Structures Congress 2018: Buildings and Disaster Management

An impediment to the use of seismic protection devices has been the difficulty for practicing engineers to design buildings with isolation system or damping devices. ASCE/SEI task committees charged with development of new generation of codes for seismic design and retrofit of buildings have updated the relevant code sections with one goal being to encourage the use of such devices. An effort was undertaken to develop a step-by-step design guideline for such design. Following the preparation of guideline, incremental analysis of four steel SMF building models was undertaken. The benchmark model was designed using the strength and drift requirements of ASCE 7-16. The other models were based on provisions of Chapter 18 of ASCE 7-16. For one model the lower base shear value was used, and for a third model, the drift ratios were further limited to obtain enhanced performance. Lower- and upper-bound analyses as required by ASCE 7-16 were conducted to size the dampers. The models were then subjected to incremental nonlinear analysis and key response parameters were evaluated. In all cases, the use of dampers resulted in reduction in the hinging of SMF members. It was notes that the best performing model was the model designed for 100% of nominal base shear and above minimum effective damping had superior performance, remaining elastic at design earthquake, and having almost no residual displacement at very large earthquakes.

In the event of sudden column removal, beam-to-column connections play a significant role in transferring the load carried by the damaged parts to the intact ones. This role involves experiencing a magnified bending moment and axial load which ultimately produces catenary action in the beam. This mechanism can eventually replace the flexural action in carrying the gravitational loading. Therefore, the beam and the connection must be able to develop and maintain a sufficiently large axial tension which explains the important role that connections play in mitigating progressive collapse. However, the strength and ductility of the out-of-plane members and connections affect the total load carrying capacity of structures employing moment connections. In this study, using component-based modelling, the effect of modelling these structural elements in the final result is investigated. Analysis results of a generic structure revealed that ignoring the out-of-plane members and connection can lead to overestimate the load carrying capacity of the affected span by 72%.

This paper investigates the seismic behavior of short dual systems–integrated moment and braced frames-considering the braced frame failure. Modeling of beams, columns, braces, and probable types of braces buckling are discussed in detail. Multi-story 3-bay moment frames were designed according to AISC-ASD 89. To ensure the shear performance of dual frames, moment, and shear displacement of frames are calculated and compared. To evaluate shear displacement of dual frames, shear displacement of moment, and braced frames are calculated separately and added together. These frames can be considered as a cantilever beam so moment displacement of dual frames is dependent on column sections. Therefore, the moment-area theory was used to determine the moment displacement. Buckling of the X-braces can be occurred in two modes depending on the lateral constraint of middle connection that is supplied by moment stiffness of tension braces and middle connections. When moment stiffness of tension brace is considerable and middle connection of X-braces has adequate rigidity, the buckling of braces occurs in second mode. Otherwise first mode overcomes the brace buckling. In this study, the results are obtained by the consumption of adequate moment stiffness of tension braces and middle connection rigidity. In order to consider the stiffness degradation that is caused by gravity load, P-Δ effect, corotational theory is used and pushover curves are compared considering the ultimate and residual strengths. Braced frames buckling includes elastic and inelastic depending on the slenderness ratios. Euler and Belayesh relations were used to evaluate critical strength of braces in elastic and plastic regions respectively. Nonlinear static analysis was conducted on the frames considering braces failure using OPENSEES platform with displacement control pushover analyses on all designed frames. In other words, according to consumption of rigid diaphragm of all stories, one of the roof nodes was pushed up to 3% of the frame height. The load pattern of pushover analysis was chosen adverse triangular. The results indicate that brace failures occur at 2% drift of corresponding stories. In this paper during the pushover analyses, 16, 64, 144, and 1024 pushover analyses were done on 2-, 3-, 4-, and 5-story dual frames subsequently. Pushover curves corresponding with the same story braces failure in each frame are averaged. The results of pushover analyses on short dual frames indicate that the best performance of frames, considering the ultimate and residual strengths, are obtained with brace failures occurring in higher stories.

This paper compares the cost effectiveness and predicted seismic performance using a moderately-ductile (“Intermediate”) steel moment frame (IMF) with the cost and performance using a highly-ductile (“Special”) steel moment frame (SMF) for a large canopy structure at a hospital site, located in Seismic Design Category D in California, and considered an essential facility. Material and construction costs associated with IMF and SMF systems were compared based on actual project costs and national commercial cost data. The comparison showed that the higher response modification factor, R, associated with the SMF, reduced structural member sizes and material costs, as expected. Costs associated with seismic performance were predicted using the FEMA P-58 methodology. The results indicated that both the IMF and SMF systems performed similarly in terms of repair time. In terms of repair costs, performance was mixed. For the IMF system subjected to design basis earthquake (DBE) ground shaking there was an 11% chance that the canopy would be deemed unsafe.

