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Past research efforts have developed several self-centering beam-to-column connections for minimizing structural damage in steel moment frames after severe earthquakes. However, less focus has been on low-damage column base connections. Severe damage at the base of columns in conventional steel structures with moment frames is likely during an intense earthquake, rendering the building nonresilient. This paper evaluates the application of a recently developed viscoplastic damper in low-damage column base connections. The proposed viscoplastic damper is a rubber-steel core damper (RSCD), which consists of a high-damping rubber layer and several ductile steel bolts. The proposed column base connections prevent damage and inelastic deformations in the steel column and its base plate by allowing a rocking mechanism at the base of the column and limiting damage to easily replaceable steel bolts in the dampers. The paper discusses the design and behavior of the column base connections equipped with RSCDs. Continuum finite element models of RSCD dampers were developed and validated using experimental results. The rocking response was validated using experimental results for rocking columns with a silt damper. A total of 21 finite element models of rocking columns with RSCD were used to numerically examine the column response to combined axial loading and cyclic lateral loading. The influence of different parameters on the cyclic response of the proposed column base connections was also evaluated. These parameters are steel bolt diameter-to-length ratio (d/h), rubber thickness, column axial compressive load, number of bolts, and steel material type. The results confirmed the effectiveness of the proposed column base connection for minimizing damage to the steel column and its base plate. An optimal d/h ratio of 0.4 was found for the design of RSCDs. In addition, analytical formulas are presented to evaluate the yield and ultimate strength of the proposed column base connection, and the comparison with FEM results indicates that the presented mechanism has sufficient accuracy. [ABSTRACT FROM AUTHOR]

This paper presents an extensive numerical study on the seismic performance of steel eccentrically braced frames (EBFs) designed according to the ASCE 7-16 standard. A series of EBF building structures ranging from 2 to 12 stories located in downtown Los Angeles are designed with different yielding links, including conventional and replaceable links. The performance of the structures is investigated through nonlinear time-history analyses (NLTHAs) under a suite of 40 ground motions, selected and scaled to match the target uniform hazard spectrum. The peak deformations are first examined to assess the performance of the buildings as well as the design procedure. Residual deformations are also evaluated and critically compared with acceptable limits, to provide insight into the downtime and recovery time of EBFs after major earthquakes. Previous studies have demonstrated that the response of stable yielding systems to major earthquakes is often accompanied by significant residual deformations, and that residual drifts exceeding 0.5% can cause hindrance to the buildings occupants. In EBFs, in addition to residual drifts, residual link rotations are also relevant and expected to be more severe due to the localization of inelastic deformations in the yielding link. For replaceable modular yielding links, significant residual link rotations after major earthquakes will hinder repairs and the link replacement process, which is one of the important design objectives. The performance of EBFs is also compared with what was observed in previous studies for buckling restrained braced frames and special moment resisting frames. In the end, the results from the extensive NLTHAs are used to establish a relationship between peak drifts and peak link rotations in EBFs. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) show great potential in self-centering structures because of their appealing superelastic feature and good energy dissipation capability. The mechanical properties of SMA bars have been extensively studied over the past decades. However, the characteristics of smooth surface and poor machinability of the SMA bars, especially the widely used nickel–titanium SMAs, bring challenges to the anchorage systems in practical applications. This existing limitation is especially prominent for SMA bars designed to be used at the critical deformation locations of structural members or in seismic devices experiencing extreme working conditions. For this reason, this paper develops a novel hybrid threaded-swaged anchorage system to overcome the limitations of the current SMA mechanical splices. The uniaxial behavior of the threaded-swaged anchorage systems under different loading conditions was investigated experimentally with emphasis on the seismic application-oriented responses. Furthermore, the influence of eccentricity on the anchorage system was also considered to evaluate the SMA bars with large end rotation induced by the rocking behavior of the self-centering structures during earthquake shaking. Test results reveal that the performance of the proposed anchorage system is satisfactory with stable behavior under different loading conditions, which can provide a promising anchorage solution for SMA bars used in seismic resilient design. Moreover, a practical design method for this anchorage system is proposed for implementation in seismic applications. [ABSTRACT FROM AUTHOR]

Steel side-plate connections are reliable load path alternatives because they eliminate the fabrication challenges associated with continuity plates, especially for concrete-filled tubes (CFTs). In this paper, a new easy-to-fabricate moment connection for connecting I-beams to CFT columns using the monolithic side-plate technique is proposed. In this connection, the vertical side plates are entirely replaced by column webs to save steel material by eliminating the use of double steel plates in the connection panel zone and resolving the biaxial fabrication issues associated with the lack of welding access between the orthogonal side plates and the column. Four full-scale experimental tests consisting of two couples of relatively identical bolted and welded connections were conducted under a cyclic lateral displacement control loading protocol and a constant compressive axial load was applied to the column to evaluate the seismic performance of the connection. Furthermore, standard geometrical limitations, such as the column width and beam depth, were challenged. The results indicated that the new proposed connection exhibits sufficient stiffness and high level of ductility up to more than 4% of story drift without any strength degradation, implying that this new connection can be classified as a prequalified rigid moment connection to be used in special moment frames (SMFs) located in high seismic regions. In this paper, a monolithic side-plate connection is proposed and four full-scale specimens with oversized geometrical characteristics are experimentally investigated. The favorable results of this study show that this connection can be used as a prequalified rigid beam-to-column moment connection in intermediate and special steel moment frames consisting of box columns. The proposed easy-to-implement connection offers advantages such as decreased weight, fewer welding operations, and biaxial connection capability, which are not possible with conventional side plates. This connection is successfully implemented in an IMAX multicomplex building, with 151,676 m2 gross area and 82.32 m height. The proposed idea is applicable to any project with large box-shaped columns in high seismic regions and the achievements of this study can provide experimental support for the seismic design of these buildings. Critical factors in the connection performance are the column width and side-plate geometry, and considering other specific aspects of this connection, there is a lot of potential for further numerical and experimental investigations. Although not shown in this work, the proposed approach gives us the necessary flexibility to easily develop a biaxial moment connection, and further research is recommended in this case. [ABSTRACT FROM AUTHOR]

The 2010–2011 Canterbury earthquake sequence highlighted the vulnerability of New Zealand light-frame wood buildings that are the predominant typology in residential construction. While life-safety performance was excellent, many buildings experienced widespread cracking of internal wall linings that resulted in costly repairs and disruption. Despite the widespread use of light-frame wood construction in New Zealand, no known shake table tests have been documented for this construction typology. Additionally, New Zealand light-frame wood building performance cannot simply be inferred from international testing because New Zealand adopts a different design philosophy from those of the US and Canada by relying on gypsum sheathing as the primary lateral resisting element. To further investigate New Zealand light-frame wood building performance, this paper discusses shake table testing of a light-frame wood building specimen, constructed on the University of Canterbury unidirectional shake table using modern New Zealand design and construction approaches. The observed damages during the tests were consistent with those observed in similarly built structures that were investigated after the 2010–2011 Canterbury earthquake sequence. This paper also presents a modeling approach using the state-of-the-art software Timber3D, which was verified by simulating the shake table specimen and comparing the observed and predicted dynamic response from the test specimen and model, respectively. The Timber3D modeling approach included analysis and parameterization of screw-slip data using the Evolutionary Parameter Hysteretic Model, formulation of two-dimensional wall component models, and nonlinear time history analysis of a three-dimensional model of the shake table specimen. The model was shown to reasonably predict the displacement response of the shake table specimen and the strength degradation from cracking damage through repeated earthquakes. The modeling approach described is intended to further the development of residential building models toward the performance-based seismic design of light-frame wood buildings in New Zealand. [ABSTRACT FROM AUTHOR]

