Structures Congress 2017: Buildings and Special Structures

This paper presents nonlinear time domain analysis and its iterative formula for a tuned-liquid sloshing damper installed on a tall slender building under strong vortex shedding excitation. A new iterative formula is derived for a nonlinear time domain analysis of a tuned liquid sloshing damper represented in the mathematical model introduced by Warnitchai, P. in 1998. For the accurate modeling of liquid (typically water) sloshing motion, the nonlinear quadratic damping force which is generated by the liquid flow through a screen is directly implemented without linearizing the term applied in previous studies. Multi-sloshing modes of the liquid are also considered for more accurate modeling. The nonlinear sloshing damper model has been analyzed coupled with tall buildings with heights of 300m and slenderness ratios exceeding 10. The effects of nonlinearity and multiple sloshing mode effects of the liquid and efficiency of the sloshing dampers for different building frequencies and surrounding conditions are investigated. Examples include: (i) time and frequency domain analysis of; (ii) linear and nonlinear; (iii) single- and multi- sloshing mode liquid dampers; (iv) coupled with tall slender building with a range of building frequencies; and (v) under strong vortex shedding and generated from a target wind load spectra based on a Japanese Building Code (AIJ). The present formula can be used to analyze and design liquid sloshing dampers without physical damper test.

Current practice in determining wind loads on a structure is based on the recommendations in the American Society of Civil Engineers Standard 7 (American Society of Civil Engineers (ASCE) 2010), Minimum Design Loads for Buildings and Other Structures. An exposure category is typically selected to represent the surface roughness surrounding a site, this from four discrete exposure categories that approximate all surface roughness conditions. The quantification of these exposure categories are primarily based on research work that was completed in the early 1960s. This paper includes a review of surface roughness and why it is important to wind design, and a review of how findings from current research utilizing geographic information systems (GIS) mapping can address exposure from multiple directions. As an alternative approach to the traditional exposure categories, GIS mapping data that contains surface roughness information for the United States can be used to calculate surface roughness surrounding a site. The data is available from the United States Geological Survey (USGS) and from many local governments. The paper presents a GIS-based approach to determining surface roughness using data directly, without the intermediate step of estimating exposure from the traditional categories.

It is common practice for wind engineers to develop design load predictions based on wind loads that have been determined from a deterministic set of building properties, wind tunnel results and description of wind climate. This many-to-one relationship (many inputs, one load) has thus far served the wind engineering community well as it reduces a complicated problem into a simple account of loads and effects. A stochastic approach considers uncertainty in the design inputs, such as natural frequencies and damping ratio. While this type of approach has been described previously in the literature, the current approach provides a framework in which wind loads can be predicted in practical design scenarios. The current study focuses on tall, slender buildings in an effort to better understand the impact that uncertainties in extreme wind climate, damping ratio and natural frequency have on predicted wind loads, and how these uncertainties contribute to the overall reliability of the structure. A method is described that allows for the direct calculation of probability of failure based on a stochastic relationship between load and resistance.

A new deconstructable composite floor system consisting of precast concrete planks and deconstructable clamping connections is proposed to promote sustainable design of composite flooring systems in steel buildings through reuse of the structural components. This paper presents an experimental testing program to demonstrate the strength and ductility of the deconstructable connectors and the behavior of the structural floor framing system.

Composite action is the joint behavior of two elements connected or bonded together. It is a phenomenon that is utilized in several applications throughout engineering. Previous studies have shown that cold formed steel (CFS) sheathed with structural wood panels exhibits a degree of partial composite action behavior. However currently in the design process, CFS and wood sheathing systems are considered separately in a non-composite manner due to the absence of sufficient supporting data. These systems can include the floors, roofs, and walls of a building. In order to determine the level of composite action present, the slip modulus is needed. The slip modulus describes the relationship between the shear force and the displacement exhibited by two elements in a composite system. The scope of this research is to determine the influence of fastener spacing on the slip modulus and provide a foundation of information to fully define the composite action between CFS and wood sheathing.

Buckling-restrained braces (BRBs) are an important addition to the structural engineer’s seismic design toolkit and are in widespread use in high seismic regions throughout the United States. Recently, designers and researchers have begun considering alternative bracing configurations to capture the benefits provided by BRBs in a fundamentally different way. The buckling-restrained braced mast (BRBM) frame is one such alternative configuration. The BRBM frame consists of yielding BRBs in series with a stiff elastic wide-flange mast frame that is able to pivot about its base. This mast redistributes brace forces between stories, fundamentally changing the kinematics of the system, producing a more uniform distribution of interstory drift, and eliminating the possibility of inelastic weak-story mechanisms. The BRBM system inherently provides for increased redundancy, reducing the number of frames required and providing enhanced seismic performance and better architectural compatibility at a lower cost than conventional brace-frame systems.

The ability to accurately predict engineering demand parameters necessary for estimation of building losses is essential for development and implementation of resilient-based seismic design. Currently available macroscopic nonlinear modeling approaches for reinforced concrete (RC) structural walls can be classified into two groups: (1) models that capture interaction between axial/flexural and shear behavior and (2) modeling approaches with uncoupled shear and flexural responses. Uncoupled modeling approaches are widely implemented in computer programs for structural analysis and showed to be effective tools for simulation of flexural behavior of RC walls. However, their inability to account for shear-flexural interaction could result in underestimation of axial compressive strains in wall boundaries and overestimation of the wall lateral load capacity. This study investigates the impact of the modeling approaches and assumptions used for simulation of seismic behavior of RC walls on estimation of seismic repair losses considering a five-story building designed to current code provisions for a site in downtown Los Angeles under three seismic hazard levels. Presented results suggest that the impact of using coupled versus uncoupled modeling approaches for structural walls is significant for interstory drift estimations at the first building level, slight at the upper levels, and moderate for peak floor acceleration estimations. These differences in the structural responses have marginal impact on the total estimated repair losses for frequent and rare earthquakes, where coupled wall model predicted highest structural losses and smallest nonstructural losses. However, for very rare earthquake events, there is a notable difference between the three models where predicted median repair losses using coupled wall model are 20% to 35% larger than the ones predicted using uncoupled models.

The behavior of thin steel plates under shear loading is governed by early diagonal buckling and subsequent formation of an inclined tension field. This behavior describes the load carrying mechanism in deep steel plate girder webs and steel plate shear walls. Traditionally, steel stiffeners are used on the thin plate in some applications to mitigate out-of-plane buckling and encourage shear yielding, which is preferable and a more stable and energy-dissipating load carrying mechanism. However, the cost and practical difficulties associated with welding these stiffeners, especially on very thin plates and for in-service rehabilitation purposes, are considered as major drawbacks. In this paper, the behavior of thin steel plates strengthened with FRP strips was numerically investigated. FRP wraps were hypothesized to act as an elastic support for the thin steel plate in the early loading stages and as an auxiliary load transfer path in the inelastic tension field action. Numerical investigations were carried out using the finite element method and were divided into two phases; buckling and post-buckling. Elastic eigenvalue analysis for buckling and full inelastic analysis with geometrical and material nonlinearity for the post-buckling phase were carried out. FRP fracture and damage were incorporated in the models. Optimum angle of FRP fibers was studied both for buckling mitigation and post-buckling behavior enhancement. A number of FRP strengthening configurations together with a range of common FRP materials were also employed in the analyses. It was concluded that bonding FRP patches on the steel plate can effectively encourage behavior enhancements, especially given appropriate configuration and material properties.