This paper describes a study to determine the suitability of vehicle shock absorbers for use as seismic protection devices. Studies of various types of supplemental damping devices have shown that there are particular benefits to using viscous fluid dampers (VFD’s) for seismic protection. Vehicle shock absorbers have similar mechanical properties to VFD’s that, in theory, make them a viable alternative. In addition, the low cost of vehicle shock absorbers makes them attractive for use in lower budget projects. Using models of vehicle shock absorbers that are available in the literature, a comparison is made between the behavior of shock absorbers and VFD’s when they are subjected to harmonic motion. The comparisons indicate that vehicle shock absorbers can be configured to provide response characteristics that are similar to VFD’s, thereby suggesting their potential application for seismic protection of structures. The overall goal of the research presented herein is to identify vibration control devices that could be used for low-cost seismic protection. To accomplish this goal, a suboptimal design objective is proposed wherein the protection system provides sufficient protection, although not optimal, while incurring low cost. The suboptimal design process begins with identifying suitable vibration control devices that are readily available (off-the-shelf units that are mass-produced with associated cost reduction). This paper describes this first step in the suboptimal design process.

Cyclic flange local buckling typically occurs when plastic hinges form in the beams and columns of special moment resisting frames subject to seismic shaking. The buckling response is affected by the significant fluctuations in axial stress that occur in such members. While local buckling in beam plastic hinges has been thoroughly investigated in the past for monotonic loading situations, the effect of cyclic flange buckling on member capacity is not yet well understood. In order to address this shortcoming, ten half-scale T-section specimens are tested under cyclic axial loading in a configuration intended to replicate the cyclic demands imposed on flanges in the plastic hinge region. The main experimental variables are the flange slenderness ratio, web restraint (varied by changing the slenderness ratio of the web of the T-section), and type of loading (monotonic versus cyclic). Test results show that the flange slenderness ratio significantly affects the degradation of axial strength as the applied deformation increases. The rates of strength degradation under both monotonic and cyclic loading schemes are compared and the results are used to evaluate current seismic design requirements for local stability of steel structures.

Finite element analysis involves inherent approximations and numerical errors. In addition to these, the increasing size of structural models and the use of automated workflows for creating them can lead to hidden user errors in the said models. For the engineer to have confidence in analysis results, it is necessary to be aware of how these errors manifest themselves in models, what impact they have on analysis results, and, most importantly, how they can be detected. We present novel numerical techniques that the analyst can use to ‘debug’ their models and verify the accuracy their analysis results. These techniques have been implemented in software and have been successfully used by practicing engineers working on live projects.

The coupling of modern architectural designs with digital parametric tools has resulted in non-planar structures and facades with extreme curves. As a result, structural engineers are routinely designing elements that are curved in 2 or 3 dimensions. While these structural elements can often be discretized into a series of straight elements that approximate the curve, or analyzed using detailed finite element models, it is often necessary to design curved structural elements to accurately account for combined stress behavior due to coupled forces. As a result, it is desirable to provide practicing engineers with a series of design charts and closed-form equations to facilitate early-stage topology decisions with accurate and convenient tools. The closed form solution for 2D beams curved in-plan is well known and readily found in most undergraduate mechanics texts. However, the topic of 3D curved beams (i.e., helicoidal beams) has not been addressed in the literature for applications involving steel beams and girders. As a result, engineers typically design helicoidal beams by considering only the strong-axis moment through the vertical projection of the beam and resolve it into a fixed ended, 2D curved beam. However, this approach is approximate and not necessarily conservative since it neglects the coupled effects of stresses due to geometry. This research presents a numerical model for converged discretization of a helicoidal beam and subsequent use of the convergence criteria for a series of parametric studies. The results are plotted and curve-fitted to provide simplified design equations for a variety of different cross-sections and stair geometry. The results of individual stresses show good agreement (within 6%) with analytical models and resulting design values.

The purpose of this study is the development of an analytical methodology to describe the response of typical building gravity systems subjected to an interior column removal scenario. The proposed methodology accounts for two collapse mechanisms, termed as the “yielding-type mode” and the “stability mode”. The former is a ductile mechanism comprised by multiple shear connections failure and extensive yield of the wire mesh and the steel deck, while the latter is a brittle collapse mode triggered when one column of the building loses its stability and buckles. The method is based on a series of elastic analyses in appropriately selected geometries of the structure, rendering the method a very easy tool to be perceived and applied. The analytical methodology is implemented to a typical 9 story steel framed building and validated against finite element models of the building, conducting column removal scenarios from the 1^st to the 9^th story. Comparison of the results reveals that the method can accurately estimate the collapse mechanism and provide adequate insight on damage propagation up to the ultimate collapse load.