Base dual-mechanism systems that limit both shear force and overturning moment demands are being developed as a new class of seismic force–resisting systems to enhance the control of seismic demands at the base and along the height of tall buildings and to control higher-mode effects. Despite an increasing number of numerical studies that demonstrate the enhanced seismic resilience of tall buildings as a result of better-controlled shear force and overturning moment demands and reduced higher-mode effects through a variety of base dual-mechanism configurations, there are limited design methodologies for buildings with this type of seismic-resistant base system. This paper proposes a simplified method for the performance-based seismic design methodology for these base dual-mechanism systems and the structures above, which consists of (1) designing the dual base-mechanism system using a set of design charts, and (2) protecting the rest of the structure for the maximum expected seismic force demands computed using closed-form equations. The proposed method was used in this paper for the preliminary design of four example core-wall tall buildings with heights of 45, 90, 150, and 300 m. The adequacy of the proposed method was demonstrated using three-dimensional finite-element models. The analysis results were in reasonable agreement with the targeted force and displacement demands estimated using the proposed simplified method for the preliminary design of dual base-mechanism systems. [ABSTRACT FROM AUTHOR]

While numerous experimental tests have been conducted on single-story cross-laminated timber (CLT) shear walls, research addressing the drift performance of multistory CLT structures remains limited. This paper presents an experimental parameter study of the lateral performance of two-story platform-type CLT shear wall structures utilizing self-tapping screw connections. The test program consisted of six reversed cyclic tests investigating the impact of: (1) additional floor mass; (2) different angle bracket connections between floors; (3) different tension strap connections between floors; and (4) acoustic insulation layers on both sides of the first-level floor. The results showed that additional dead load increased the lateral resistance and that designing angle brackets to remain elastic limited the sliding contribution to total lateral deformations to less than 10%. The results also showed that the acoustic layer had minimal effect on the performance of the shear walls under the tested conditions. The tension straps significantly influenced the rocking performance, underscoring their importance to achieve similar story drifts in multistory CLT shear wall structures. Finally, while preceding single-story shear wall tests allowed designing the structures, hold-down uplifts on single-story tests were shown not to be representative for tension strap uplifts in multistory tests. [ABSTRACT FROM AUTHOR]

A variety of self-centering devices and structural systems have been proposed and investigated in recent years to eliminate or reduce postearthquake repair, but so far their applications are still very limited. This paper reports the seismic resilience enhancement of an irregular space structure by using friction-damped self-centering tension braces (FSTBs). First, the configuration, performance, and numerical model of FSTBs are introduced, and then a seismic design procedure for enhancing the seismic capacity of a torsional irregular structure is proposed. Taking the terminal building at the Harare Airport, a lifeline project in Zimbabwe, for example, unidirectional and three-dimensional nonlinear dynamic analyses were conducted on the building designed with and without FSTBs. The result shows that FSTBs can significantly reduce both story drifts and residual story drifts of the bottom reinforced concrete frame and displacements of the steel roof. To this end, the field assembly of FSTBs is briefly reported. The presented study provides references to the use of self-centering devices in seismic resilience upgrades of important engineering projects. [ABSTRACT FROM AUTHOR]

The composite pier, which consists of ultra-high-performance concrete (UHPC) and normal strength concrete (NSC), is a promising option for practical engineering due to its remarkable mechanical performance. However, the cyclic behavior and seismic design mechanism of the composite pier have not been thoroughly investigated. This paper aims to study the cyclic performance of the composite pier by conducting cyclic tests on 10 specimens. The thickness of the UHPC tube, strength of reinforcement, spacing of stirrups, and other parameters are considered. The crack distribution, hysteretic response, and failure modes are observed and analyzed. Results show that the composite pier exhibits good crack-control ability, large bearing capacity, and effective energy dissipation. The expansion of the inner NSC may exacerbate the buckling of the UHPC tube, thus leading to more severe seismic damage. To further investigate the composite pier, a numerical model is established to analyze the optimal thickness of the UHPC tube. The ultimate state of the composite section is taken into consideration, and the upper and lower limits of the height of the compression zone are proposed. Based on the parametric analysis, a recommended range of the UHPC tube thickness is derived. [ABSTRACT FROM AUTHOR]

Steel multitiered concentrically braced frames (MT-CBFs) not specifically detailed for seismic resistance with a response modification factor of R=3 are permitted in moderate seismic regions. Past research studies, however, have raised concerns regarding the seismic performance of MT-CBFs and CBFs designed using R=3 provisions, namely the stability of columns in MT-CBFs and connection limit states in R=3 CBFs. This paper examines the seismic response of R=3 MT-CBFs and proposes a design method to improve their seismic performance. A set of 16 prototype R=3 MT-CBFs, ranging from 8 to 20 m tall with two to five tiers and located in a moderate seismic area, was selected and designed in accordance with 2016 US design guidelines. Nonlinear response-history analyses were then performed to examine the seismic response of these frames using fiber-based numerical models. R=3 MT-CBFs designed to 2016 design guidelines are shown to experience premature fracture in brace-to-beam/column connections in a single tier, which imposes high in-plane bending demands on columns and in some cases, leads to column instability or a tier-sway mechanism. New seismic design recommendations, including requirements for intermediate struts, columns, and tier drift, are proposed. The design method aims to prevent column instability or a tier-sway mechanism and protect brace connections from excessive deformation. [ABSTRACT FROM AUTHOR]

While the use of cross-laminated timber (CLT) panels for building construction has increased over the last several decades, current standards and existing literature provide limited information regarding the design of CLT diaphragms or the prediction of their deflections when subjected to wind and strong earthquake motions. This paper presents the design and assessment of a CLT diaphragm that was part of a full-scale two-story structure subjected to shake-table testing. An analytical model is proposed for diaphragm deflection accounting for in-plane shear and bending stiffness, as well as the stiffness of various connections. Moreover, a refined numerical modeling strategy is proposed in order to consider phenomena such as panel-to-panel gap closure. Results indicate that the analytical model yields conservative results both in terms of deflections and forces when compared to the numerical model that simulates similar sources of strength and stiffness. The analytical model is suitable for the design of symmetric diaphragms with regular shapes, whereas the numerical model can also be used to model asymmetric diaphragms with irregular shapes. [ABSTRACT FROM AUTHOR]

This paper investigates the feasibility of employing timber pegged joints in modern seismic-resistant structures or for retrofitting existing structures. The behavior of timber pegged connections has been investigated for about twenty years, but seismic design aspects are not treated in existing standards. In the framework of the force-based design approach, this paper analyzes and defines seismic design aspects and rules for timber pegged connections that are easy-to-use in engineering practice. A large database (more than 350 test results) has been elaborated and the data processed with the purpose of (1) analyzing the effectiveness of the European Yield Model for evaluating the maximum strength of the connection, accounting for the particular embedding behavior due to the presence of timber peg; (2) assessing and defining the capacity design rules to design the dissipative regions (i.e., overstrength factor); and (3) defining the available ductility of the connection with identification of ductility class intervals. The obtained results proved that timber pegged joints have a good potential to be used in seismic-resistant structures. In fact, data processing identified a suitable value for the overstrength factor (useful to project the joint with the capacity design) similar to that used for steel-dowelled connections, and defined a likelihood range of ductility classes. Finally, it is highlighted that the European Yield Model can be a practical tool to calculate connection strength, provided that some modifications are included to consider peg behavior. [ABSTRACT FROM AUTHOR]