Typical Peruvian schools were built with a now out-of-date seismic code that does not guarantee the student population safety. This type of buildings presents an undesirable structural failure known as short column, i.e. slender columns partially restrained by infill walls. The objective of this paper is to evaluate a low cost retrofitting techniques proposed by a previous study in accordance to the incremental retrofitting methodology proposed by FEMA 395. Incremental dynamic analysis, IDA is used to analyze original and retrofitted structure in terms of structural response and damage state for different intensity levels. The results of these analyses reveal the effectiveness of the interventions in terms of economic values.

This paper addresses technical issues related to structural wind design of tall buildings and their effects on performance-based design (PBD). The issues include (i) across-wind loading due to vortex-shedding which is one of the governing design parameters for tall buildings, (ii) along-wind loading due to wind-buffeting and its probabilistic distribution for tall building design, and (iii) the comparison of wind design versus seismic design on PBD basis. The intended use of this study is to discuss about the cost-saving effect and feasibility of PBD compared to the conventional tall buildings’ wind design by quantifying those effects based on an example of a typical tall building. The efficiency of wind design based on a PBD approach similar to that which has been applied to earthquake engineering is applied to the example of a tall building and the cost-saving effect of PBD is discussed based on the results. In order to derive generalized results, the study is performed for a generic tall building with a square plan of 30 m by 30 m, and a building height of 300 m, with a resulting aspect ratio (slenderness ratio) of ten (10). Dynamic structural properties of the building including building frequency, mass density and mode shapes are assumed based on the authors’ experience with typical tall buildings. The across-wind and along-wind responses of the tall building are simulated for a range of return periods to discuss about the implication of performance-based wind design of tall buildings. The paper will provide insightful and practical information that structural engineers can use for their preliminary or detailed structural wind design of tall buildings.

The ASCE 41 Committee is currently completing the balloting of revised steel column modeling and acceptance criteria which will be included in the 2017 edition of the standard. The revised column criteria are a significant update to the current ASCE 41-13 provisions, and are based on research performed by Popov (1975), MacRae (1989), Brownlee (1994), Newell-Uang (2008), Uang-Ozkula (2015), Suzuki-Lignos (2015), Elkady-Lignos (2015) and limitations highlighted by Bech et al (2015) with the current criteria. The updated steel column modeling and acceptance criteria are based on a series of regression analyses performed on 220 different column hysteresis collected from the various researchers outlined above. The regression analyses were performed to fit the “a”, “b” and “c” parameters as defined by section 7.6 of the ASCE 41 standard. The completed equations and justification for the input parameters are presented along with the statistical measures taken from the regression. For seismically compact sections with low to moderately-high axial loads, the parameters and equations correspond with ductile, deformation-controlled behavior, rather than force-controlled behavior per ASCE 41-13. In general, the revised criteria result in less conservative predictions of column performance relative to ASCE 41-13. It is thus anticipated that the revised ASCE 41-17 provisions will result in less costly and intrusive retrofit solutions, and better characterizations of performance, than were developed under prior editions of the standard.

Non linear time history seismic analysis is notoriously time consuming and can be very tedious to set up and execute. A systematic and automated approach is critical in ensuring that these highly complex models are generated accurately and stay in sync with the documentation model. This paper will illustrate a highly automated and scalable approach in managing the workflow from model generation, analysis, result storage and post processing. It will describe the compression in time scale required for such analysis and its beneficial impact on structural design. This paper will conclude by speculating on the impact of such workflow compression on enabling robust seismic design while supporting architectural expression and/or heightened seismic performance targets.

Lateral loads primarily induce axial loads in members of steel concentrically braced frames but columns may also be subjected to drift induced bending moments that may affect their strength and stability. The article discusses three examples of CBF columns that are subjected to combined axial compression and bending moments in structures under severe seismic ground motions: columns at an intermediate level where soft-story response develops in an existing seismically deficient X-bracing, fixed base columns at the first level of a well-proportioned multi-story X-bracing system, and columns in multi-tiered braced steel frames. Nonlinear dynamic analysis of the columns is performed to examine their stability response under axial and bending demands. In the first two cases, the results indicate that bending moments have limited effects on the global stability of the columns. Conversely, columns in multi-tiered frames must be designed to resist the expected combined axial and flexural demands in order to prevent column instability.

Wide-flange sections are routinely used for the construction of seismic force-resisting systems in the U.S. For braced frames, shallow, stocky sections are commonly used. However, deep sections are used nowadays in order to achieve economy when designing moment frames. Recent cyclic testing of deep, slender steel columns under varying degrees of axial compression showed that the failure mode can be very different between shallow and deep sections. Since the hysteretic response of a column is associated with the governing failure mode, for analytical modelling purposes it is essential that a straightforward criterion be established to identify the governing buckling mode. This paper proposes one criterion based on the full-scale test results. The proposed criterion is also verified by finite element simulation of wide-flange columns with a wide range of geometric properties.

This paper investigates the structural behaviour of an innovative beam-to-column composite semi-rigid joint with deconstructable post-installed friction-grip bolted shear connectors and Grade S690 high strength steel flush end plates. Non-linear continuum-based finite element models are developed and validated against the results of four full-scale laboratory tests of this innovative joint. The validated finite element models are used for conducting an extensive parametric study in which the effects of the reinforcement ratio, thickness of the precast concrete slab, degree of shear connection, size of the bolts in the connection zone and thickness of the flush end plate on the structural behaviour of a composite joint with deconstructable post-installed friction-grip bolted shear connectors and Grade S690 high strength steel flush end plates are investigated.

In this paper, we present a new methodology for achieving minimum-cost retrofitting design solutions. Nonlinear fluid viscous dampers and their supporting braces are optimally distributed in irregular 3-D frames and optimally sized. For generating optimal design solutions useful for practitioners, a realistic cost formulation is chosen as the objective function to be minimized. Constraints are imposed on inter-story drifts at the peripheries. These are evaluated with nonlinear time-history analyses considering realistic ground acceleration records. The behavior of each damper-brace system is defined based on the Maxwell’s model for viscoelasticity. A fractional power-law is used to describe the nonlinear force-velocity relation of each damper. The stiffening contribution of the supporting brace and of the damper is represented by linear springs. The damper-brace elements are divided into size-groups, that is, elements with the same mechanical properties. The properties of each size-group of dampers (damping coefficient and supporting brace stiffness), and the dampers’ distribution in the structure are optimally defined. The optimization problem is first posed and solved as a mixed-integer problem. To reduce the computational effort required in the optimization, the problem is then re-formulated with continuous variables only and solved with a gradient-based algorithm. Material interpolation techniques play a key role in achieving practical final design solutions with a reasonable computational effort. Promising results attained for a 3-D irregular frame are presented and discussed.

As topology optimization is a free-form approach to optimizing structural layout, it has a tendency to design structures that are topologically complex. In large-scale structures, this complexity drives construction costs significantly higher, potentially overtaking cost savings from reduced material usage. This work examines opportunities to incorporate complexity measures directly into the topology optimization of structures such that the designer gains control and may explore potential constructability-performance tradeoffs. In particular, the cost of topological and connection complexity is considered. The algorithm is formulated in a continuous form such that sensitivities are readily available for use with rapid gradient-based optimizers. The algorithm is demonstrated on static design problems and solutions. The tradeoffs between constructability, material usage, and performance are explored.