When executing major modernization of existing buildings besides the challenges of adapting new mechanical equipment and architectural elements, the greatest challenge can come from updating the structural frame to resist current code prescribed lateral forces. As research and testing results in the evolution of building codes, new design forces often exceed the limits of the lateral force resisting systems for older buildings. As great a challenge there is of upgrading the structural system, often the most expensive impacts are related to the time required, and impact to the existing occupants to remove and reconstruct architectural elements. This paper highlights a project where preliminary studies based on traditional methods of analysis indicated the need to perform major structural upgrading as part of the building modernization effort. Due to the requirement of maintaining full occupancy and the estimated costs for the effort, an alternative performance based analysis was performed. These included both simplified methods to prove the concept, and ultimately more advanced methods to verify the expected outcome. The analysis utilized non-linear push-over and time history analyses typical of those for high level earthquake loads for a structure exposed to hurricane forces. Loads were developed using wind tunnel analysis to simulate a one-hour event with a 0.2 sec time step. The result was that no structural upgrading was needed, thus saving the project approximately $20 million. This topic is of international interest. It advances the science of wind engineering beyond standard building code requirements. It demonstrates the resilience inherent in structures that is generally unaccounted for in day-to-day design.

Friction dampers dissipate energy through the friction that develops between two solid bodies sliding relative to one another. When a major earthquake occurs, the friction dampers slip at a predetermined load before yielding occurs in the members of a frame, which dissipate a major part of the energy. It saves the initial cost of new construction or retrofitting of existing buildings, with a very high energy dissipation. In this paper, the seismic performance of a 14 story moderately ductile concrete frame, designed based on the current edition of the National Building Code of Canada (NBCC) has been studied with and without friction dampers. The building is assumed to be located in Victoria, BC, in the western part of Canada. Nonlinear dynamic time history using a set of ground motion records has been performed to determine their effects. The costs of the building frame with and without friction dampers have been evaluated for comparison. The seismic performance of the building in both cases have been evaluated using nonlinear dynamic analysis and the building with dampers has been found to achieve the desired level of performance without any significant damage in the frame.

Spanning structural trusses are very common items designed by engineers. Whether these are floor/roof trusses or foot bridge trusses, long or short they all have similar design approach. Engineers often are forced to use intuition or rules-of-thumb to arrive with an efficient truss type (Warren, Pratt, or other) or efficient depth to span ratio for a given load/span condition. After selecting and sizing an initially selected truss often little to no attempt is made to study other out of the box solutions to reduce structural quantities. If this is a typical floor truss in a multistory building a small saving in one truss can quickly multiply into a significant number worth an extra effort. In this paper, a method is presented that minimizes the effort of selecting the right solution. It appears that simple design aiding diagrams can be created and used in general situations. These diagrams can be easily used to estimate structural quantities before the truss is even designed. Also, if: load, span, and deflection criteria are known, an optimal depth and type of truss can be quickly established. In the process to generate these design charts it is important to consider stiffness requirements together with strength criteria to obtain most efficient design. Such diagrams can also be used to estimate a penalty on structural quantities when a design is forced away from the optimal. This paper provides a few sample truss design diagrams generated based on the theoretical derivations presented in this paper.

The design of pedestrian bridges has been evolving significantly in the past few years due to emerging technologies and the application of non-traditional materials. This paper describes these trends with specific reference to the design of a prototype for the Los Angeles LAX airport pedestrian bridges. The design for the bridges was developed using structural optimization techniques, which have already been successfully applied in the aeronautical, automobile, and mechanical industries where natural force flows are modeled. These fundamental principles of optimization have been used to develop two novel responses to the long-span pedestrian bridge – the optimized orthotropic plate pedestrian bridge and the optimized truss pedestrian bridge. Both designs, though unique and simple, integrate the idea of topology optimization with modular design, resilient materiality, sustainable practices, and visual transparency.

The optimization of the design of a structure system can lead to significant cost savings and improvement to the function and reliability of a facility. However, it is often necessary to employ methods beyond the provisions outlined in building codes and standards in order to effectively optimize a design. This is clearly highlighted when considering the effects of snow on a structure. As building geometries and structural systems push the boundaries of conventional design, a strict application of the code is not necessarily synonymous with an optimized structural design as a result of inherent generalizations. Further, building codes and standards do not provide guidance for assessing and mitigating risks associated with snow and ice that may slide and/or fall from a structure. This paper explores the design process and analysis methods that were employed in the design for snow related concerns for the U.S. Bank Stadium in Minneapolis, Minnesota. Consideration of the various aspects of snow related concerns lead to design modifications that resulted in significant reductions in both the structural steel costs and potential risks associated with snow and ice that may fall from the structure.

The National Institute of Standards and Technology recently expanded its large-scale structural-fire testing capabilities in the National Fire Research Laboratory. A landmark test series is being conducted on long-span steel-concrete composite floor beams designed and constructed following U.S. building codes and standards. The test program consists of five 12.8 m span composite beams with one of two types of shear connections: bolted/welded double-angle connections or single plate shear connections. Two of the five specimens have slab continuity at the beam ends. This paper presents the results from a recent test on the composite beam conducted at ambient temperature. The experimentally measured behavior and flexural moment capacity will be used as a baseline to compare with the composite beams still to be tested under combined mechanical and fire load. The datasets produced are providing technical information necessary to advance performance-based design of composite floor systems in steel-framed buildings subject to fire.

