in principle to Modal Response Spectrum (MRS) analysis, but due to direct addition of modal responses, preserves the sign (eg. tension or compression) of member actions and system deformations. To simplify the process of spectrum matching, an interactive computational tool called the Spectrum Match Toolkit was developed using the RSPMatch09 as the analysis engine. Available at no cost, this Toolkit is capable of simultaneously matching upto 3 pairs of horizontal ground motion components and provides the matched records in a form that is convenient for the subsequent response history analysis. This paper briefly discusses the new 2015 NEHRP provisions for LRH analysis, provides a summary of the theory behind response spectrum matching, discusses the implementation of the procedure using Matlab, and demonstrates some of the unique features of the Toolkit.

The increase in the number of seismic events and their devastations in the recent past has assisted in many developments in seismic codes of various international standards. Codes adopt conventional elastic methods in the design of structures to estimate the strength and deformation demand employing seismic design factors to represent the nonlinear behavior of the structure. Four typical high-rise steel buildings of 8, 12, 16 and 20 stories are designed and detailed using various seismic codes. Seismic response of the reference buildings is assessed with detailed fiber-based models using inelastic pushover and incremental dynamic analyses subject to 20 strong seismic records. The proposed study provides comparisons between different seismic design codes for the range of the reference buildings at different performance levels. This study may help the designers in optimizing their design in the seismic regions and provide an insight to assess the seismic performance and predict the behavior at different performance levels.

Several practical tools for the characterization of the optimal layout of material in a structure have been developed in recent years based on both numerical and analytical approaches. Within the analytical methods, optimal layouts can be based on specific geometric rules recently investigated in the literature. The resulting designs represents a stiff structure which requires ductile elements placed at strategic locations to minimize the impact of an extreme seismic event on the structure itself. This presentation will highlight a methodology to combine stiff optimal geometrical layouts with the use of ductile links in a high-rise building.

Design of base-isolated structures using the Equivalent Lateral Force procedure of ASCE 7 is limited to regular buildings with moderate ground motions. When the limits of the procedure are exceeded, nonlinear response history analysis is usually implemented to capture the dynamic interaction of the superstructure and the isolation system using site-specific ground motions. This paper provides an example of a hybrid approach for designing base-isolated structures by conducting a detailed nonlinear response history analysis of a simplified isolator-building system to generate an envelope of story forces to be used in the design of the building using a fixed-base, static analysis approach. This allows the engineer to take advantage of the potential reductions in base shear and maximum displacement permitted by a dynamic analysis while preserving the simplicity of a static analysis for design. The resulting vertical force distribution from the simplified model is also compared to the new vertical force distribution for isolated structures included in ASCE 7-16. Results of nonlinear response history analyses using the simplified isolator-building model provides the maximum isolator design displacement, forces for the design of the superstructure lateral system, and anchorage of nonstructural components. The analysis also applies tri-directional acceleration input (as a peer review requirement) in order to capture the vertical demands on the isolation system and building components, and the potential increase in lateral forces and accelerations due to coupled vertical-horizontal response of the selected isolator type. The system behavior using vertical excitation is compared to that of horizontal excitation only and both are compared to the proposed code vertical force distribution.

One of the most important attributes of our structural engineering profession is that it is highly creative. This creativity should be exploited endlessly by educators of the next generation of structural engineers because creativity leads to passion, which leads to inspiration, which leads to students learning almost everything they need to know themselves. This is true education for life-long learning, without boundaries. This paper attempts to demonstrate how this form of learning is possible within structural engineering education.

The ability of structural engineering educators to introduce to students complex 3D spatial arrangements typically has been limited to 2D drawings or physical models. To more fully explore all facets of a structure and better understand structural behavior at the member and system level, models undergoing different modes of deformation and failure are deployed in a virtual reality setting. The virtual reality environment developed allows users to interact with a structure through a head mounted device and hand system in a CAVE-like immersive environment or with a virtual reality headset such as the Oculus Rift. The use of a portable headset allows the virtual reality models to be directly accessible in the classroom. The models, which can be modified and expanded, enable students to view a wide variety of structures under different loadings from any number of vantage points unlike a physical model that may be limited by cost and safety concerns.