This paper presents an investigation into the use of cast steel replaceable links for eccentrically braced frames (EBFs). While conventional EBFs can be designed with a large response modification factor, and are thus very economical seismic-force-resisting systems (SFRS) in high-seismic regions, they can also be prone to damage states such as fracture at stiffener welds, local buckling, and lateral torsional buckling. They are also difficult to repair after an earthquake event since the EBF links are integrated into the floor beam of the seismic force-resisting frame. It is proposed that these drawbacks of conventional EBFs could be mitigated by using replaceable cast steel yielding links, since demand critical welds are avoided and damaged links can be replaced after an earthquake. Additionally, the cast steel EBF links are uncoupled from the beam sections and thus the most economical beam and link can both be specified. This paper presents sample building designs for a variety of building locations, using a newly developed cast steel EBF link concept that can be used to achieve more economical designs while also improving the performance of EBF frames.

Post-tensioned (PT) flat-plate gravity framing systems are highly efficient and reduce embodied carbon when compared to conventional reinforced concrete framing systems. Efficiency is especially apparent in multi-span applications with regular orthogonal support arrangements. Even though PT flat-plate gravity framing systems are less efficient in single-span or irregular support applications, they are is still useful in reducing slab thickness, improving construction efficiency, and reducing seismic mass. A novel approach to determining PT tendon arrangements has been applied to several buildings informed by topology optimization results. Topology optimization is an optimization method which determines optimal load paths in a finite element continuum. Thus, by orienting PT tendons along the optimal load paths suggested by topology optimization, it has been shown that 25% or more of PT quantities can be reduced while maintaining the same mild steel reinforcement. Many of the observed arrangements do not follow traditional uniform/banded arrangements. Also, the deflection performance is significantly more consistent since tendons are resisting load in a manner consistent with the load demands. This can help alleviate common issues with thin flat-plate gravity systems such as irregular floor flatness due to warping incited by PT systems and inconsistent deflection at the exterior wall. This new design method has been applied to three buildings and coordinated with construction teams for efficient application. This presentation will discuss the entire design procedure from initial concepts through complete construction documents as applied to three buildings. This presentation will be of interest to academics and practicing structural engineers.

An innovative, lightweight, rapidly constructible and reconfigurable modular steel floor (RCRMSF) system has been developed. To understand the strength and serviceability behavior of the system, a performance based design methodology has been formulated and a finite element analysis (FEA) parametric study carried out. This design methodology is based on limit states including plate yielding, connector failure, service load deflections, and vibrations. Additionally, through Abaqus FEA software, the load and vibration response of the system is studied. The study is further expanded to investigate the effects of varying parameters, including plate thickness, channel thickness, channel spacing, and floor depth on the load response and vibrational characteristics of the system. The floor system has shown adequate strength and vibrational characteristics, for office use, considering a RCRMSF fabricated from 2.45 mm thick light gauge steel plates, 254 mm deep x 1.72 mm thick channels at 610 mm spacing, and based on a 12.2 m x 9.1 m bay size.

A rope net sculpture was developed for the Sunset La Cienega project in West Hollywood, CA. The sculpture was designed in collaboration with artist Janet Echelman and spans the two towers of the development. The sculpture is articulated into four levels of structural net layers and several sculptural nets made of fishing net-type material hanging from the structural layers. The structural design of the sculpture presented several challenges from the analytical and material points of view. The design process required form finding of the structural rope net layers followed by dimensioning of the rope elements. Rope structure materials are highly non-linear due to their construction and are relatively soft compared to traditional structural materials. This paper describes these challenges and the most important aspects in the design of the rope net sculpture.

Tubular steel monopoles (poles) are popular support structures in many industries today and have been utilized as support structures in the communications, sports lighting, electric utility, and transportation industries for many decades. The number of poles in the communications industry has exploded in recent years caused by the ever-increasing demand for voice and data usage on wireless devices. Poles have a proven history of being reliable support structures, however, in the last decade there have been numerous failures of steel poles across the country in various industries that can be attributed to unmitigated cracks in welds (“toe cracks”) at the pole to base plate connection. The property damage, in some cases, has been significant; and at the very least there are service interruption and repair/replacement costs associated with the subsequent loss of the structure. There are many contributing factors to this toe crack issue. Field inspections have shown the importance of understanding and reacting appropriately regarding this issue. Visual and NDE inspection techniques are critical and should be regularly scheduled. It is imperative that inspections are carried out by qualified personnel with specific pole experience, CWI credentials, and non-destructive ASNT credentials. If identified via timely inspection, these defects can be resolved via engineered weld repairs which restore the original integrity of the structure. Timetable for the required repairs is based on the severity of the weld cracking and age of the structure. As with America’s other aging infrastructure, the cost of ignoring this issue can be significant to public safety and welfare. This paper presents a proposed monopole base crack classification system which is intended to standardize the way the industry deals with inspection, repair, and maintenance of pole base connections.

An eddy current damper (ECD) offers effective vibration suppression by dissipating energy through circular currents produced inside a conductor that is subjected to a varying magnetic field, running through the resistivity of the conductor. Due to its non-contact and fluid-free characteristics, an ECD does not add significant mass and stiffness to the structural system, and eliminates maintenance needs for tuning, leakage, etc. Unlike other viscous dampers used in building structures, an ECD works by producing a damping force that is a linear function of velocity. ECDs have been widely researched and used for various mechanical applications, but their implementation in building structures has been limited. The literature on the use of ECDs in structures has mainly focused on theoretical models and model validations to describe the damping mechanism; relatively little is known about the design practice involving ECDs. Utilizing finite element analysis, this study identifies key design parameters and the design process involving an ECD, based on electromagnetic theory and validated analytical models. The goal is enable design engineers to select and implement passive ECDs in building structures.

Fireproofing is a passive fire protection applied structural steel members to reduce heat transfer to the structural steel members so that the rate of temperature rise of the load bearing components is reduced and a structural failure is delayed or does not occur. In other words, fireproofing helps the structural elements to properly function during a fire event for a certain period of time, also know as fire resistant rating. Different types of fireproofing applied to structural steel members such as concrete encasement, spray applied fire resistive materials (SFRM), intumescent coating, and gypsum board. This study focuses on the concrete encasement, which is widely used in oil and gas refineries and petrochemical facilities. Damage to fireproofing may occur due to accidental damage, long-term weathering, vibration, and improper application during construction. It is very important to understand how effective damaged fireproofing is since it is a phenomenon that occurs more often in practice. Damaged fireproofing or loss of fireproofing affects the strength and stiffness of structural steel members dramatically and raises the question of how effective is the remaining fireproofing during a fire event. Different types of damage such as extent of damaged fireproofing along the length of the members, partial loss of fireproofing across its thickness, and location of the damage. Failure modes, deflection, member capacity, and local instabilities were investigated at elevated temperature and compared with same members that are fully protected and without damage.

The compressive strength of masonry is an important consideration in the design of masonry structures and is principally determined using one of two methods specified in The Masonry Society, TMS 602-13 “Specification for Masonry Structures” the prism test method (PTM) and the unit strength method (USM). The USM is inherently conservative and should be used in combination with fully bedded masonry. However, what if face shell bedding were used, what is this compressive strength and would the USM still produce conservative estimates? A means to attain f’_m for face shell bedded masonry using the USM would be to utilize a strength ratio between full and face shell bedding types. TMS 602-11 specified a strength ratio, however, this was removed beginning with the 2013 edition. This is problematic because the USM does not specify the use of fully bedded joints, thus, creating a potential interpretation that it is permissible to utilize face shell bedding and that it would achieve the USM f’_m compressive strength estimate. This interpretation though would be erroneous and un-conservative. Hence, there is a need to flush out, clarify and substantiate f’_m for face shell bedded masonry; further, to validate the USM compression strength estimates of fully bedded masonry. A total of 48 compression tests of various prism configurations for both face shell (24) and fully bedded (24) prisms were conducted; from the results, a new data base was generated to substantiate f’_m for face shell bedded masonry as well as recommendations for amending the TMS 602 for the upcoming code cycle.