The objective of this study is to develop a unified mechanical model that can be considered as a practical tool for designing steel connections for professional structural-fire engineers in the U.S. The proposed model is capable of predicting the behavior of two widely used simple steel connections (shear tabs and double angles) when subjected to fire temperatures. It incorporates the connection rotation of key component elements, and the nonlinear behavior of both bolts and base materials at elevated temperatures. The model includes linear and nonlinear springs, which predict the strength, stiffness, and rotational capacities of each connection component. The proposed model is validated against experimental results available in the literature under steady-state temperature analysis. The model covers all possible limit states and governing failure modes under different loading and temperature conditions. The model can be used to develop fire design guidelines for simple beam-column connections in fire.

A series of experiments is being conducted on five 12.8 m long composite floor beams at the newly-commissioned National Fire Research Laboratory at the National Institute of Standards and Technology. The test beams were designed according to current U.S. building codes with input and design-review provided by panel of expert practitioners. Each specimen consists of a W18×35 beam and a 1.83 m wide lightweight concrete slab cast over profiled steel deck units. Composite action between the steel beam and concrete slab is achieved using 19 mm diameter steel shear connectors spaced at 305 mm on center. One of the five specimens was tested at ambient temperature to measure its behavior and flexural strength, and to verify the purpose-built mechanical loading system. The remaining four specimens will be tested under simultaneously applied mechanical loading and an enclosure fire using a natural gas fuel delivery system. The beam-to-column connections and rotational restraint of the slab ends over the support girders were varied among those four specimens.

When completed in 2019, 2044 Franklin St. in Oakland, CA, will be the tallest structure in the U.S. utilizing prefabricated prefinished volumetric construction (PPVC) as an alternative to conventional construction methods. A vertically integrated team of AEC professionals in collaboration with manufacturing experts designed a modular system suitable for a mixed-use tower of this size. The structural engineering team developed a unique structural system comprising a steel plate shear wall (SPSW) core supplemented with buckling restrained brace (BRB) outriggers to provide a ductile response to severe West Coast earthquakes. This structural system not only complied with the architectural and rentable space requirements, but also helped to maximize off-site construction and to minimize the on-site labor work. The use of performance based design in conjunction with full-scale testing of some of the critical structural components helped to establish a compatible lateral story drift ratio of up to 2.75% at MCE level for the modular gravity space frame. The primary energy dissipation mechanism is envisioned to be a combination of steel plate shear wall post-buckling tension field action and BRB yielding. The proposed structural system translated to substantial material savings up to 30% and improved the construction speed by 6 months compared to conventional structural systems and construction methods.

Performance-based design (PBD) has been widely accepted as the new design paradigm to reduce the risks to engineered facilities. In this paper, an innovative PBD approach for wind excited tall buildings equipped with high performance control systems (HPCS) is proposed. Maximum acceptable accelerations are introduced as target performance for HPCS design under atmospheric boundary layer winds. The wind hazard is characterized by mean recurrence intervals of the wind speed, representative of low, medium, high, and extreme events. A life-cycle analysis procedure is integrated in the PBD to estimate the total costs of the structure, accounting for initial construction cost, installation and maintenance costs of the devices, and savings associated with wind-induced vibration mitigation. The proposed methodology is applied to a numerically simulated 39 story building, located in Boston, MA, equipped with passive and semi-active devices. To address the variability in the wind excitation, different realizations of the same wind velocity are generated and used to develop fragility functions for the structure. Results show that both the passive and HPCS cases offer significant financial benefits over the lifetime of the structure. Results show that both the passive and HPCS cases offer significant financial benefits over the lifetime of the structure. The mean annual failure costs resulted similar, while the HPCS, compared to the viscous case, yielded to a higher life cycle cost, due to the higher initial and maintenance costs associated with the HPCS devices.

Seismic risk assessments are essential for the property and casualty insurance and many public entities at the national and local levels; however, comprehensive studies for large portfolios and in seismically active regions often become time-consuming processes and require significant computational resources to run the required simulations. This research introduces surrogate models which are developed by random forests, a class of nonlinear statistical learning algorithms, to significantly reduce the computational requirements in exchange for manageable errors in predicting the portfolio losses. To demonstrate the application, a portfolio consisting of four different building classes is simulated in OpenQuake, an open-source platform for seismic risk analysis. The developed surrogate model is shown to save close to 70% of the computation time and predict the portfolio losses for small to mid-range events with small errors but underestimates the values for very large events. A similar method can be applied to develop parametric solutions.