This paper presents experimental investigations on the lateral performance of cross-laminated timber (CLT) shear walls with customized self-tapping screw (STS) connections. The panel-to-base (hold-downs and shear brackets) and panel-to-panel (spline) connections were tested under quasi-static monotonic and reversed cyclic loading to derive design values of STS, which were shown to be 2.8–3.6 times higher than those calculated using the current Canadian timber design standard. Then, a total of 26 CLT shear walls, including single-, double- and triple-panel configurations, were tested, again under quasi-static monotonic and reversed cyclic loading. The shear walls consisted of five-ply, 139-mm-thick and 3-m-high CLT panels with aspect ratio of either 2∶1 or 3∶1 , and different numbers of STS in the connections. The shear wall strength and corresponding displacements increased with the number of screws in hold-downs and spline joints; further, it increased with number of connected panels and decreased as a function of aspect ratio. The data can be used for developing and calibrating numerical models to investigate the lateral responses of CLT shear walls with different configurations. [ABSTRACT FROM AUTHOR]

In response to the increasing need for sustainable construction materials, numerous innovative timber-based structural systems have been developed in the past two decades. While timber-based shear-walls are popular, moment-resisting timber frames have received less attention in recent studies. However, with the availability of ductile and resilient beam-column joints (BCJs), timber frames can now be effectively used either independently or in combination with others. This study explores the feasibility of a dual system, consisting of cross-laminated timber (CLT) balloon shear-wall and glulam moment-resisting frame (CLTW-GMRF), and investigates the potential interaction between the two systems under seismic loading. The building features ductile and energy-dissipative BCJs and hold-downs. A seismic design procedure, based on a targeted moment proportion (MP) between the two systems, is presented and applied on a 10-story building. The building is assumed to be located in Vancouver, Canada, and its seismic performance is examined using 30 ground motion records in OpenSees. The system's efficiency with respect to engineering demand parameters is studied under different wall-to-frame MP values (50%–50% and 60%–40%) and ductility-related modification factors (2, 3, and 4). The study also investigates the system's performance with two BCJs and hold-down alternatives with bilinear hysteretic and self-centering energy-dissipative responses. Given the availability of resilient connections, the result highlights that the CLTW-GMRF coupled system is a viable alternative for high-rise hybrid timber construction. Moreover, the system's performance has significantly improved by using self-centering energy-dissipative systems. This paper unveils an innovative design approach and practical application for a CLTW-GMRF dual system. This innovative system incorporates energy-dissipative components that are designed and tested in existing literature: (1) the utilization of replaceable steel damper BCJs and buckling-restrained brace hold-downs, providing high ductility with large energy-dissipative capacity; and (2) the employment of hybrid BCJs made up of post-tensioned tendons and mild steel dissipators, along with hybrid brace hold-downs made up of pretensioned tendons and friction surfaces, which reduce residual deformations following seismic events. Utilizing these systems, the research introduces a versatile seismic design method congruent with existing codes and design standards, while offering flexibility through adjustable wall-to-frame moment proportions. The research also underlines the need for careful consideration of the interaction within the timber wall-frame systems. The implications are substantial amidst the growing trend of high-rise timber construction, aiming to fully exploit the potential of CLT and Glulam frames. Moreover, the research has the potential to serve as an essential resource for engineers aiming to optimize the sustainability and resilience of timber structures, particularly in seismic-prone regions. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results of two welded unreinforced flange-welded web (WUF-W) beam-to-column connections that defy the current design paradigm of prequalified welded connections. The proposed WUF-W connections feature customized beveled backing bars that are intentionally left in place after the completion of the beam flange-to-column face complete joint penetration welds. The connection design aims at a stable hysteretic response by exploiting the beneficial aspects of appreciable panel zone shear yielding (i.e., inelastic shear distortions of at least 15γy , where γy is the panel zone shear distortion at yield), by considering a shear strength-to-demand ratio of 0.8. To prevent divot fracture in the column, minimum through-thickness toughness requirements were imposed for the steel column material. The experimental results suggest that the proposed WUF-W connections achieve a stable hysteretic response up until lateral drift demands of at least 7% rad, while a non-softening response was assured up to 9% rad. The beveled backing bars minimize the associated fracture potential near the beam web centerline, which is a primary concern in prequalified field welded moment connections when conventional weld backing bars are employed. The tests suggest that, under a symmetric cyclic loading protocol, local buckling near the steel beams is prevented up until a lateral drift demand of 6% rad, which is an important finding from structural repairability and stability standpoints. The ultimate failure modes of the welded connections, which are attributable to ductile crack initiation and propagation, are consistent regardless of the employed lateral loading histories, which involved standard symmetric cyclic and collapse-consistent loading protocols. The implications for the seismic design of steel moment resisting frames (MRFs) and the limitations of the present work are discussed. [ABSTRACT FROM AUTHOR]

Mixed multiple seismic systems (MMSSs) are ideally suited for sustainable seismic design (SSD). MMSSs are combinations of two or more different earthquake-resisting structures (ERSs) that provide lateral support for gravity frameworks. Same-system combinations have been demonstrated to not be suitable for SSD. Regardless of the carbon footprint reduction, unless a structure has been designed for seismic sustainability it would be disposable with greater harm to the environment. Here, design means planning for both seismic resistance as well as post-earthquake realignment and repair (PERR). Earthquakes are random, natural, and dynamic events, whereas PERR is a deliberate, manual, and static process. In SSD the practicality of PERR is as important as the relevance of the theoretical assumptions. In SSD the non-lateral-resisting items are designed not to partake in seismic resistance, nor hinder the realignment process. Additionally, efforts are made to mitigate the P -delta effects that undermine the global strength of the system and oppose the recentering effort. The purpose of this paper is to identify and remedy design flaws and physical issues that prevent MMSSs from achieving seismic sustainability as cost-effectively as possible. Two newly developed technologies, the ladder moment frame (LMF), and the fail-safe (FS) system, as well as a capacity distribution rule together with six simple axioms are introduced. Brief descriptions of LMF and FS are presented in the text. Any structure designed to survive earthquakes is expected to either remain elastic and stable or be capable of post-earthquake realignment and repairs. Sustainable seismic design is a new field of research that promises improved environmental conditions and innovative developments in structural engineering. Regardless of the carbon footprint reduction, unless a structure has been designed for the purpose, it would be disposable with greater harm to the environment. Here, design implies planning for seismic resistance as well as post-earthquake realignment and repairs. The difference between conventional and sustainable seismic design is in the modes of behavior during and after the event. In conventional seismic design, the object is to satisfy code-specified requirements; in sustainable seismic design, the post-earthquake attributes of the system are as important as those during the event. The paper shows that seismic sustainability can be achieved without resorting to untenable costs and technologies. In light of current findings, it is suggested to include post-earthquake realignment and repairs in seismic design guidelines for new construction. [ABSTRACT FROM AUTHOR]