Previous studies by the authors discussed the behavior of unstiffened and stiffened extended shear tab connections, highlighted the differences between both types and discussed the applicability of stabilizer plate requirements to skewed extended shear tab connection. This study presents a parametric study and proposes a design procedure for skewed extended shear tab connections based on results obtained from finite element analysis for 300 models with different configurations using the finite element software ABAQUS. The variable parameters used for this study are: plate thickness, the distance between the weld line and the bolt line, skewed angle, and number of bolts. These parameters were investigated in terms of the connection vertical displacement, plate twist along the bolt line, plate twist along the weld line, and the connection shear capacity. Modifications to the current connection lateral stability checks in the literature will also be addressed. The proposed design procedure on this study is specific procedure for the skewed extended shear tab connections. This procedure is compared with the current design procedure in the AISC Manual 14th edition.

The restoration of the dome of the United States Capitol Building was a project that required years of careful planning prior to entering the bid process. One of the major components of the project involved determining how to safely access the work surfaces to allow for the restoration work, which involved cast iron crack repair, lead paint abatement, and temporary removal of much of the ornamentation. Additionally, since any construction access structure would remain on the building for an extended period of time, the appearance of the dome during the work was an item of concern as well. This paper serves to discuss the process of designing, value engineering and finally constructing the exterior scaffolding around the dome of the Capitol building.

Phase 1 of the Second Avenue Subway in Manhattan, New York, is nearing completion. There are two mined cavern stations and one cut-and-cover station in this phase. All three stations have reinforced concrete mezzanines of similar geometry, with a large single span beam and slab system. This configuration allows for the provision of unobstructed column-free spaces at platform level and large central penetrations for vertical transportation. Each mezzanine is integral with the varied station shell types, providing intermediate lateral support, but each mezzanine was built under separate construction contracts. These factors required complex modelling of each system. The contrasting behavior of each station shell type and their respective construction staging results in significant differences in forces applied to the mezzanines, and in detailing, for both station types. Maintaining a consistent architectural feel between all stations required a unique structural design approach. This paper will discuss the design process, construction methodology and construction sequencing for each of the mezzanines, and review the similarities and differences in the design forces and subsequent structural design details for each. Special design considerations for large spans will also be explored. As construction of the mezzanines is now complete, the paper will review the final construction methodologies adopted and how these impacted the design. Attendees will gain an insight into the design of intermediate permanent lateral supporting systems in underground structures with large penetrations, and an understanding of the degree to which construction techniques and construction contract packaging can drive the design and detailing of structural members.

Adobe walls have the inherent mass that significantly contributes to their blast resistance, but lack the energy-absorption capability. Therefore, it is necessary to develop engineering guides for predicting the response of such structures under blast to develop blast-retrofit designs. This paper will focus on the analytical and experimental programs for characterizing the static resistance function of full-scale adobe block walls. The adobe walls tested closely simulate the boundary conditions of a wall that is part of an adobe structure, including side walls and roof system. The experimental results were used to verify the 3D numerical models developed for predicting the resistance function of adobe walls and wallettes. Wallette adobe systems that were tested in four-point bending showed that the failure of an adobe structure is significantly related to the stability of an element. The un-retrofitted vacuum chamber test results were used to design and evaluate various blast retrofit systems.

One of the methods used to design reinforced concrete buildings against lateral forces is the use of moment resisting frames which comprises of beams, columns, and the interconnection of beam-column joint. The weakest link in this type of structure is the beam-column joints (BCJ). The BCJ are important for framing action for gravity loads, lateral loads, and combination of both, though, it is the lateral loads that place the largest demands on BCJ. If BCJ could regain their original shape and strength with a minimum repair after an earthquake, then the problems associated with permanent damage could be mitigated. Of the numerous ways to retrofit or repair a deficient BCJs is the use of carbon fiber reinforced polymer (CFRP) composite. Most of the work done on strengthening with CFRP are by applying the CFRP sheets on the web and around the BCJs for shear strengthening, while little has been done on strengthening of BCJs for flexural-shear failure. Hence this research studies the behavior of BCJs made with concrete of compressive strength in the range of 50-60MPa, without shear reinforcement at the joint. The effectiveness of CFRP in retrofitting such BCJ using externally flange bonded CFRP by relocating the plastic hinge from the interface of the BCJ to a distance inside the beam. It was observed that such BCJ failed in flexure, with plastic hinge formation at the interface of the BCJ, followed by yielding of the beam flexural reinforcement. The retrofitted samples, showed improved ductility, load carrying capacity, with the plastic hinge moved from the interface of the BCJ to the termination point of the CFRP on the beam.

During an investigation into the failure of a helical pier foundation system at a residential building we evaluated of the retrofit brackets that are often used for underpinning existing structures. These brackets are also referred to as side loaded or “L” brackets where the horizontal leg of the “L” is positioned below the footing or foundation wall and the vertical leg is positioned against the vertical face. This arrangement creates a couple due to the offset between the center of load from the foundation wall and the center of bearing on the horizontal leg of the bracket. We refer to this offset as the structure eccentricity. The moment generated by this offset is often resolved by the floor framing or other elements within the superstructure and to be evaluated on a case-by-case basis.

Prefabricated composite wood I-joists are very common in North America as a building materials for light-frame wood construction. The capacity and the failure pattern of prefabricated composite wood I-joists in the presence of a flange notch was experimentally investigated with a total of 6 specimens with various sizes and locations of notches having a span length of 6.1 m (20 feet). Test results showed that the presence of a notch reduced the capacity significantly up to 75% compared to I-joists having no flange notch depending on the size and location of the notch. The web of the control I-joists with no opening failed in flexure in the mid-span whereas the top-flange failed in compression and bottom-flange failed in tension. On the other hand, most of the I-joists with a notch failed in flexure at the notch location. The performance of flange notched I-joists retrofitted with glass fiber reinforced polymer (GFRP) plate was also investigated on another 18 specimens. After retrofit, brittle premature failure of I-joists was prevented with a significant increase in capacity up to 307% compared to the I-joists with notches was achieved. Based on the experimental results, a prediction model was developed and validated with the experimental results.

Many urban areas throughout the world are subjected to cascading failures due to the interdependent nature of infrastructure systems. As complex networks have developed they have magnified existing levels of vulnerability in densely populated areas. These interdependencies must be identified and mitigated against. The Denver regional area is used as an example in this study showing several of the physical and geographical interdependencies. The criticality of these interdependencies is shown in terms of potential stressors prevalent in the Denver region.

Since the introduction of ANSI A58.1-1972, provisions for seismic load analysis have evolved from simple 2-dimensional static analysis to complex 3-dimensional procedures that may require the representation of diaphragms as semi-rigid, incorporate physical mass offsets to account for accidental torsion, directly include P-Delta effects, and include bidirectional loading. The determination of the complexity of the analysis arises from a variety of rules that trigger decisions based on system features that may be determined a priori, or which may necessitate side analyses that are themselves complex. These rules were introduced incrementally over several code cycles, due in part to the increased availability and capacity of computers and analysis software. This “bottom up” approach in which rules are applied to increase analysis complexity is still used in ASCE 7-16. In this paper, an alternate “top down” approach is recommended wherein the basic requirement is to develop a detailed 3-dimensional analytical model, and then use exceptions where appropriate to simplify the analysis. It is believed that this approach may pave the way to more rational analysis in future editions of ASCE 7, with the goal of eliminating modal response spectrum analysis in favor of linear response history analysis, and eventually, to provide a design-based nonlinear response history analysis procedure in Chapter 12.