The 2008 New York City Building Code introduced the requirement for structural peer review of buildings meeting one or several special characteristics such as: aspect ratio of seven to one, taller than 600 feet, more than 1,000,000 square feet, etc. Based on the author’s observations of some 38 peer review reports, the paper presents an analysis of several report elements–level of effort and reporting, relationship between engineer of record and peer reviewer, typical findings. The effect of the reports on the individual project and on the structural design community is discussed. In general, for these tall buildings there are two special areas of difficulty–foundation and wind design. Both are based on respective specialist reports. While the peer reviewer is expected to verify the conformance of the design with the soil and wind tunnel reports, these reports may not subject to a peer review.

American Institute of Steel Construction (AISC) document 360, Specification for Structural Steel Buildings, is the basic reference for the design, fabrication, and erection of structural steel buildings and other “building-like” steel structures in the United States. When applied in conjunction with AISC 360, AISC 341, Seismic Provisions for Structural Steel Buildings, is the standard reference document for the seismic design of steel structures throughout the United States. Balloting is complete to update AISC 341-16 that will be incorporated with ASCE 7-16 and AISC 360-16 into the 2018 International Building Code. The document will have significant technical modifications including new material specifications, use of steel braced diaphragms, new column splice details, requirements for SCBF gusset plate welds, and application of demands on columns that participate in intersecting frames. In addition, significant new provisions related to the seismic design of multi-tier braced frames will be provided. A new composite shear wall system has also been developed. This paper will summarize the changes proposed for AISC 341-16.

The collapse potential of a four-story steel special moment frame (SMF) under a set of ground motions is evaluated using high fidelity computational simulation. The SMF is designed in accordance with current design requirements and employs reduced beam sections and deep columns. The computational model is capable of explicitly accounting for the interaction of local and global instability within the SMF. A study is performed to investigate the effect of the level of gravity loads on the collapse response of the frame. Even though all columns satisfy highly ductile requirements in current seismic provisions, they become increasingly vulnerable to global buckling as the gravity-induced axial load increases.

Design optimization of building structures are usually performed by minimizing an objective function defined as total weight or cost of material. The building code strength requirements or drift limitations are defined as optimization constraints. The violated constraints will be added to the main objective function after adjustment by a weight factor. This objective function is often not differentiable since the violated constraints change at every iteration. Plus, the weight factor that adjust the violated constraint with the main objective function can affect the optimization results and its value may not be reasonably justified or substantiated. In this paper, a new structural design optimization is proposed for shear wall building structures. The objective function for this optimization process is defined based on the estimated demand to capacity ratios of the shear walls. Other design criteria such as drift limits or link beam designs are also considered, but are not directly included in the proposed objective function. By pushing the demand to capacity ratios to the possible highest, the thicknesses of shear wall are reduced. The proposed objective function is derived by assuming a beta distribution for the shear force demand to capacity ratios of the shear walls. Monte Carlo samples are generated to find the maximum of the objective function and for sensitivity analysis. The optimization framework is applied on a 70 story building. The correlation between the proposed objective function and the cost associated with the lateral system is presented. The generated Monte Carlo samples are also used to design the shear wall thickness at different level of conservativeness.

Steel plate shear wall (SPSW), which commonly consists of an unstiffened slender wall panel inside a steel boundary frame, is known as an effective lateral force resisting system in high seismic zones. However, in accelerated construction of high-rise buildings, gravity loads will inevitably be transferred to the wall panel and causing elastic buckling, since it is impractical to fasten all the wall panels to the boundary frame in the last step. In order to avoid buckling of slender wall panels under gravity or in serviceability limit states, channel stiffeners are attached to the wall on one side, with both toes welded to the wall surface to form a closed section and provide higher out-of-plane and torsional constraints. This paper presented experimental research on channel-stiffened steel plate shear walls as a new type of steel plate shear wall system. Cyclic quasi-static tests were conducted on three 1/3-scale two story single-bay specimens, including two specimens with different stiffener arrangement and a similar unstiffened SPSW specimen for comparison. All specimens showed highly ductile behavior and stable cyclic post-buckling performance, and could tolerate at least 4% story drifts. Compared with unstiffened SPSWs, the channel stiffened steel plate shear walls could have higher elastic buckling capacity and lateral strength and significantly higher lateral stiffness. Recommendations on seismic design of stiffened SPSWs were also proposed.

There is a lack of discussion in the most recent building codes such as ACSE 7-10 and ACI 318-14 and the most recent committee documents such as ACI 369.1 and ASCE/SEI 41 regarding the effect of the floor openings on in-plane behavior of low-rise reinforced concrete (RC) buildings with long and narrow plans. Results of this paper emphasizes the importance of the stated problem by indicating that the flexible in-plane behavior in such low-rise buildings where the lateral resistance is provided by the end shear walls is likely. Building macro-models using ETABS, capable of simulating the flexible (semi-rigid) behavior of concrete floor diaphragms using shell elements, were created for such buildings to evaluate the effect of the openings on the response of the building to seismic loads. Results show that this behavior (floor flexibility) is more pronounced even when small openings are present at the center panels of the floor diaphragm, where floor flexibility places excessive demands (deflection and stress) on floor panels with opening. Additionally, based on the nonlinear finite element analysis of floor panels with openings (micro-model), it is shown that openings can significantly reduce in-plane load-carrying capacity of slab panels, thus, new recommendations are presented to improve the in-plane capacity of RC slabs with openings.