Composite plate shear walls/concrete-filled (C-PSW/CFs), also known as SpeedCore systems, are a relatively new structural member in American codes and standards. Prior research has focused primarily on C-PSW/CF walls with either flange/closure plates or filled composite members as boundary elements. Walls without boundary elements have also been studied, but they are no longer permitted by the American Institute of Steel Construction (AISC 341-22). The reason is that composite walls without boundary elements do not provide adequate ductility for seismic design. This paper presents the results of experimental and numerical studies conducted to evaluate the cyclic lateral load behavior of C-PSW/CFs using hot-rolled structural steel members as boundary elements. The steel web plates of the C-PSW/CF specimens were connected to each other using threaded tie bars with double nut connections. Composite interaction between the steel and concrete infill was achieved using the tie bars and additional shear studs welded to the boundary elements. The composite walls were embedded and anchored to reinforced concrete foundation blocks using welded deformed bar anchors. The experimental investigations focused on the cyclic lateral load-drift responses including test observations and limit states, moment-rotation response of the plastic hinge and the section moment-curvature relationship, overall lateral stiffness, strength, and displacement ductility. The experimental results show that the specimens exceeded their nominal flexural capacities calculated using the plastic stress distribution method or fiber-based section modeling using measured material properties. The specimens had plastic hinge rotation capacity greater than 0.028 rad. and displacement ductility ratio greater than 5.2. Detailed 3D nonlinear inelastic finite element models and simpler fiber-based macro models of the tested specimens were developed and benchmarked using experimental results. The detailed 3D finite element models can reasonably simulate the global and local behavior of the specimens, and are recommended for conducting further parametric studies of composite wall design details. Simpler fiber-based macro models can efficiently simulate the cyclic lateral load behavior of the specimens, and are recommended for modeling C-PSW/CFs while simulating the behavior of multi-story building structures. [ABSTRACT FROM AUTHOR]

This paper describes the state of the art of structural steel reuse in Japan. A significant part of the material is taken from a document titled the Architectural Institute of Japan (AIJ) Recommendations for Sustainable Steel Building Construction (Draft) available only in the Japanese language. The motivations for and potential benefits of steel reuse are examined. The affinity between seismic design requirements and steel reuse is highlighted through a concept known as "damage-control" design. Some technologies for disassembly are introduced. The historical development and changes in Japanese structural steel are summarized, followed by a discussion on reusability of historical steel reclaimed from existing buildings. Reuse projects whose details are known to the authors are listed. The heart of the paper is a design procedure that specifies the structural engineer's role and involvement in planning, material procurement, and executing a steel reuse project. The discussion is concluded by six directions that should be pursued to make steel reuse a widely accepted reality in Japan. Among those directions are research needs to establish a procedure to quantify the remaining structural performance of reclaimed steel considering possible exposure to earthquakes, establish connections that allow for easy disassembly, and introduce modularized structural systems. High seismicity and the general practice to adopt full moment frames pose unique challenges for steel reuse in Japan. [ABSTRACT FROM AUTHOR]

This paper proposes damage index–based limit-state criteria for seismic design of midrise cold-formed steel (CFS) buildings instead of the drift-based ones, and the Park-Ang damage model was used to calculate the damage indexes. Two 5-story CFS buildings with different wall configurations were tested, and a test-validated numerical model was developed. An incremental dynamic analysis was conducted on a typical midrise CFS building to obtain the degradation parameter β of different CFS walls. The damage indexes computed from numerical analyses were compared with the damage indexes estimated from test observations and the proposed damage index–based limit-state criteria. The results showed that the calculated degradation parameter as well as the proposed damage index–based limit-state criteria are effective for seismic damage assessment and damage level classification of midrise CFS buildings according to the validations by shaking-table tests on two CFS buildings. The Park-Ang damage index used in this paper and the proposed limit-state criteria could be used for performance-based seismic design of midrise CFS buildings. [ABSTRACT FROM AUTHOR]

Steel eccentrically braced frames (EBFs) combine the advantages of both moment-resisting frames and concentrically braced frames and provide an attractive seismic design solution. Shear-critical replaceable links were developed about a decade ago to improve the performance, design process, construction, and postearthquake repair process in EBFs. However, replaceable shear links are still susceptible to the commonly observed limit states in EBF links such as web fracture close to web stiffeners, local buckling, and lateral torsional buckling. This paper presents the experimental validation of a new generation of optimized cast steel replaceable yielding links for use in EBFs, which address the shortcomings of conventional and fabricated replaceable links. The performance of the proposed cast steel links is investigated through nine large-scale component-level and system-level experiments, covering a range of link sizes and loading conditions, while also studying the impact of other phenomena influencing the response such as the presence of axial load, the level of axial restraint in the links and the presence of a concrete slab. The tested series of cast links demonstrated enhanced ductility levels and low-cycle fatigue life when compared to fabricated links, achieving up to 0.21 radians of link rotation under the AISC protocol used for the qualification of EBF links. [ABSTRACT FROM AUTHOR]

This paper presents the analytical formulation and computational implementation of a conceptual probabilistic performance-based seismic design (PBSD) framework for ordinary standard bridge (OSB) structures. An updated probabilistic performance-based earthquake engineering (PBEE) assessment methodology is used for the parametric performance assessment of four distinct OSBs in California to investigate the effects of varying key structural design parameters over a primary design parameter space on risk-based structural performance measures. The dire need for a systematic PBSD framework for OSBs is illustrated given the significant variability in risk-based performance levels exhibited by these traditionally designed testbed OSBs. A PBSD methodology involving the design of the bridge piers is proposed wherein a risk-based feasible design domain in the primary design parameter space is identified which facilitates the risk-informed design/decision making process in the face of uncertainty. Sensitivities of risk-based feasible design domains compared with other (secondary) design variables and with the method employed for damage hazard assessment are investigated. [ABSTRACT FROM AUTHOR]

Self-centering piston-based braced frames (SC-PBBFs) are such structural assemblies that can withstand a severe earthquake through passive control. The self-centering motion of the bracing system curtails the seismic permanent damage of a building, thereby considerably mitigating postearthquake repair costs and downtime. This paper proposes a novel hybrid self-centering piston-based bracing (SC-PBB) equipped with friction springs (FS) and superelastic shape-memory alloy (SMA) bars. Analytical formulas are presented for rapid analysis and preliminary seismic design of the SC-PBBFs fitted with SC-PBBs. The general mechanics of the proposed archetypes confirms their symmetric self-centering behavior. To validate the proposed design procedure, a set of SC-PBBFs fitted with tension-only SMA bars and precompressed FS is examined under far-field ground motions. Effects of prestressing of components and earthquake types (crustal, subcrustal, and subduction) are quantified and compared with the responses of buckling-restrained braced frames (BRBFs). The analysis outcomes revealed the effectiveness of the proposed hybrid SC-PBBF subjected to design-level earthquakes. [ABSTRACT FROM AUTHOR]

In this paper, the seismic design factors for uncoupled composite plate shear walls/concrete filled (C-PSW/CF), a.k.a. SpeedCore, are verified by conducting a study using FEMA methodology. These are the seismic response modification factor, R, the deflection amplification factor, Cd, and the overstrength factor, Ωo; and their values for C-PSW/CF are specified as 6.5, 5.5, and 2.5, respectively. A study was needed, as these factors for uncoupled C-PSW/CFs, included in ASCE 7 since as far back as its 2000 edition, were chosen solely based on the seismic performance of similar structural systems and engineering judgment of the committee members. For this study, four archetypes with planar walls and three archetypes with C-shaped C-PSW/CF walls were chosen. Two different damage measures (DM) were chosen for this study; namely, 3% and 5% maximum interstory drifts. Based on FEMA methodology, all archetypes satisfied the specified performance requirement considering a "good" rating for total system collapse uncertainty (βTOT). [ABSTRACT FROM AUTHOR]