Reinforced concrete structural walls are common in mid- to high-rise structures in high seismic regions, and are expected to have good strength and ductility characteristics if designed in accordance with ACI 318-14. However, experimental and analytical investigations of reinforced concrete structural walls and isolated boundary element prisms indicate that the existing design provisions may be insufficient to provide ductile, flexure-dominated response under cyclic loading. Walls designed with an ACI compliant boundary element length are susceptible to shear-compression failures below the maximum ACI allowable shear stress of 10A_cv√f_c’. Also of concern is the frequent use of thinner walls in modern design; as the wall’s cross-sectional aspect ratio increases, such brittle shear-compression failures occur at even smaller shear stress values. In regards to detailing, special boundary elements with intermediate cross-ties exhibit a minimal improvement in confinement compared to ordinary boundary elements. This response can be linked to inadequacies in multiple code design parameters, including: vertical spacing and area of confinement steel, horizontal spacing and type of restraint to longitudinal bars, and development length provided for transverse reinforcement. Recent in-field wall failures have prompted concerns related to the minimum code required vertical and horizontal web shear reinforcement, as well as the relative amount of vertical-to-horizontal web steel. This paper examines ACI 318-14 special boundary element and web reinforcement provisions and provides design recommendations intended to improve wall performance as compared with current ACI requirements.

During a seismic event, the fluid-viscous dampers utilize the action of solids to enhance the performance of structures subjected to transient environmental disturbances for general shock and vibration mitigation purposes. The conventional cylindrical viscous dampers contain compressible silicone oil which is engaged to flow during a disturbance through the action of the stainless steel piston rod with a bronze head. Possible compressible oil leakage in damaged damping systems may negatively affect the response of the degraded damping system and, ultimately, the response of the entire structure, during a seismic event. It creates a gap or lapse in the force-displacement response. This paper investigates the seismic response of Beijing Yintai Center for various viscous fluid leakage percentages in damping systems which are mainly manufactured and supplied by Taylor Devices (U.S.) and the Beijing QITAI shock control and scientific development in China. One of the main objectives of this study is to investigate the performance of viscous dampers under different conditions of possible leakage volumes against their basic response characteristics. The damper is able to handle a portion of the assigned displacement time history without developing any reaction force. However, when the displacement of the internal piston reaches a sufficient level to regenerate fluid pressure, the damping force trend is restored through a “delay” whose length depends on the amount of the fluid leakage. The study is based on the time history analysis of selected and scaled earthquake records according to the ASCE 7-10 along with the numerical analysis of simulated damaged/leaking damper devices using finite element and structural analysis software. The analyses results demonstrate the change in performance of the structures with degraded damper devices. The inter-story drifts and base shear values are dramatically increased in structures with degraded damper devices.

Performance-based design (PBD) proves to be a robust approach that can ensure the satisfaction of stakeholder desired target performance objectives during the design of structural systems, especially for areas prone to severe natural hazards. While the application of PBD has been widely applied for achieving earthquake-resisting structural systems, the concept of PBD has only recently been expanded to wind engineering. In particular, the integration of PBD concepts within topology optimization in an attempt to achieve both reliable as well as economically-viable systems within severe wind environments has recently been explored for 2D structural systems. Therefore, the definition of a performance-based topology optimization framework within a fully 3D space would represent a significant bridge between theoretical findings and practical applications. This paper illustrates the development of such design framework. First, a PBD methodology is briefly reviewed. Then, a discussion is presented on how to schematically incorporate the concepts of PBD into the constraint functions of a 3D topology optimization problem through the adoption of an appropriate set of performance-based design constraints. Finally, a case study is presented in order to demonstrate the validity and effectiveness of the proposed 3D PBD topology optimization framework.

This paper examines the effects of foundation uplift on the dynamic response of steel frames supported by shallow foundations. In order to achieve this goal, the dynamic responses of a number of two-dimensional concentrically braced steel frames with fixed base, flexible base preventing uplift, and flexible base allowing uplift, are compared. The steel frames are modeled by considering material nonlinearities and P-Delta effects, while the soil-foundation system is modeled through the Winkler foundation approach. The dynamic analyses are conducted using 15 far-fault ground-motions with various intensities and different response parameters are monitored. According to the achieved responses, the presence of foundation uplift generally increases the total displacement demands and reduces the inter-story drift ratio and ductility demands. The important parameters affecting the responses of uplift-permitted frames are also introduced and examined.

This paper discusses the benefits of performance-based seismic and wind design, including allowing controlled limited yielding under wind loads. For tall buildings in earthquake prone regions, it is often found that the design of certain structural elements (e.g. buckling-restrained brace outriggers) is controlled by wind demands, forcing these elements to be stronger or stiffer than would otherwise be required to meet seismic design objectives. These wind controlled elements can start a chain reaction, wherein the element size is increased for wind demands, which results in a stiffer element and therefore greater seismic demands. The seismic performance and economy are further hindered by the necessary seismic design principles of controlled yielding and capacity design, where increasing the size of energy dissipating elements tends to produce a cascading detrimental effect upon columns, diaphragms, foundations, connections, and other structural elements. In recent years, proposals have been put forward to extend the performance-based framework to wind engineering, with thus far limited implementation due to technical, practical, and jurisdictional challenges. This paper will further express the relevance and state of practice in combined hazard performance-based design.

The use of deep wide flange steel columns is prevalent in seismic zones. However, their inelastic behavior, in general, and collapse capacity, in particular, under combined axial and lateral loading are not yet well understood. In order to address this shortcoming, the effect of drift loading history on the performance of deep columns subjected to various levels of constant axial force with different boundary conditions is investigated. Detailed finite element models that are validated using available experimental data are employed in this study. Three drift loading protocols are used: (1) symmetric cyclic loading, (2) asymmetric cyclic loading, and (3) monotonic loading. The drift loading histories are specifically selected to highlight key differences between idealized and realistic seismic demands as observed from complete frame analyses for collapse-susceptible first-story columns. The simulation results show that selecting a proper loading history is critical for assessing the collapse capacity of deep columns. The failure modes observed from the simulations are dominated by the global out-of-plane slenderness ratio, local slenderness ratio, and boundary conditions. The simulation results are used to assess the suitability of current design criteria.

Full locked coil ropes (FLC) were first produced in the middle of the 19^th century. They are used in all kind of structures that are defined by lightweight aesthetics such as stadium roofs, membrane roofs, pedestrian bridges and glass facades as well as in structures with a more functional focus such as stayed masts, vehicular bridges and pipeline bridges. Despite their wide range of applications and many advantages over other tension members the awareness of structural engineers and architects towards FLCs is still limited. The goal of this paper is to raise the level of familiarity for this unique construction element. The paper will compare the design and the mechanical properties – like weight to load bearing ratio, stiffness, pre-stretching, pre-tensioning and corrosion protection – of a FLC to other types of rope – such as spiral strand rope, stranded rope and bridge rope – and other tensions members – e.g. round steel bars – and present the advantages and disadvantages a FLC has in comparison. The paper will also give an introduction to how a FLC is designed and manufactured according to current standards and to unique demands of different structural applications. The presentation will provide an overview over some landmark structures that were build or are currently being build using FLCs.