Design of reinforced concrete columns and shear walls is an iterative process. The capacity of an assumed section is checked using interaction diagrams and the procedure continues until a satisfactory section is found. This study introduces “Direct Design” method and “Design Diagram”. Direct design method is an analytical approach by which the required area of reinforcement is determined directly without using an interaction diagram. This method provides a fitted solution for a reinforced concrete section; the capacity of the section is equal to the applied load and moments. For each column or shear wall, many fitted section with different sizes and bar arrangements could be. A design diagram shows all possible fitted sections for a column or shear wall. This study provides an algorithm for making design diagrams.

Wood is one of our most sustainable materials. It requires less energy to harvest, mill, and deliver to the project location than steel, concrete, masonry, or other materials. Timber products sequester a significant amount of carbon in comparison to the amount of carbon released during harvest, manufacture, and transport. Timber structures have generally performed well in earthquakes and wind storms if constructed according to the building codes and good construction practice. Timber structures often have a cost advantage over other types of structures. These advantages are lost when timber structures fail prematurely and the structure needs substantial repair or replacement early in its life cycle. Many forensic studies have been made of single structures, but these studies have not been performed using consistent criteria or methods nor have the conclusions been examined with respect to other structures. Often authors of these studies at engineering conferences are not experts in wood and fiber science. This paper examines and classifies the types of defects seen in timber structures, and provides recommendations that practicing engineers can use to reduce or control these defects. Learning from the mistakes and the design errors of others are fundamental methods used to improve structural design. Structural engineers of the future need to reflect on the knowledge derived from the past. Lessons learned from these studies can lead to reduced defects in the future and to enhancing the sustainable nature of wood construction. This paper will broaden the knowledge of practicing engineers to assist them to be experts in sustainability and good stewards of materials and the built environment.

A sixteen-story steel frame structure is proposed to be built on an existing twelve-year old one-story reinforced concrete structure which is supported on an isolated footing foundation system. Original concrete mixture information and material testing records were not available to the project team. In order to determine if the existing reinforced concrete structure had sufficient capacity to carry the load from the proposed steel structure, the in-place concrete compressive strength of three footings and twenty-nine plinths was estimated using post-installed concrete pullout test and core compressive strength test. The test results indicated that the pullout force had a strong correlation with the core compressive strength. The estimated concrete compressive strength of footings and plinths using pullout test was found to be structurally adequate. With the use of post-installed pullout test, the project team was able to determine the structural capacity of existing structural members without causing significant delay in the project schedule.

Reinforced concrete shear walls play a significant role in seismic areas. It is important to have a ductile failure in the shear wall instead of brittle failure. Many experimental and theoretical tests have been conducted on shear walls without openings, but this project focused on the performance of shear wall with a different pattern of staggered openings under lateral loading. In this research paper, the failure analysis of reinforced concrete shear walls with vertically ordered openings and three walls with different openings angles is conducted under incrementing increasing lateral load using ABAQUS program. The final results of this project are compared to experimental results. Due to a limitation of the test setup, the models were reduced to a 1:4 scale, and the failure modes of a 4-story wall with 4 different opening angles were modeled.

Metal plate connected (MPC) joints are commonly used in modern timber truss construction. These joints are typically constructed using light gage steel plates with teeth that are pressed into 2x truss members to form connections. These connections are often modeled as either pinned or fully fixed. Partially rigid connections are sometimes modeled but the amount of rigidity that should be used is not well understood. Analytical models for the bending rigidity of MPC joints were developed based on experimental testing of several MPC connections. A simplified method for determining the rigidity of MPC joints was developed so that more accurate values can be used in analysis software.

This paper presents a study of masonry reinforcement using fiber grid. A reinforcement system was proposed and initially studied through numerical analyses. Several masonry specimens implementing the fiber grid reinforcement were constructed and tested on a shake table. A comparison of the results from numerical analyses and physical testing found good agreement. Fiber grid reinforcement appears to significantly improve the lateral load resistance of masonry structures. The system can be designed and implemented relatively easily and economically on both existing and new buildings to enhance their seismic resistance.