Links in eccentrically braced frames (EBFs) are designed with transverse web stiffeners to achieve the desired seismic performance targets established in current design standards. Prior studies have suggested that stiffener spacing requirements in the standards may be conservative. This paper proposes new stiffener spacing design requirements for short EBF links. The proposed limits were established on the basis of a methodology that combines a numerical solution of the classical problem of inelastic plate buckling of a thick plate under shear thrusts along with comparisons with available experimental data. The resultant design equation was verified through complementary continuum finite-element simulations of 18 wide-flange short links under symmetric cyclic loading. The finite-element simulations suggested that the proposed design equation reduce the stiffener requirements by about 35%, on average, relative to the current stiffener spacing requirements for short EBF links. Limitations and suggestions of future work are discussed. [ABSTRACT FROM AUTHOR]

Composite plate shear walls–concrete-filled (C-PSW/CF) are a new and innovative lateral force–resisting system intended for high-rise buildings. High-rise building applications of this system are particularly efficient in the coupled wall configuration, in which the walls are C-PSW/CF and the coupling beams are concrete filled steel box sections. This paper presents a capacity design principle for the seismic design of coupled composite plate shear wall–concrete filled (CC-PSW/CF) systems. The capacity design principle implements a strong wall–weak coupling beam approach, in which flexural yielding occurs in the coupling beams before flexural yielding at the base of walls. The coupling beams are sized to resist the calculated seismic lateral force level. The composite walls are sized to resist an amplified seismic lateral force corresponding to the overall plastic mechanism for the structure, while accounting for the capacity-limited forces from the coupling beams and the coupling action between the walls. The paper summarizes the recommendations and requirements for appropriate sizing of the composite coupling beams and walls. These recommendations were used along with the capacity design principle to design four example (8–22-story) structures and evaluate their seismic behavior. The structures were modeled using benchmarked finite-element models and fiber-based models that accounted for the various limit states, including steel yielding, local buckling, fracture, concrete crushing, confinement, and tension cracking. The numerical models were analyzed for monotonic pushover loading and scaled seismic ground motions. The structural responses from the nonlinear pushover analysis and the nonlinear time history analyses were in accordance with the capacity limited design philosophy, thus confirming its efficacy. [ABSTRACT FROM AUTHOR]

Post-tensioned (PT) timber technology, also referred to as Pres-Lam (prestressed laminated timber) provides a low damage seismic design solution. So far PT timber research and practical implementation have focused on moment resisting frames, planar shear walls and coupled planar shear wall—or column-wall-column—systems and their analytical prediction models were adapted and extended from precast concrete to account for the unique characteristics of engineered timber. Following a recent experimental study on a PT cross-laminated timber (CLT) C-shaped core-wall system aiming to enhance lateral strength and stiffness, this paper presents an analytical framework/model to capture three unique kinematic rocking mechanisms for a PT C-shaped CLT core-wall system connected primarily with self-tapping screws. Depending on the relative stiffness of the screwed connections to the PT and the energy dissipaters, the model considers different kinematic responses, and that a staged kinematic response could occur at different imposed core-wall base connection rotations. It also accounts for the material inhomogeneity of CLT with nonedge glued lamella and implements a nonlinear spring model for the screwed connections calibrated from component testing and expected elastic core-wall deformations. The study showed that, for the given specimen configurations presented, the compressive flange wall could be neglected for a PT C-shaped CLT core wall. The analytical model was verified against three large-scale 8.6 m high PT C-shaped core-wall experimental tests and the model prediction error was within 10%. The analytical model was limited to capturing the envelope (push-over) curve of a four wall PT C-shaped CLT core-wall system. [ABSTRACT FROM AUTHOR]

The reduced damage and residual deformations of rocking systems make them efficient for designing resilient buildings for earthquakes. This paper presents a design approach for multiple-rocking coupled self-centering concentrically braced frames (SC-CBFs) with linear fluid viscous dampers (FVDs) utilizing an efficient gradient-based optimization procedure. The optimization problem is formulated such that the framing system, the post-tensioning layout, and the location of the rocking sections are simultaneously designed with the FVDs. The constraints of the optimization problem are formulated following performance-based seismic design. These constraints are evaluated based on results obtained from nonlinear time history analyses of the system when subjected to an ensemble of ground motion records. For the first time, a design method suitable for irregular buildings with multiple-rocking coupled SC-CBFs is proposed. A nine-story irregular building was designed using the proposed method. The results show that an efficient design can be achieved with reasonable computational effort. In addition, the results show that the design of these buildings is not intuitive. A multiple-rocking solution was obtained to reduce force demands in the framing elements. [ABSTRACT FROM AUTHOR]

Steel bar corrosion is one of the most common causes of structural performance degradation for reinforced concrete (RC) columns subjected to extreme loads such as earthquakes. Due to the different characteristics of corrosion effects, a comprehensive and efficient finite element (FE) modeling approach is necessary for the performance assessment of corroded RC columns. To this end, this study provides an effective FE modeling approach using a recently developed geometrically nonlinear fiber-based frame element that considers bond-slip, allowing for explicit representation of corrosion-affected bonding. This aspect necessitates the use of an explicit material model for corroded bond-slip and its associated corroded properties. Since the existing models of corroded bonding properties in the literature were developed based on the highly scattered and limited experimental data, this study develops a new probabilistic model for corroded bonding properties based on more experimental data compiled from the literature and quantifies the prevailing uncertainties. To facilitate its use for modeling corroded RC structures, a cyclic corroded bond-slip model in an open-source FE software framework is implemented. In this paper, the FE modeling approach is first used to model two corroded RC columns tested in the literature, with comparison to the conventional modeling approach (i.e., assuming perfect bonding). The influence of corroded bonding on the static and dynamic behaviors of RC columns is further explored deterministically. Furthermore, the impact of uncertainty in corroded bonding properties on the static and dynamic behavior simulations of RC columns is examined. This work is concluded that (1) the FE modeling approach provided for corroded RC columns proves to be effective in capturing corrosion effects; and (2) corroded bonding plays an important role in simulating the behavior of corroded RC columns, and thus cannot be neglected. This is particularly true considering its associated uncertainty and its impact on the performance assessment of RC columns under severe corrosion conditions. [ABSTRACT FROM AUTHOR]

Stiffness modifiers are used in linear structural analysis programs to recognize the low-strain amplitude nonlinear material stress–strain response and support the design of reinforced concrete structures. For example, stiffness modifiers are used to account for the reduction in stiffness that results mainly from crack development and propagation, bar bond slip between cracks, and bar bond slip of the longitudinal reinforcement developed beyond the column ends. This paper presents a primarily mechanistic model to compute the stiffness modifiers for reinforced concrete rectangular columns to support the seismic design of reinforced concrete structures. The model accounts for five modes of deformation found in columns and is calibrated against a database of test results reported in the literature on 38 large-section columns that exhibited ductile response. The paper also describes a simplified equation for use in seismic design. The simplified equation was calibrated through an extensive parametric analysis of the model. The mean, median and coefficient of variation of the ratios of the stiffness modifiers computed from the recorded response of test columns and the model output were 1.02, 1.00, and 0.18, respectively, and those calculated by the simplified equation for the same ratios were 0.95, 0.98, and 0.18, respectively. [ABSTRACT FROM AUTHOR]