The Minnesota Vikings are known for their winning teams, a 1960’s and 1970’s dominating defensive line nicknamed the “Purple People Eaters,” a Pro Football Hall of Fame former head coach, and advancing to four Super Bowls. It was clear to the Minnesota Sports Facility Authority after the December 2010 Minneapolis snow storm that produced a substantial tear in the venerable Metrodome’s air-supported, Teflon coated fiberglass roof structure, allowing snow to fall inside the building, that a new stadium was necessary for the Minnesota fans. Soon after, the Minnesota Sports Facility Authority, Vikings owner’s Zygi and Mark Wilf, and Dallas-based architect HKS, began visioning a new amenity-rich, transparent roof multi-purpose stadium. The Metrodome (constructed for $55M in 1982) was demolished in early 2014, paving the way for the new stadium on the same Minneapolis Downtown East site.

Current U.S. codes and standards provide limited guidance on advanced structural fire analysis. The ASCE Fire Protection Committee is developing a performance-based design guideline for fire to provide guidance on analysis techniques and performance criteria for advanced fire analysis methodologies. This paper provides the results of an on-going research project that uses advanced fire analysis techniques to evaluate progressive collapse mechanisms in a ten-story steel-frame office building. This paper presents the results of multiple analyses that vary the fire resistance rating of the structural members subjected to a full-story design fire. The fire protection on each of the structural members (beams, columns, connections) was: (i) design FRR (1hr) on each structural member, and (ii) columns protected with 2hr FRR, beams protected with 1hr FRR. The results of these analyses were compared to the results of previous compartment fire analyses performed by the authors.

This paper presents the numerical modeling of a test on a 6-meter-long steel W-section beam subjected to combined structural load and localized fire. An integrated fire-structure simulation approach was successfully applied to model the fire-thermal-structural behavior of the beam specimen. The difference ratios between the predicted and measured values for failure time, failure temperature and failure load can be as small as 0.7% (0.2 min), 2.9% (19 ^oC) and 9% (9 kN), respectively. In this paper, failure temperature is defined as the maximum temperature in the beam specimen at the onset of failure. Detailed description of the numerical models was presented. The study might serve as a validation case of the integrated fire-structure simulation approach which could be used in structural fire engineering design.

In this paper, we discuss the structural design of one of the tallest timber-based hybrid buildings in the world: the 18 storey, 53 meter tall student residence on the campus of the University of British Columbia in Vancouver. The building is of hybrid construction: 17 storeys of mass wood construction on top of one storey of concrete construction. Two concrete cores containing vertical circulation provide the required lateral resistance. The timber system is comprised of cross-laminated timber panels, which are point supported on glued-laminated timber columns and steel connections between levels. In addition to providing more than 400 beds for students, the building will serve as an academic site to monitor and study its structural performance, specifically horizontal building vibration and vertical shrinkage considerations. We present the challenges relating to the approval process of the building and discuss building code compliance issues.

The Ferdinand Building is located in the Dudley Station Historic District, a district listed on the National Register of Historic Places. The building is located at the intersection of Washington and Warren Streets. The city of Boston proposed to construct a new municipal building on the site. There had been several proposed uses for the building in the past. None of them were successful. The redevelopment of Dudley Square was the passion of the late Mayor, Thomas M. Menino. The proposed building for the site covered the entire block and would be eight stories high. To help blend the new building into the fabric of the neighborhood the City required the walls along Washington and Warren Streets be incorporated into the design of the new building. Working with Shawmut Design and Construction, John Looney designed a bracing system to allow the old building to be removed while maintaining the façades.

Model building codes in the United States limit timber construction to six stories, due to concerns over fire safety and structural performance. With new timber technologies, tall timber buildings are now being planned for construction. The process for building approval for a building constructed above the code height limits with a timber load-bearing structure, is by an alternative engineering means. Engineering solutions are required to be developed to document and prove equivalent performance to a code compliant structure, where approval is based on substantive consultation and documentation. Architects in the US are also pushing the boundaries and requesting load-bearing timber be exposed and not fully encapsulated in fire rated gypsum drywall. This provides an opportunity for the application of recent fire research on exposed timber to be applied, and existing methods of analyzing the impact of fire on engineered timber structures to be developed further. This paper provides an overview of the performance based fire safety engineering required for building approval and also describes the engineering methodologies that can be utilized to address specific exposed load-bearing timber issues; concealed connections for glulam beams; and the methodology to address areas of exposed timber.

This paper provides a brief description of the structural and seismic design of the new Tocumen International Airport south terminal, currently under construction in Panama City, Panama. With a gross area of 860,000 sq ft (80,000 m²), the new terminal has a curvilinear shape 2,164 ft (660 m) long by up to 531 ft (162 m) wide on plan and is classified as an essential facility. Foster + Partners adopted the state-of-the-art performance-based seismic structural design methodology, incorporating nonlinear static pushover and nonlinear response history analysis methods. The roof is one of the primary design features of the new terminal. Framed in structural steel and supported on reinforced concrete columns, it comprises curved plate girders spanning up to 151 ft (46 m) between tubular girders that are faceted on plan and on elevation along the curved perimeter. Beneath the roof the seismic force-resisting systems include reinforced concrete moment frames and shear walls. Following capacity design principles and with innovative reinforcement detailing, the tops of the reinforced concrete roof columns are carefully designed to act as ductile fuses. The fuses limit the maximum seismic demand that can be transferred to the steel roof, which is designed to remain essentially elastic under MCE shaking.

The recently constructed St. Louis County Emergency Communications Center was designed to consider multiple natural and manmade hazards in an effort to provide a facility that would be able to withstand a significant extreme event and still maintain the level of operability required to provide both emergency communications and post disaster response for St. Louis County. St. Louis County recognized that having an emergency response facility that is fully operable after an extreme event is one key aspect to promoting community resilience. The communications center was designed in accordance with the 2009 International Building Code (IBC), as adopted by St. Louis County, supplemented by other relevant design standards. The natural hazards for which the building was designed included elevated seismic loads as well as extreme wind loads. The prescribed manmade hazards reflected the requirement to provide a level of anti-terrorism/force protection (AT/FP) that is commensurate with the function and importance of the facility. This paper will examine both the development of the design criteria and integration of the different conventional and extreme load criteria into a cohesive multi-hazard strategy to provide a higher level of protection for both structural and non-structural elements that were deemed to be critical to the post-event operations of the facility.

In the aftermath of the devastating 2010 Haitian earthquake, the U.S. government freed up some funds to help reconstruct the country’s collapsed infrastructure. The authors were involved in the design of and construction administration for some of this infrastructure, specifically for law-and-order facilities including six police stations and three prison complexes. This paper will cover some of the lessons learned from these endeavors. Special design challenges on these Haitian projects included more than just high seismic and wind loads. The lack of locally available skilled labor and the need to import most construction materials were coupled with a governmental owner’s limited ability to provide consistent construction oversight. Coordination with local professionals, such as geotechnical engineers, was essential, but it proved difficult to receive recommendations essentially in accordance with ASTM or ASCE standards. As such, many design decisions were made to in order to maximize constructability while minimizing downside risk. Design details, developed in conjunction with experts from the University of Texas faculty, were more prescriptive than for typical U.S. projects. Beam reinforcement was specified, for example, so that standard lengths of bars could be used throughout the project: splice locations were not left up to the contractor’s discretion. Another detail of critical importance to the success of one prison was the isolation joint specified between special moment frame members and infill masonry walls. Here a workable solution had to balance structural concerns (enough space between infill and frame), facility function (not enough space that prisoners could escape or pass items between other rooms), and ventilation design (no air conditioning). Extensive review of submittals and on-site observations were required in order to make sure the contractor both understood the design and executed it properly. Thanks to the efforts of many professionals, it is our opinion that the facilities as constructed will serve the Haitian society for years to come.