The reported study addresses the preparedness of the Masters-Level structural engineering graduate to enter the structural engineering profession. A framework of knowledge is presented which is based on the profession’s assessment of needs and their expectation of how these needs can be achieved by a combination of graduate-level academic work, early years in professional employment, and through lifelong learning activities. This study used a modified Delphi method utilizing e-mail-based surveys in three rounds involving 33 participants, most chosen to represent practice and with some from the academic and professional society communities. This paper presents some of the principal results of this study. The outcomes of the study are expected to provide very useful preliminary information for the structural engineering community and to help guide possible future activities by this and other professional communities in conducting similar studies addressing the framework of knowledge for their specific profession.

Although conventional structural analysis software is widely used by practicing engineers, its pedagogical value for students is limited, especially in design applications. Nevertheless, there is an established value in students exploring engineering problems through computational means. This paper presents alternative computational techniques and tools that are effective improvements upon structural analysis software in the university classroom. The first set focuses on graphic statics. The second involves interactive evolutionary optimization. The paper provides feedback about their effective implementation in classrooms and demonstrates how the new tools can continue to be used by students beyond the classroom, to expand explorative opportunities for conceptual structural design in practice.

Current engineering education places a significant focus on design of new, idealized structures. However, many graduating engineers are entering the workforce and are faced with evaluation of existing complex systems. To address this learning gap, a new graduate course was recently added at Tennessee Technological University titled, “Structural Identification of Constructed Systems”. Structural identification is the process of creating, then updating a physics-based structural model based on its measured static and/or dynamic measured response which is then used for evaluation of the structure’s performance as well as making critical decisions. The new course taught students the fundamentals of Structural Identification through hands-on experience, which included several laboratory experiments and projects. This paper presents the primary characteristics of the course along with sample student projects.

Architectural design relies upon structural design principles to help gracefully resist the stresses of building elements that enclose spaces. This discipline and expertise of integration typically takes years to develop but unfortunately, instead of teaching these skills side-by-side with coordinated expectations for escalating levels of expertise, representation, and analysis, these courses have frequently been separated from each other in architectural curricula. The oppositional pedagogical methodologies and differential expectations for development that occur as a result of this have adverse consequences for student learning and practical preparedness. This paper, intended for a national target audience of university faculty and practitioners, will outline a series of major curricular changes made to Iowa State University’s structural design course for architecture students which was explicitly reconfigured to address these concerns. Three specific lab assignments will be presented—one from the beginning, middle, and end of the new structural modules—to show how this new sequence has expanded and coordinated the range of curricular considerations within the structural coursework through the use of interactive, design-based learning activities and elevated expectations for course content. The paper will describe the critical aspects of the new curricular format and the corresponding innovations in learning activities in order to demonstrate how these three labs serve as benchmarks of demonstrated learning objectives in the sequence. Examples of student work will be shown, and an assessment of the efficacy of the assignments will be presented including reflections upon lessons learned and suggestions for future improvements.

The Bachelor degree of Civil Engineering in the University of Coruna has an elective course on Optimum Design of Structures since twenty years ago. That course allows the students to be aware of the meaning of structural design, the way to formulate optimization problems and the variants of this design tool (size, shape, and topology). The students are taught on the algorithmic issues of numerical optimization and work out projects on semi real structural models belonging to different engineering fields. They are also informed on real cases of structural optimization carried out by the faculty of A Coruna University. It has been observed that after completing the course students have their mind ready to apply optimization methodologies to any engineering problem they are confronted with.