Complementing a companion paper that summarizes the building global response and physical damage of a midrise cold-formed steel (CFS) framed building during an earthquake and postearthquake fire test program, this paper focuses on understanding the seismic behavior of the shear walls utilized in the building system during this test program. In contrast to shear walls tested in an isolated configuration, the shear walls within the full-scale test building were constructed and tested under real-world kinematic constraints and dynamic loading environments. The shear walls located at various planar and vertical locations of the test building were instrumented with a dense array of analog sensors to monitor the shear wall local responses. In this study, the shear wall local responses are correlated with the global responses of the building to advance understanding regarding the behavioral characteristics of individual shear walls and in particular the interactions of the shear walls as part of the lateral-load-resisting system. Important seismic design parameters are inferred from the measured building response using a parameter optimization strategy. Their implications associated with the seismic design of CFS wall-framed structural systems are discussed in relation to code provisions and design guidelines. [ABSTRACT FROM AUTHOR]

To advance understanding of the multihazard performance of midrise cold-formed steel (CFS) construction, a unique multidisciplinary experimental program was conducted on the Large High-Performance Outdoor Shake Table (LHPOST) at the University of California, San Diego (UCSD). The centerpiece of this project involved earthquake and live fire testing of a full-scale 6-story CFS wall braced building. Initially, the building was subjected to seven earthquake tests of increasing motion intensity, sequentially targeting service, design, and maximum credible earthquake (MCE) demands. Subsequently, live fire tests were conducted on the earthquake-damaged building at two select floors. Finally, for the first time, the test building was subjected to two postfire earthquake tests, including a low-amplitude aftershock and an extreme near-fault target MCE-scaled motion. In addition, low-amplitude white noise and ambient vibration data were collected during construction and seismic testing phases to support identification of the dynamic state of the building system. This paper offers an overview of this unique multihazard test program and presents the system-level structural responses and physical damage features of the test building throughout the earthquake-fire-earthquake test phases, whereas the component-level seismic behavior of the shear walls and seismic design implications of CFS-framed building systems are discussed in a companion paper. [ABSTRACT FROM AUTHOR]

Nonstructural components typically are not designed for seismic loads, yet their behavior can affect the postearthquake building functionality significantly. Nonstructural damage occurs at low to moderate seismic intensities, heavily contributing to downtime and overall financial loss. Moreover, the failure of these elements can represent a potential life-safety threat for occupants and pedestrians. Due to increased awareness of these issues, in recent decades substantial research efforts have been dedicated to the study of nonstructural seismic behavior. Focusing on architectural elements (facades, partitions, and ceilings), this paper provides a state-of-the-art review of fragility functions. Seismic damage states were described and literature data were collected to build fragility domains for different nonstructural archetypes. Furthermore, references to innovative low-damage technologies are provided, and traditional (i.e., construction practice) systems were compared with low-damage components in terms of fragility. A fragility-based direct design approach is suggested based on the state-of-the-art review: nonstructural details could be designed, manufactured, or selected specifically to target desired tailored fragility curves representing targeted (multi)performance levels. [ABSTRACT FROM AUTHOR]

Concentrically braced frames (CBFs) are widely used to resist lateral loads in buildings because they are relatively simple and economical to design and construct. In tall, single-story construction, it is often practical to replace a single brace or brace pair within the story with multiple bracing panels or tiers. This leads to a multitiered braced frame (MT-BF), which in contrast to the more traditional multistory braced frame (MS-BF) lacks intermediate out-of-plane supports between the ground and the roof levels. While the primary seismic energy dissipation mechanism in both systems is through brace inelastic axial response, in MT-BFs, the majority of the mass is concentrated at the roof level, which has important implications for seismic design and response. The unique conditions that arise in the inelastic response of a MT-BF during a seismic event are known to cause drift concentration and increase the propensity for column instability due to combined axial and flexural demands. This study employs detailed models that consider geometric and material nonlinearity to rigorously quantify the behavioral differences between the two system types. For both multistory and multitiered frames, the models can capture column buckling and story-sway mechanisms. Results from nonlinear static pushover and response history analyses for two pairs of frames are used to evaluate the demands that develop during an earthquake event, and new insights are provided on the effect of column orientation and bracing conditions. The paper shows that the potential for column buckling is not exclusive to MT-BFs; considerable in-plane flexural demands, combined with axial loads, are shown to cause in-span plastic hinges that can also lead to buckling of MS-BF columns. Out-of-plane moment demands are larger in MT-BFs due to the lack of restraint at the tier levels. Drift distribution tends to be improved in MS-BFs compared to the corresponding MT-BFs, but the potential for brace fracture under maximum considered earthquake seismic input remains high regardless of system configuration. [ABSTRACT FROM AUTHOR]

To overcome the shortcomings of traditional shear walls, structure systems have been proposed and investigated. One such structure system is a steel-reinforced concrete shear wall, which has certain desirable properties such as good load-bearing capacity, stiffness, and seismic performance. This paper proposes an M-section cold-formed thin-walled steel reinforced concrete (MCTSR) shear wall, which uses M-section cold-formed thin-walled steel to function as reinforcements. Six specimens with different permanent formwork types, axial compression ratios, reinforcement diameters, and other parameters were tested under cyclic loading to investigate seismic performance. The results demonstrate that various types of permanent formwork, including cement fibrolite plate, metal lathing, and polystyrene board can meet the requirement of related seismic design codes, construction demand, and assembly requirements, and have no obvious impact on the ultimate load-bearing capacity, lateral stiffness, and stiffness degradation rate. However, it changes the energy dissipation capacity and ductility, which are two important indexes to evaluate seismic performance in engineering practice. The failure mechanism and the influence of axial compression ratio, reinforcement diameter, and space between reinforcements are discussed. The shear-strength equations proposed by various countries' or regions' codes were analyzed, which can be used as a reference for related engineers and designers. Finite-element models for MCTSR shear walls were established for further investigation. [ABSTRACT FROM AUTHOR]

In this paper, the shaking table tests and finite element analyses were conducted on the traditional thermal power plant main building and the thermal power plant main building with BRBs, respectively. The differences in torsional resistance between the two structural systems were studied, and the suppression effect on the displacement field distortion of the plane consisting of crane and tracks through adding BRBs in the thermal power plant main building was discussed. The study shows that after adopting a buckling-restrained brace in a thermal power plant main building, the damage and torsional response of the structure under an earthquake can be reduced, the occurrence of inelastic torsion can be effectively blocked, and the translation-torsion coupling effect can be reduced. At the same time, it can reduce the distortion amplitude of the displacement field of the plane consisting of crane and tracks and play a key role in improving the reliability of roof truss, crane, coal bucket, and low-ductility connectors, and it also facilitates the realization of performance-based seismic design. [ABSTRACT FROM AUTHOR]

The ability to conduct accurate regional seismic risk assessments is key to informing a risk-reduction policy and fostering community resilience. This paper presents a machine learning-based framework to predict a building's postearthquake damage state using structural properties and ground motion intensity measures as model inputs. The machine learning techniques assessed, namely, logistic regression, k-nearest neighbors, decision tree, random forest, AdaBoost, and gradient boosting, are trained using a dataset of nonlinear response history analysis results from 36 detailed structural models of modern reinforced concrete shear wall buildings ranging from four to 24 stories and subjected to approximately 500 ground motion records with a range of shaking intensities. The results indicate that the gradient boosting classifier is the most efficient algorithm by achieving a prediction success (F1-score) of 87%. The proposed framework also leverages synthetic data samples to support the prediction of severe damage state instances, that is, collapse. The percentage of observed collapse cases correctly classified by the gradient boosting algorithm is increased from 76% to 93% when synthetic data are also used for training. The framework is implemented in a portfolio of reinforced concrete shear wall buildings across the Metro Seattle region to quantify earthquake-induced damage and collapse risk. The framework shows great potential for enhancing regional seismic risk assessments by leveraging datasets of detailed nonlinear response history analysis results. [ABSTRACT FROM AUTHOR]