The historic Hotel Commodore was designed by the famous structural engineer Homer G Balcom who also designed the Empire State Building. Built in 1917, it is located directly above and supported by the Grand Central Station railroad and subway structure below. In 1979 the hotel underwent major refurbishment before being reopened as the current Grand Hyatt. This paper will describe recent research and design work undertaken to accommodate major structural changes required to open up space and increase headroom at the subway mezzanine level to improve passenger flows. This involves underpinning and load transfer of the hotel structure above using temporary support, sequencing and jacking. The history of hotel and its famous designer will be documented together with commentary on the structural design and construction methods employed at the time.

The Moscone Center in San Francisco, CA, is the largest convention space in the region and a prime destination for a large number of conferences and corporate events. The convention center was originally designed and constructed during the late 1970s and early 1980s, and has since undergone several expansions and retrofits to increase its capacity and modernize its infrastructure. To modernize and maintain the competitiveness of the Moscone Center, the City of San Francisco, Department of Public Works, SF Tourism Improvement District Management Corporation and the hotel industry, have embarked on another major expansion of the popular convention center. The design team, which was led by Skidmore, Owings, and Merrill (SOM) and included SOHA Engineers and Tipping Structural Engineers (TSE), was tasked with adding approximately 305,000 sf of additional space below and above ground. A key part in providing the additional exhibition space was to connect and combine the underground portions of the existing North and South facilities below Howard Street, a main thoroughfare separating the two. To create the additional space and seamlessly integrate the two facilities, a 240’ portion of Howard Street will be excavated and replaced with a post-tensioned (PT) concrete box-girder viaduct structure. The design and construction of the Howard Street viaduct presents a variety of challenges that are addressed in unique and innovative ways. Typical considerations such as strength and deflections were complicated by long spans and heavy loads that resulted in a hybrid PT and mild-steel box-girder design. Further complications resulted from limited construction access below grade, adjacent to the viaduct. Faced with these challenges, the design team developed an elegant solution that satisfied the necessary structural requirements, is efficiently constructable, and optimizes the new usable exhibition space for the Center.

Cofferdams used in the coastal area have shown severe damages after typhoons including fracture of the steel piles, overturn and even total collapse. In order to enhance the understanding on the met-ocean conditions of the site and the wave pressure on the wall of cofferdam, extreme wave elevation was obtained through ultrasonic wave measuring instrument and wave pressure around the cofferdam were measured by 15 wave pressure gauges at 2 different water levels during Typhoon Dujuan (2015) swept across the bridge site. The measured wave elevations were analyzed with statistical method. Actual distribution of hydrodynamic pressure on the cofferdam was obtained from the measured wave pressures. Wave pressures on the cofferdam under regular wave were calculated by diffraction analyses using commercial hydrodynamic software ANSYS AQWA. The numerical simulation results were validated by the measured pressure on the cofferdam. The main conclusions of this study are: (1) extreme waves induced by typhoon Dujuan had reached the design wave height for the cofferdam, which might threaten the construction safety; and (2) diffraction analyses based on AQWA gives reasonable wave pressures, which allows for a faster preliminary evaluation of cofferdam.

Cooling towers are heat removal equipment for industrial processes. Major structural design components of an induced draft cooling tower include the reinforced concrete basin and sump channel. Revamp of an existing cooling tower system occurs when existing cooling system no longer meets the owner’s needs or when foreseeable profits will be earned through facility expansion. This paper presents the structural design challenges from a petrochemical industry’s propane dehydrogenation expansion project in the United States, of which the existing cooling towers and sump had to be upgraded in order to increase the polymer grade propylene production capacity by approximately 10%. These challenges included inconsistent design records, limited new construction spaces, underground obstructions, constructability issues, owner’s preferences, and delayed engagement of cooling tower supplier and water resources engineers. Viable structural engineering solutions, from the conceptual phase to the detailed engineering phase, were developed to deliver optimal benefits to the owner, such as the use of laser scanning technology, innovative design collaborations with all parties, and extensive engineering evaluations of existing conditions to reduce foundation sizes. Successes and lessons learned from this project experience are discussed and summarized.

Pipe racks are important structures in industrial plants. They are used within or to connect operating units, or longer distance for plant extension operations. For a large industrial facility, it can be feasible to utilize combined construction methods ‒ modules, pre-assembled units (PAUs) and/or stick-built construction at job site ‒ to fit site conditions, logistics, and construction schedule. Engineering design of pipe racks varies depending on specific construction methods selected, logistical and feasibility study results, constructability, piping routing, and layout of process units. Structural framing layout, selection of member sizes and connection types directly affect material selection, construction, cost, and schedule. In addition to the consideration of operating (product contents, thermal expansion and anchor loads) and environmental loads (wind and seismic), the design of pipe rack modules requires the consideration of sequencing during shipping (by barge/ship or truck), and self propelled modular transporters (SPMTs), and installation (by crane or SPMT) that associate with different design loads, load combinations and load paths. The purpose of this paper is to present the unique design considerations of framing layouts, member connections, and related structural analysis using different construction methods in new and existing facilities. Design considerations including transfer forces, camber, SPMT supports, temporary members, lifting details, member splices, brace connections and column base connections are also discussed and presented.

A three dimensional nonlinear dynamic analysis is performed for a single well observation platform. The structure consists of a single level service deck supported by three driven piles and a bracing frame. Extreme Loading for Structures (ELS) software was used. The analyses are carried out under the effects of impact for a 3500 ton vessel moving at speeds varying between 1 and 10 knots. The effect of soil type was investigated. The effect accidental failure of a supporting pile was studied and the possibility of progressive collapse of the platform was evaluated. The study found that there is a difference of up to 20% in the results using nonlinear dynamic when compared to the traditional equivalent static analysis. The analysis show that the soil type significantly affects the internal forces in the platform as well as the total platform displacement.

Nonbuilding structures located on soft soils are commonly supported on deep foundations consisting of a group of piles and a large pile cap embedded in the soil. The weight of the pile cap is often neglected in the seismic analysis of this system on the assumption that the inertia forces due to the pile cap can be directly transferred to the soil surrounding the sides of the cap. This paper provides an evaluation of conditions under which this assumption is valid and identifies the conditions when it would not be valid. Soil type, pile cap mass, passive pressure, side friction, backfill compaction, and pile resistance are addressed as contributing factors. A procedure for evaluating the amount of soil resistance acting on the sides of the pile cap under seismic loading was developed for this evaluation.

A major challenge in process industries is the constant demand to keep up with environmental regulations, which often require modifications to existing equipment, structures, etc. Most major modifications require some type of a shutdown period, which impacts production and loss of revenue. Engineering constructability solutions are what minimizes these shutdown periods, while keeping facilities within regulatory compliance. These case studies examine the challenges and solutions on a project which involved an oil refinery adding new flare gas recovery (FGR) modifications to reduce emissions on five (5) different flares. These modifications required the bottom portion of existing derricked flare stacks to be removed and replaced with new stack tie-in sections designed to reduce emissions. The objective was to determine a way to accommodate the new FGR tie-in installations without having to perform a total removal of the flare stacks. Some of the challenges included qualifying the existing structures to support the dead load of the flare as well as temporary wind loads, maneuvering new steel through existing structures and piping leading to irregular geometries, and using temporary steel plate mat foundations, in lieu of concrete foundations, due to geotechnical concerns and limited excavation clearances. The solution involved a combination of hydraulic jacks, reinforcing existing derrick structures, and new additional support structures down to grade. The solution saved the refinery significant time and money in additional down-time had a flare removal been required. In order to develop the solution, three-dimensional laser scanning and structural modeling was employed and a unique deflection controlled hydraulic jacking process was developed.