Teaching structural design in AEC curriculum is generally distinct from teaching other AEC courses. This is due to the fact that the course typically trains students to think in ways that are not common to other disciplines. Structural design requires knowledge of engineering sciences, art, heuristics rules, and visualization of systems that does not exist yet. These characteristics partially delineate structural design education from other courses. Thus, effective way of teaching structural design in AEC curriculums is often a challenge. This paper centers on the experiences gained in introducing Building Information Modeling (BIM) as a framework for teaching structural design. It explores the role of BIM in structural design curriculum and proposes a new framework for teaching structural design. Utilizing BIM as a framework for teaching structures, BIM tools were investigated as the primary teaching apparatus for advancing other types of structural knowledge that aims at engaging student’s creativity and imagination. At the same time, the framework emphasizes structural correctness, conceptual and quantitative engineering sciences of the structural design. The paper discusses the role of BIM in combining various threads of knowledge such as understanding of space and human activities, forms, circulations, engineering sciences, and the construction process to arrive at structural aesthetic and correctness. The proposed BIM framework will allow engineering students to applaud the union of art and scientific laws, encourage collaborative thinking as a central activity and cultivate professional qualities to meet the demands of future cross-disciplines practice requirements.

Topology optimization has long been touted as a powerful, free-form design tool, capable of generating highly efficient structural solutions. Material may be placed or removed from any point in the design domain, meaning structural connectivity, and therefore structural form, may evolve in the design process. As topology optimization begins to gain traction in the structural engineering design and commercial software industries, this paper explores the potential role of topology optimization as a teaching tool in structural engineering education. In particular, we describe recent efforts at Johns Hopkins University to incorporate topology optimization into all levels of undergraduate education, from freshman-level core courses to senior-level technical electives. These courses thus far include: Freshman Experiences (core freshman level), Perspectives on the Evolution of Structures (core freshman level), 3D Printing and Topology Optimization: Rethinking Engineering Design and Fabrication (freshman elective), Solid Mechanics and Theory or Structures (core sophomore level), and Structural Design II (core junior level). Although typically employed as a design tool, topology optimization is also used in these courses to visualize and improve the understanding of force flow in structures and bodies. We will also describe how these efforts are integrated into the courses Advanced Structural Analysis and Applied Structural Optimization (junior/senior technical electives), transforming the students from users of the topology optimization software (freshman and sophomore years) to developers (junior and senior years). Anecdotal and quantitative assessment of student interest and impact on concept understanding will also be discussed.

New formulas are derived for dynamic analysis of tall slender buildings with large aspect ratio (slenderness ratio) coupled with tuned-liquid sloshing dampers under strong across-wind vortex-induced vibration in consideration of motion-induced aerodynamic damping and stiffness. A tuned-liquid sloshing damper installed at the top of a building is modeled as an equivalent linear mechanical device coupled with building structure; the frequency-dependent aerodynamic damping and stiffness are represented as constant coefficient matrices for the time-domain analysis. Tall slender buildings with aspect ratios exceeding 10 and building heights close to 300m are analyzed to verify the method. Across-wind base moments based on the code and wind tunnel measurement are used in the examples. The effects of the aerodynamic damping and tuned-liquid sloshing dampers are also discussed in the examples.

Non-uniformity of wind loading creates torsional loads on buildings. The torsional loads can significantly modify the distribution of wind-induced forces and need to be addressed in design. This paper presents results of a large-scale experimental study conducted at the Wall of Wind facility of the Florida International University. Torsional loads on a low-rise building were investigated under different opening configurations, and global forces estimated by using pressure taps and load cell measurements were compared. The results showed that the highest global shear forces in the x- direction (normal to the building’s long side) and the highest torsional loads are produced by cornering winds, and that more than 80% of the maximum shear force in that direction and the highest torsional load can occur simultaneously. The shear force in the y-direction was more sensitive to pressure-tap density than the shear force in the x-direction. Single and multiple openings in the building were observed to have minimal effects on wind-induced torsional load for most wind directions.

Present paper describes the details of the experimental study carried out on the models of tall buildings with varying cross-sectional shapes under both stand-alone condition as well as interference condition. Two cross-sectional shapes namely square and triangular are considered. Both force and pressure measurements are made on the models. Rigid models of tall buildings are made of timber for force measurement and of Perspex sheet for pressure measurement. The models are tested in an open circuit boundary layer wind tunnel. Twisting moment developed due to wind is measured in addition to base shear and base moment in along-wind direction as well as across-wind direction. Effect of wind incidence angle on wind loads is studied in case of isolated condition. In case of interference condition, effect of distance between object building and interfering building on wind loads is studied.