This paper proposes a novel, cold-formed portal framing system that comprises tapered box members formed from two cold-formed nested channel sections. The proposed method possesses structural and nonstructural advantages, such as improved seismic performance, enhanced building hygiene through bird and dust resistance, further corrosion resistance, and aesthetic improvement, as a result of fly bracing removal. The novelty of the box member lies in the tapering ability of the section, leading to material and paint savings. To examine the failure mechanisms and structural performance of the tapered box portal frame and to investigate the adequacy of the design method, two full-scale portal frames with an 18.16-m span were built and tested to failure under two common loading scenarios. The first was lateral cyclic loading into the inelastic range in conjunction with a vertically acting permanent load. The possibility of ductile plastic hinge formation in a severe earthquake was investigated using lateral cyclic testing. The second was vertical loading to failure. A novel economic loading setup was used to apply the gravity load on the frame. For the seismic design of this section type, slenderness limits are proposed for seismic applications along with the design ductility. A rotational stiffness value for a nominally pinned portal frame column base was also suggested in this study. [ABSTRACT FROM AUTHOR]

The use of prequalified welded unreinforced flange-welded web (WUF-W) beam-to-column connections in capacity-designed steel moment-resisting frames necessitates the removal of the weld backing bar at the bottom beam flange-to-column flange groove welded portion. Weld root back gouging and fillet weld reinforcement is also necessary to minimize the fracture potential at this location. This paper revisits the current detailing of WUF-W connections in order to propose simplifications in their fabrication process by intentionally keeping a customized beveled backing bar in place without impairing the connection's ductility under seismic loading. The analysis relies on traditional fracture mechanics applied in three-dimensional continuum finite element models. The modeling approach is validated with welded unreinforced flange-bolted web (WUF-B) pre-Northridge connection tests. The results suggest that field-welded connections with the proposed beveled backing bar reach lateral drift demands of at least 4%–6% rads even when flange groove welds feature a low-toughness E70T-4 weld electrode, which was typical in pre-Northridge WUF-B connections. Fillet weld reinforced backing bars provide inferior connection ductility compared to the proposed beveled backing bar. The simulation results from a series of prequalified WUF-W connections that respect the current seismic design and fabrication requirements, indicate that when the beveled backing bar configuration is intentionally left in place after completing the complete joint penetration groove welds, WUF-W connections can sustain lateral drift demands of at least 6% rads prior to fracture regardless of the panel zone strength, the steel beam depth, and the flange thickness of the respective beam and column. Limitations as well as suggestions for future work are also discussed. [ABSTRACT FROM AUTHOR]

This data paper reviews the experimental research on fully restrained beam-to-column connections for steel moment-resisting frames (MRFs) over the last 50 years worldwide and presents an experimental database consisting of 100 tests with an emphasis on those exhibiting inelastic panel zone behavior. The collected data, which is organized in a consistent format, includes full digitized histories of the local panel zone shear force–shear distortion as well as the global force–displacement hysteretic diagrams of each experiment. In most cases the original data was only available in paper format. The gathered dataset suggests that the existing panel zone models that are currently used for the seismic design of steel MRFs deviate, in some cases considerably, from the measured response quantities of an actual panel zone. These involve the panel zone stiffness and shear resistance at selected inelastic shear distortions of interest to the engineering profession. The assembled inelastic panel zone database provides ranges in which post-Northridge beam-to-column connections, which exhibit considerable inelastic deformations within the panel zone web, may achieve lateral drift demands larger than 4% without experiencing premature fracture. The assembled dataset constitutes an important source for validation of continuum finite-element models that could aid the simulation-based engineering design of steel MRF beam-to-column connections designed with a balanced design approach. The database is made available to the engineering and research communities through a publicly available data repository. [ABSTRACT FROM AUTHOR]

This paper presents a risk-based optimal design procedure for seismic retrofitting of existing RC buildings with dissipative bracing systems. The procedure extended to retrofit interventions an existing method for probabilistic displacement-based design of new RC buildings. Performance objectives for multiple performance levels or limit states were formulated in terms of maximum mean annual frequency of exceedance (MAF) modeled with closed-form equations based on a second-order approximation of the hazard curve. Retrofit design variables included the characteristics of the braces, conceived as a series arrangement of an elastoplastic dissipative device and a steel truss. To make the gradient-based optimization procedure suitable for practical application, the response under seismic loading was obtained by means of response spectrum analyses for multiple hazard levels, which in turn required the use of linear equivalent models to describe the inelastic behavior of both braces and RC members. Specific member-level expressions for secant stiffness and dissipated energy were used for this purpose. A multistory low-code, height-irregular RC frame taken from an existing building was adopted as a case study. Results in terms of brace properties, interstory drift ratio profiles for each hazard level, and MAF of exceedance were shown and discussed. Finally, the procedure was validated computing MAF of exceedance by means of inelastic response-history analyses carried out within a multistripe analysis scheme, with natural ground motion records selected to match hazard-consistent conditional spectra. [ABSTRACT FROM AUTHOR]

This paper presents full-scale experiments and computational analyses on exposed column–base plate connections with ductile anchors. The aim is to examine the seismic performance of these connections for their prospective use as weak bases, wherein steel moment frames are designed to concentrate inelastic rotations in the base connections rather than in the connected columns. The connections feature upset thread anchor rods in which the threads are milled to a smooth shank, providing a designated stretch length over which inelastic deformations may be concentrated. The shank is frictionally isolated from the footing using polyethylene tape. The four full-scale experiments investigate the effects of axial force, rod diameter, and rod material grade. The test specimens withstand (without anchor rod failure) the application of two Applied Technology Council–the Joint Venture partners of the Structural Engineers Association of California, the Applied Technology Council, and the Consortium of Universities for Research in Earthquake Engineering (ATC-SAC) protocols applied consecutively (each to drift amplitudes of 5%), followed by additional cycles to 6.5% drift amplitude. Complementary line element–based and continuum finite-element simulations are conducted to examine to what extent the experimentally observed response may be generalized to untested configurations. Implications for design are summarized, along with the limitations of the study. [ABSTRACT FROM AUTHOR]

When facing multiple, competing, objectives such as those encountered in resilience-based design of buildings (e.g., cost reduction versus functionality preservation), there is no single design that can be declared objectively better than the rest. Multiobjective optimization (MOO) methods can instead be used to identify a group of design alternatives that represent the optimal trade-offs between competing objectives. In doing so, however, MOO relies on performance evaluation for a large number of design alternatives, representing a problem for performance-based building seismic design, which typically involves computationally intensive and time-consuming nonlinear analyses of building models subjected to suites of ground motion records. Furthermore, only minimal guidance exists for the post-MOO selection of a final design from the optimal set, further impeding its adoption in design of buildings. This paper addresses these issues through use of simplified structural models and methods applied within a MOO methodology, coupled with a newly adapted post-Pareto pruning approach to narrow down the optimal design set to a manageable-sized group of final design alternatives. The methodology was applied to optimize the design of a 7-story reinforced concrete moment frame office building in San Francisco. [ABSTRACT FROM AUTHOR]