End cover separation and shear crack debonding are the two most critical modes of failure in RC beams retrofitted with steel plates or carbon fiber reinforced polymer (CFRP) composite plates due to the brittle nature of the failures. In this paper, a 3D finite element analysis was used to simulate the peeling failure of strengthened beams using either smeared and/or discrete crack approaches. The effect of the thickness, stiffness, and length of the bonded plates and adhesive layer were investigated in this paper. Also, the effect of concrete cover replacement on the peeling failure was studied. Extending the CFRP plate length to 55% of the shear span enhanced the ultimate load capacity by over 200% compared to the un-strengthened beam. Further extension of the CFRP plate in the shear span had little effect on the flexural capacity of the beam. Beams with concrete cover replacement had higher ultimate load and deflection and bending stiffness than strengthened beams without cover replacement.

The use of high-strength concrete (HSC) is continuously increasing due to its mechanical and durability advantages over normal-strength concrete (NSC). In high-rise buildings, HSC can reduce the dimensions of the lower-stories columns, which makes it a more cost-effective choice for builders than NSC. Studies have shown, however, that HSC is more brittle in compression than NSC and that the confinement provided to HSC is less effective than in NSC. Therefore, greater confinement is required for columns made from higher strength concrete to achieve similar strength and ductility enhancements. This behavior is the main obstacle to HSC’s widespread use. While the ACI 318 standard does not limit the concrete compressive strength, the Eurocode 2, the New Zealand standard 3101, and the CSA A23.3 standard limit the maximum strength that can be used for seismic design to 90 MPa, 70 MPa, and 80 MPa, respectively. Moreover, studies have shown that the axial load level has a significant influence on the ductility of concrete columns subjected to cyclic flexure and constant axial loads. A large number of studies were performed to examine the behavior of HSC columns subjected to compressive loading and to combined constant axial load and reversed cyclic flexure simulating earthquake loading. The main drive for this study was to give recommendations for the confinement reinforcement ratios required for HSC columns in a real 60-stories high-rise building. First step in the study was to compare the confinement requirements of several international standards. Since it is the first experience in Israel to use HSC for a commercial RC multistory building, the next step was to design and perform experimental study on large-scale HSC circular columns subjected to compressive loading with different volumetric transverse reinforcement ratios. The results show the differences between the standards requirements and give an insight on the recommended transverse reinforcement ratio for columns that behave as secondary structural elements, which are not designated as part of the seismic-force-resisting system.

Advanced framing (sometimes termed smart framing or optimal value engineering) resulted from efforts in the structural community to use less wood in the framing of residential construction. Through use of larger studs at greater spacings, reduced lumber in corners, single instead of double top plates, and other modifications, lumber is reduced. This also theoretically allows for more insulation in the building envelope. This paper describes efforts to build two residences side by side-one with traditional framing concepts, one with advanced framing, including innovative header designs and details. The paper will describe the structural details, presenting the lessons learned about installation with available contractors, lumber usage, and other important information. In addition, energy data is presented, allowing the benefits of the innovative structure to be seen through comparison of sustainability metrics.

Ports are located in areas prone to sea level rise and storm surge with past hurricanes having highlighted their vulnerability to extreme forces due to storm surge and waves. However, models are still lacking to examine the fragility of these structures subjected to extreme forces that occur in coastal storms. This study adopts a recently proposed analytical framework for rapid estimation of the fragility of wharves/piers subjected to storm surge and waves. A typical deck-pile connection is selected considering two cases, i.e., dowels developed above and below the deck’s top mat reinforcement. For each aforementioned case, four scenarios are examined for the predicted wave load, i.e., two scenarios related to deck configuration and two scenarios related to impact force prediction. Then fragility analysis is conducted to estimate the probability of deck uplift conditioned on select hazard intensity measures. Monte Carlo simulation with Latin hypercube sampling is used for propagating uncertainties in parameters affecting both structural capacity and demand of these connections, e.g., uncertainties in material properties, wave forces, and model error. The results indicate that the maximum difference in the uplift probability between the two deck configurations decreases in an almost linear trend with the decrease of the surge elevation. However, alterations in the surge elevation do not significantly affect the maximum difference in the uplift probability between the two prediction methods. Internal connections have a smoother transition to uplift failure indicating that uncertainty in parameters related to their capacity and demand plays a larger role compare to the seaward ones. Finally, to effectively reduce the fragility, dowels should be anchored above the deck’s top mat reinforcement for dowelled connections exposed to coastal hazards. Future studies will include effects of climate change, different deck configuration and epistemic error in wave load models with illustrative case studies in the Houston Ship Channel, i.e., applying the fragilities with representative storms having alternative intensities and sea level conditions.

In the past year, major flood events in the U.S. have resulted in more than $46 billion in damages to housing and infrastructure. This trend is expected to remain as extreme weather events are predicted to occur more frequently. The Federal Emergency Management Agency (FEMA) Building Science Branch is working with ASTM International to develop tools for evaluating flood damage resistant materials. The recently published, Standard Test Method for Water Immersion and Drying for Evaluation of Flood Damage Resistance (ASTM E3075), exposes construction materials to water immersion and drying conditions to simulate the effects of wetting and subsequent drying that occurs with a flood event. The wetting and drying exposure is followed by surface cleaning. The Standard Practice for Determining the Flood Damage Resistance Rating of Materials and Assemblies, which is being developed under ASTM WK35237, includes descriptions of testing parameters for evaluating the material’s ability to be cleaned and restored to serviceability. The primary users of these standards will be product manufacturers, building designers, and building officials seeking criteria for determining what materials are allowed to be used in construction below the base flood elevation (BFE).