A refinery expansion project for Marathon Petroleum Company in Southern Louisiana required existing medium to large pipe racks to be expanded for additional capacity. Foundation modifications were necessary in order to add levels to the existing pipe racks. New piles were added and existing pile cap foundations were expanded. Several different pile types were considered. Custom designed helical piles were chosen, because they can be installed quickly with low overhead restrictions, produce minimal soil spoils, and are cost effective. The load capacity required for piles was higher than typical, off-the-shelf helical piles. In particular, the lateral load capacity demand was high due to wind loads of a hurricane prone region. Methods used to design and size helical piles are summarized including lateral pile analysis, bearing capacity calculations, and theoretical capacity to torque ratio estimation. Pile load testing was performed in order to confirm design capacities of the helical piles under axial and lateral loading. Measured axial and lateral deflections compared well with predicted values. This case history evaluates the effectiveness of modern helical pile design methods within the context of a real and practical example.

Increasingly, process plant modules are transported by sea from a module assembly yard to the plant site. Structural engineers and naval architects routinely collaborate to ensure that the module has sufficient structural strength to withstand inertial forces imposed by probable extreme motions during ocean transport. However, it is not only extreme motions that must be considered, because all motions will contribute to accumulation of structural fatigue damage. The module must be detailed to ensure that it has adequate fatigue resistance. This paper describes a relatively simple procedure by which the fatigue resistance of a module’s structural details can be assessed. The paper briefly describes the basics of fatigue damage assessment. It describes the data required from a naval architect for a simplified fatigue assessment of a module structure subject to vessel motions and includes results of such an assessment using criteria from AISC 360-10.

Ferry systems in the United States in large part rely on steel pile supported structures for berthing operations. However, as ferry vessels have increased in size and environmental regulations have tightened, the use of steel for ferry landing anchor piles has become far less cost effective. As a result, ferry owners are seeking alternatives for structures designed for vessel impact. The New York City Economic Development Corporation Citywide Ferry Service recently evaluated a program of adopting composite materials for use in all new ferry landing barge anchor piles. The anchor piles hold the floating landing barge in place and are responsible for absorbing the majority of impact energy from berthing ferry boats. The program planned to use the latest fiber reinforced polymer (FRP) pile technologies, materials, and production capabilities. Dozens of steel piles would be replaced with large diameter FRP piles, with reduced lifecycle costs and ferry service disruptions. The replacement is a large diameter, thick walled FRP pile installed by driving. Though recommended after a comprehensive study of possible options, the FRP replacement was ultimately introduced to the wider project too late to be priced competitively, and conventional steel systems will therefore be installed under the current program. Nevertheless, recognition of the value added and overall cost competitiveness of large diameter FRP piles is leading the technology to be considered for additional ferry programs now in earlier stages of planning.

The current wine industry standard of stacking four to five barrels tall is unstable during an earthquake strong ground motion event. Based on the damages observed from the 2014 South Napa earthquake, shows that barrels stacked four or five high were unstable due to failure from sliding and overturning. Seismic mitigation to current wine barrel stacking practice is not common in the wine industry. In this paper, an analysis of a moment frame steel structure to restrain the barrels was conducted using the equivalent lateral force procedure outlined in ASCE 7-10 Chapters 12 and 15. The linear time-history analysis procedure outlined in ASCE 7-10 Chapter 16 was also examined. Seven ground motions were used for the time-history analysis, including the 2014 South Napa earthquake. The barrels supporting structure is designed in accordance with both design procedures and results were compared. This paper presents an engineered solution to mitigate the economic loss due to seismic ground motions in the wine industry, create a safer work environment and to bring additional awareness to the hazard.

After loss of power and reactor cooling capability at the Fukushima Daiichi nuclear power plant due to an extreme seismic event, the U.S. nuclear energy industry developed a diverse, flexible approach to implement the lessons learned, called FLEX. FLEX builds on earlier safety steps by providing an effective and efficient way to make U.S. nuclear energy facilities even safer, by addressing nuclear regulatory commission (NRC) recommendations. These recommendations include systems such as additional layers of backup power by generators, battery packs, pumps, and air compressors in multiple on-site and off-site locations, to be available if all plant backup equipment is insufficient. A 21,000 gallon frac tank will supply backup water storage to reactors at a nuclear power plant during a beyond design basis event. This paper presents methodology for seismic structural analysis of the frac tank for two times the operating basis earthquake (OBE) and safe shutdown earthquake (SSE) response spectra including the Lindley-Yow method of analysis to properly account for the rigid response component. We performed fluid-structure interaction analysis using the computer program NASTRAN. Multiple tank fill conditions were considered, and evaluation was performed to ensure all component stresses were below allowable values per ANSI/AISC N690-12 and 350-10. The tank was evaluated for global stability using nonlinear sliding and overturning provisions of Appendix A of ASCE 43-05.

The behavior of cylindrical steel tanks in earthquakes has been documented during post-earthquake reconnaissance dating back to the 1977 San Juan earthquake in Argentina. Observed and documented damage to the tanks has been consistent through the 2014 South Napa earthquake and mainly entails: buckling of tank walls, anchorage failure, damage at locations of connecting piping, and racking of tanks against one another and against catwalk systems. Previous research on the topic has shown that nonlinear evaluation of the tanks is necessary in order to design tanks to withstand seismic demands. However, simplified procedures provided in the American Water Works Association Welded Carbon Steel Tanks for Water Storage (AWWA D100) remain based upon linear methodologies, e.g., elastic limits for lift-off displacements. Nonlinear procedures consider the formation of plastic hinges within the tank and therefore approximate more realistic lift-off displacements of the tank or pull-out forces on the anchorages. Researchers have demonstrated that post-buckling behavior of these tanks is stable and does not result in failure. This paper provides an overview of previous earthquake damage to cylindrical steel tanks used in the wine and water industries, as well as previous research that supports the use of more robust evaluation of these tanks to limit damage and subsequent failure during a seismic event.

The seismic design of rack structures according to the Rack Manufacturers Institute (RMI) MH16.1-08 standard requires calculation of the fundamental period in both the down-aisle and cross-aisle directions using “the structural properties and deformation characteristics of the resisting elements in a properly substantiated analysis” for seismic load determination. A detailed finite element model provides accurate calculation of the rack structure’s natural periods but can be tedious for large rack structures. The additional accuracy provided by the finite element approach can be impractical for evaluating large facilities containing several thousand storage racks. Approximate methods for computing the natural period of rack structures can provide simplifications that enable tractable solutions for large facilities. A discussion of approximate methods for period calculation, including approximate analytical methods and a reduced direct stiffness model, is presented with a comparison of periods computed using the approximate methods and the finite element method. The accuracy of each period calculation procedure is compared and the implications for the resulting design calculations are discussed for various rack structures. An analysis framework for systematically evaluating rack structures in large facilities using organized information about the rack structures with the approximate methods is also discussed.