Beam–column joints in concrete buildings are critical for structural integrity under earthquake loading. Thus, accurate beam–column joint nonlinear models are important in seismic assessment and design of buildings. Most joint models in the literature are deterministic; the majority of which either are based on a small data set or do not distinguish failure modes and types of joints. This paper presents a data-driven probabilistic nonlinear model for concrete beam–column joints with transverse reinforcement. The model is based on multilinear regression using a newly developed database of 395 reinforced (confined) joints. Based on this database, current US seismic assessment provisions for beam–column joints were found to be conservative and have inconsistent levels of probability of exceedance for various nonlinear modeling parameters. The proposed probabilistic model unifies the level of probability of exceedance at 50%, a level that is consistent with the recently updated nonlinear beam and column provisions to avoid the bias in nonlinear assessment procedures. The proposed model exhibited good correlation with the test database, validation data sets, and cyclic backbones curves. Improved performance-based seismic design accuracy and economy for ductile concrete frames may result if current seismic assessment standards are updated based on the proposed model. [ABSTRACT FROM AUTHOR]

This paper proposes a stochastic life-cycle assessment (LCA) as a general stochastic formulation to quantify the environmental impact of an engineering system. The assessment is performed in terms of embodied energy, energy consumption, and the carbon footprint during the service life of the system. At the same time, its ability to resist a hazard is considered. The proposed formulation is general and takes into account the effects of shocks (robustness) and gradual deterioration (durability), assessing the greenhouse gas (GHG) emissions due to repair or reconstruction after an undesired event. The formulation is used in an example of a 4-story reinforced concrete (RC) office building, whose construction site is relevantly seismic. Two different seismic design levels are compared. [ABSTRACT FROM AUTHOR]

This study developed a special energy dissipation X-bracing for cold-formed steel (CFS) shear walls to improve the ductility of the corrugated steel sheathing. In previous research, CFS shear walls with corrugated sheathing demonstrated poor ductility under cyclic loading. The paper presents a potential solution by adding a special energy dissipation bracing (EDB) to improve the ductility of the corrugated sheet–sheathed shear walls. The EDB can be tuned according to the CFS shear wall base performance to achieve the highest postpeak deflection capacity, thereby significantly improving the seismic ductility. To prove the concept and analyze the feasibility of the new EDB, a test program of nine full-scale shear walls was conducted. The experimental results showed that with the tuned EDB, the corrugated steel sheet–sheathed shear walls had improved ductility with no considerable reduction in the initial stiffness and shear strength. Installing the proposed EDB can be an efficient approach to enhance the seismic performance of CFS-framed shear walls. Details of the test program and discussion are presented. [ABSTRACT FROM AUTHOR]

This paper presents experimental investigations on the seismic behavior of cross laminated timber (CLT) shear walls in a balloon frame configuration with various ledger assemblies attached at midheight. The tested system consisted of two seven-ply 191-mm-thick CLT panels with generic hold-downs, steel angle brackets, plywood surface splines, and nails as fasteners. A 2-story system was tested with a panel aspect ratio of 3∶1 with different steel and wood ledgers under monotonic and quasistatic reversed cyclic loading. Three ledgers were subsequently tested under vertical quasistatic monotonic loading to determine their remaining load-carrying capacity. The tests showed that the shear wall displacement was due to the rocking of the wall panels, which themselves behaved as rigid bodies with negligible in-plane deformations. When compared to the monotonic tests, the strength in reversed cyclic tests was up to 21% lower. The ledger did not impede the desired rocking behavior of the wall, nor did the rocking of the wall reduce the remaining gravity load-carrying capacity of the ledgers by more than 7%. Balloon-framed CLT shear walls can be detailed and designed using the Canadian standard specifications for platform-type construction. [ABSTRACT FROM AUTHOR]

In this paper, the seismic performance and resilience of a 15-story variable-damping self-centering braced frame (VD–SCBF) were analyzed. The interstory drift ratios (IDRs) of the VD–SCBF are similar to those of the buckling-restrained braced frame, but are lower than the prepressed self-centering braced frame (PS–SCBF). The residual deformation ratios (RDRs) of the VD–SCBF are reduced, and its story acceleration ratios are smaller than the PS–SCBF. Under near-fault earthquakes, the higher-order mode has a greater impact, which increases the inelastic response and ductility demand. The effects of the brace design parameters on structural performance were also investigated. The optimal design parameters are as follows: the activation displacement is appropriately small; the variable-damping region corresponds to the axial displacement of 1% IDR; the ratio of the prepressed force to initial Coulomb damping force is 1.0–1.1; and the viscous damping coefficient increases. Combining the damage development process of different components, the VD–SCBF can be designed based on its four seismic performance levels to ensure a reliable resilience. [ABSTRACT FROM AUTHOR]

A full-scale 2-story mass timber building was tested on the University of California San Diego Natural Hazards Engineering Research Infrastructure (UCSD-NHERI) uniaxial shake table during the period from June 2017 to September 2017. The main objective of the experimental program was to test the performance of mass timber building designs with different seismic lateral force–resisting systems. The focus of this study is on a building configuration designed using self-centering post-tensioned cross-laminated timber (CLT) rocking walls with U-shaped steel flexural plate energy dissipators. The shake-table tests were designed to subject the building to a series of earthquake ground motions of increasing intensity, ranging from a service-level earthquake to 1.20 times the maximum considered earthquake intensity. Between each ground motion, low-amplitude white-noise excitations were applied to the building, which responded as a quasilinear system. In this paper, two output-only operational modal analysis methods are used to estimate the modal parameters (frequency, damping, and mode shapes) based on acceleration data collected during the white-noise shake-table tests. The correlations of observed damage and repairs performed during the experimental program with changes in estimated modal features are reported. The modal parameters estimated from the testing program are also compared with a linear finite-element model that is used to validate the modal identification results and study the performance of the two system identification methods for CLT rocking structures. [ABSTRACT FROM AUTHOR]

This study investigated the seismic performance of welded stainless steel H-section columns. Ten columns were tested under cyclic horizontal load; their seismic performance was analyzed according to their hysteresis curves, degree of plasticity, and energy dissipation capacity. The test results obtained were used to validate the developed finite-element (FE) model, which was later utilized in parametric studies. In the tests, it was found that the final failure form of all test columns was local buckling. Slenderness of the component plates and axial load ratio were the governing factors which affected the development of plasticity within the cross sections, the energy dissipation density, and the ductility coefficient. The cross-section classification in the relevant European code is discussed in this paper. Based on numerical data, a ductility-based design approach is proposed, which can provide a reference for the seismic design of welded stainless steel H-section columns. [ABSTRACT FROM AUTHOR]

Gusset plates connect the brace and frame in concentrically braced frames (CBFs). Failure at the interface of gusset plates with the beam or column will result in an inability to achieve energy dissipation through brace buckling and yielding of the brace in tension and failure of the connection before the brace. Traditional design methods for the gusset plate beam or column interfaces in CBFs often consider only forces from brace action. Although studies have shown that forces from frame action can be significant, the complex stress distribution in the gusset plate makes it difficult to effectively evaluate their effects. Neglecting or inaccurately evaluating the frame action may result in unreasonable estimation of the forces in gusset plates, leading to failure at the interface connections. In this paper, the brace action and the frame action forces on gusset plates are systematically explored through an experimental test of CBFs. The proposed design method combines two models for brace action and frame action. Finally, the proposed design method is validated against results from CBF experiments. The proposed design method estimates the magnitude and orientation of the gusset plate interface forces with different configurations of CBFs well. [ABSTRACT FROM AUTHOR]