The objective of this paper is to develop guidance for design of loose laid roof pavers against wind uplift. Large-scale experiments were performed on concrete roof pavers installed on the flat roof of a low-rise building using the Wall of Wind (WOW) facility at Florida International University (FIU). Both wind blow-off tests and pressure measurements on the top and bottom surfaces of the pavers were performed. The results are used to develop specific guidelines for design of loose-laid roof pavers. Account is taken of pressure equalization, the gaps between the pavers, and the space beneath the pavers. These guidelines are intended to be simple enough to be used by designers in parallel with the usual code provisions for exterior suctions on roofs.

External and internal pressures on a model building with various porosities and dominant openings were obtained in a simulated tornado at a scale of ~ 1:100. Numerical simulations of internal pressures were obtained driven by external pressures collected in the tornado simulator. Comparisons are made between measured and simulated internal pressures. The significant role of porosity and dominant openings in tornado-like flows is discussed.

Laboratory simulations of tornado-like vortices have the advantage of controlled conditions and repeatability. Previously these experiments have been conducted in Tornado Vortex Chambers (TVC). These TVC’s had the advantage of independently controlling the radial/axial flow rate and the tangential components using a fan at the top and a swirling device at the bottom. Because of the swirling device, the flow region of interest is optically inaccessible. The Wind Engineering, Energy and Environment (WindEEE) Dome at Western is a unique large, 3D wind testing chamber, of 25 meters inner diameter and 40 meters outer diameter (including the return circuit). By using a system of 100 dynamic fans on the peripheral walls coupled with 6 larger fans at the ceiling level, WindEEE can produce any type of wind systems including 4 meters in diameter translating tornadoes and downbursts as well as a variety of dynamically shear flows. Flow visualizations and surface pressure measurements demonstrate the variation of the tornado flow field with Swirl ratio which compares very well with the former TVC well controlled experiments. Full scale Doppler radar data and WindEEE PIV measurements are shown to match for a range of Fujita Scales (Fig. 1). Based on this matching, scaling relations between the laboratory (WindEEE Dome) tornadoes and real tornadoes are for the first time drawn.

Post-storm damage investigations of the EF4 tornado which struck Mayflower, AR in April 2014 is reported and utilized to study the influence of hilly terrain on the tornado’s behavior. Preliminary investigations revealed that the damage in the hilly areas is from EF0 to EF3 and in flat areas the damage is rated to be EF2 to EF4. Furthermore, local investigation shows that disruption of the tornadic flow near ground level by the hilly terrain leads to reduction of structural damage. From the observed damage, it is postulated that the hilly regions can effectively produce a sheltering effect, reducing the damage to structures within a region on the leeward side. It is also shown that the tornado’s path is diverted by the presence of hills, which the tornado attempts to travel around rather than over

Thunderstorm downbursts are transient, small-scale events which are, however, the cause of design wind speeds in many parts of the world. The difficulties in predicting when and where such events will occur make capturing full-scale wind loading data for buildings particularly difficult, and so attention has turned to physically simulating downburst flow fields in the laboratory. The University of Birmingham Transient Wind Simulator (UoB-TWS), a 1 m diameter, pulsed impinging jet facility, has been used to physically simulate a downburst and measure the wind-loading on building models which occurs. For the first time, pressure data have been recorded over both single and multiple building model arrangements, allowing interference effects to be quantified. It is demonstrated that the presence of another building nearby can increase drag coefficients by almost 40%, depending on the separation of the building models and the angle of the wind relative to the models.

Wind loads on different layers of a multi-layer wall assembly were determined under realistic loading conditions in the IBHS test chamber. The current results indicated the PEF of 0.36 currently used in the ASTM D3679-13 for vinyl siding is likely too low and a more suitable PEF would be in the range of 0.4 to 0.7, with an optimal value likely between 0.55 and 0.6.. In contrast, the results from the present study on foam backed vinyl siding indicated that the PEF in ASTM D7445-09 of 0.7 are too high and may be overly conservative. The current results indicate most PEF values for foam backed vinyl fall between 0.2 and 0.55.