Population centers in Texas are some of the fastest growing regions in the country. As land development expands in these regions, structural engineers will be confronted with the obstacle of designing structures that are capable of resisting the expansive clay soils that are prevalent in these areas. New technologies are available on the market today to combat expansive soils in efficient and effective ways. As innovations continue to be developed, structural and geotechnical engineers will be tasked with familiarizing themselves with these unique products and methods in order to provide these technologies for their clients. Developers and homeowners will begin demanding these new methods that could save them money, time, and anxiety either during the initial construction phase or over the lifetime of the structure.

In this research, the effect of soil-structure interaction (SSI) on seismic inelastic displacement ratios of SDOF systems is investigated for the case of single and repeated earthquakes. To account for the effect of SSI, a simplified equivalent fixed-base method is proposed based on FEMA guidelines. NEHRP soil types C and D were considered for different foundation aspect ratios and different structure strength reduction factors. Different models from the literature are adopted to account for the effect of repeated earthquakes. A well-defined degrading model was used to conduct the dynamic analyses. A total of 100 earthquake records, including recent ones from Japan and New Zealand, with magnitudes greater than 5 and peak ground acceleration (PGA) values greater than 0.08 g, were selected and scaled to the same hazard level. The effect of aftershock and pre-shock was included in the analysis. These earthquake records were applied on five RC columns that were chosen from the Pacific Earthquake Engineering Research Centre database. A large number of dynamic analyses were conducted to derive the required inelastic ratios. Different strength reduction factors, foundation aspect ratios, and repeated earthquake models were assumed for a range of NEHRP soil types C and D properties in the study. The results show that inelastic displacements are greatly affected by both the soil flexibility and the effect of repeated earthquakes. The large collected data was used to derive mathematical expressions for inelastic displacement ratios, suitable for use in performance-based seismic evaluation in a design office. A simple expression was proposed to properly account for the different parameters influencing the behavior. Current performance-based seismic design guidelines of structures do not take into account the effect of soil-structure interaction or that of repeated earthquakes. This research fills this gap through a comprehensive numerical study that considers all relevant parameters.

This paper evaluates the consequences of practicing soil structure interaction (SSI) regulations of ASCE 7-16 on seismic performance of building structures. The motivation for this research stems from the significant changes in the new SSI provisions of ASCE 7-16 compared to the previous 2010 edition. Generally, ASCE 7 considers SSI as a beneficial effect, and allows designer to reduce the design base shear. However, literature shows that this idea cannot properly capture the SSI effects on nonlinear systems. ASCE 7-16 is the first edition of ASCE 7 that considers the SSI effect on yielding systems. This study investigates the consequences of practicing the new provisions on a wide range of buildings with different dynamic characteristics on different soil types. Ductility demand of the structure forms the performance metric of this study, and the probability that practicing SSI provisions, in lieu of fixed-base provisions, increases the ductility demand of the structure is computed. The analyses are conducted within a probabilistic framework which considers the uncertainties in the ground motion and in the properties of the soil-structure system. It is concluded that, for structures with surface foundation on moderate to soft soils, SSI regulations of both ASCE 7-10 and ASCE 7-16 are fairly likely to result in a similar and larger structural responses than those obtained by practicing the fixed-base design regulations. However, for squat and ordinary stiff structures on soft soil or structures with embedded foundation on moderate to soft soils, the SSI provisions of ASCE 7-16 result in performance levels that are closer to those obtained by practicing the fixed-base regulations. Finally, for structures on very soft soils, the new SSI provisions of ASCE 7-16 are likely to rather conservative designs.

Micropiles are an economical foundation solution for projects that have access constraints and low headroom conditions. Conventional piling techniques can be expensive or even impossible in these types of situations when foundation upgrades are required. Micropiles have been used to retrofit existing foundations due to under design of existing foundations or to upgrade existing foundations for added load. This paper will discuss three case studies where micropiles were used to retrofit existing buildings. The first project is a parking garage in Lake Highland, Texas, where 36 micropiles were used to remediate 12 of the existing failed parking garage column piers. The second project is a fifty-plus year-old building in downtown Dallas, Texas, that involved the conversion of an existing basement into a parking garage. It required 5 micropile to underpin an existing wall footing that was to be undermined for ramp construction and 6 additional micropiles to support three new wall columns created within an existing wall to allow the passage of cars. The third project was the expansion of an existing coliseum, micropiles were used in combination with structural bracing and permanent soil nails. The new foundations were installed within the project schedule and will provide long-term support for all applied foundation loads.