This paper is focused on assessing the influence of various aleatoric and epistemic uncertainties in the evaluation of seismic performance behavior of wood-frame shear walls using methods of FEMA P-695 Quantification of Building Seismic Performance Factors. These evaluations are completed on the original FEMA P-695 archetype design space consisting of wood-frame shear wall structures designed in accordance with SDPWS – 2008 Special Design Provisions for Wind and Seismic and ASCE 7-05 Minimum Design Loads for Buildings and Other Structures. These results provide additional information on outcomes of the FEMA P-695 methodology for evaluation of wood frame shear wall structures than provided in the original wood-frame shear wall example of FEMA P-695.

The 2015 Edition of the National Design Specification ® (NDS®) for Wood Construction was recently published. The updated standard designated ANSI/AWC NDS-2015 was approved as an ANSI American National Standard on September 30, 2014 (Figure 1). The 2015 NDS was developed by the American Wood Council’s (AWC) Wood Design Standards Committee and is referenced in the 2015 International Building Code (IBC). This paper will discuss the significant changes from the 2012 NDS to the 2015 NDS most of which include provisions for Cross Laminated Timber.

Advances in mass timber construction technology, and the success of recent mid-rise timber structures, indicate the potential for large-scale structures in wood. Several high-rise timber-based hybrid systems ranging from 30 to 42 stories have been proposed but have yet to be realized, in part due to lack of design guidance and concerns about seismic performance, fire, and overall feasibility. This investigation examines three proposed structures: the “FFTT” system from MGB Architects, the “Concrete Jointed Timber Frame” from Skidmore Owings Merrill, and the “LifeCycle Tower” from CREE GmbH. Each is evaluated using Linear Static Analysis for static gravity loads and the loads from the additional mass of Multiple Tuned Liquid Column Dampers, intended to provide not only seismic damping but on-site fire sprinkler supply as well. A comparison of the outcomes provides a basis for future differentiation between the proposed systems including the sizing of members and connections and estimation of initial construction costs.

This paper presents the preliminary design of a rocking Cross-laminated Timber (CLT) wall using a displacement-based design procedure. The CLT wall was designed to meet three performance expectations: immediate occupancy (IO), life safety (LS), and collapse prevention (CP). Each performance expectation is defined in terms of an inter-story drift limit with a predefined non-exceedance probability at a given hazard level. U-shape flexural plates were used to connect the vertical joint between the CLT panels to obtain a ductile behavior and adequate energy dissipation during seismic motion. A design method for ensuring self-centering mechanism is also presented.

This paper presents the seismic design and analysis of a 20-storey demonstration wood building, which was conducted as a part of the NEWBuildS tall wood building design project. A hybrid lateral load resisting system was chosen for the building. The system consisted of shear walls and a shear core, both made of structural composite lumber, connected with dowel-type connections and heavy-duty HSK (wood-steel-composite) system. The core and the shear walls were linked with horizontal steel beams at each floor. The wood-based panel-to-panel interface was designed to be the main energy dissipating mechanism of the system. A detailed finite element model of this building was developed and non-linear time history analyses were performed using 10 earthquake motions. The results showed that the seismic response of the 20-storey demonstration building met the various design criteria and the design details are appropriate.

This paper reports on the potential of timber for structural applications in the international construction market, particularly in the light of its environmental credentials and the advances being made in engineered timber products. The UK market is examined with a specific emphasis on the residential sector, given the target of the UK Government to deliver three million new energy-efficient zero carbon and sustainably built homes by 2020, with a 33% reduction in combined initial and whole life cost of the constructed asset. The paper also reports on the work being undertaken to remove the barriers to timber specification for such applications, through the provision of structural design and detailing tools. These new tools allow a mass customised approach to be taken, facilitate research into practice and improve design efficiency through simplification.