A vast majority of the world's reinforced concrete (RC) buildings are designed using prescriptive force‐based methods. In addition to safety, there is growing demand to meet additional performance ...objectives to limit economic losses and minimize disruption after smaller earthquakes. A framework is proposed that allows prescriptive design standards to deliver multi‐objective risk targets. It adopts an explicitly probabilistic approach considering uncertainty in seismic demand and structural capacity. A rational basis for targeting multiple performance metrics is actualized. The framework provides the first step of a practical strategy to migrate to the performance‐based design of buildings in a phased manner. Using the framework, risk‐targeted safety factors (RTSF) are derived in conjunction with the prescriptive design method to meet different target risk spaces. The framework proposes the replacement of importance factor, which does not quantify performance or risk or considers the building typology, with RTSFs. The framework is illustrated using six example RC buildings representing special moment frame typology conforming to prevalent Indian standards. The results indicate that such typology has an annual frequency of collapse of 1 × 10−4, an annual loss‐of‐operationality of 20 × 10−4, and an expected annual loss of 3 × 10−4. For the same typology, a four‐fold reduction requires an RTSF value of 1.6 for collapse risk, whereas the risk of loss‐of‐operationality necessitates a larger RTSF of 2.0. The larger RTSFs for higher performance illustrates additional design requirement that can only be obtained when considering multiple performance objectives. The framework is universally applicable for any lateral load‐resisting system and selected performance metrics.
Force‐based seismic design involves the reduction of elastic spectra by introducing a behavior factor, q. This approach is widespread in engineering practice; however, recent studies have shown that ...structures consistently designed at different sites will not share the same level of seismic risk, which can be defined as the annual rate of the structure failing to meet a seismic performance objective, despite seismic actions having the same exceedance return period at all sites. This paper investigates whether the definition of site‐specific q factors can lead to uniform risk across sites characterized by varying levels of seismic hazard, based on the pushover curves of bare frame reinforced concrete buildings. These pushover curves are used to establish the backbones of equivalent single degree of freedom systems with varying lateral resistance. These systems are fictitiously placed at several Italian sites and their seismic failure risk is computed by integrating their fragility, assessed by means of incremental dynamic analysis, with each site's hazard curve. By assuming an arbitrary risk threshold, the same for all sites, the corresponding lateral strength leading to said threshold is determined and the corresponding behavior factor is back calculated. As expected, risk‐targeted q factors tend to increase with decreasing seismic hazard and are highly sensitive to the shape of the hazard curve beyond the design return period. Coupled with the fact that at low hazard sites lateral strength is determined by detailing for gravity‐load design and minimum code requirements, rather than seismic design actions, the results suggest that q factor‐based design is unsuitable for warranting territorially uniform seismic safety, yet it may be suitable for setting an upper‐bound to the annual failure probability.
•Investigated seismic performance of SMA-based braced frames (SMABs).•Proposed a performance-based seismic design (PBSD) for seismic-resisting self-centering SMABFs.•Considered hysteretic parameters ...and high-mode effect in the PBSD for SMABFs.
This study proposes a performance-based seismic design (PBSD) method for steel braced frames with novel self-centering (SC) braces that utilize shape memory alloys (SMA) as a kernel component. Superelastic SMA cables can completely recover deformation upon unloading, dissipate energy without residual deformation, and provide SC capability to the frames. The presented PBSD method is essentially a modified version of the performance-based plastic design with extra consideration of some special features of SMA-based braced frames (SMABFs). Four six-story concentrically braced frames with SMA-based braces (SMABs) are designed as examples to illustrate the efficacy of the proposed design method. In particular, the variability in the hysteretic parameters of SMAs, such as the phase-transformation stiffness ratio and the energy dissipation factor, is considered in the PBSD method. Accordingly, four SMABFs are designed with different combinations of these hysteretic parameters. The seismic performance of the designed frames is examined at various seismic intensity levels. Results of nonlinear time-history analyses indicate that the four SMABFs can successfully achieve the prescribed performance objectives at three seismic hazard levels. The comparisons among the designed frames reveal that the SMABs with greater hysteretic parameters result in a more economical design in terms of the consumption of steel and SMA materials.
Abstract The post‐earthquake recovery of a community depends on the ability of important buildings to perform their functions. Lifeline and other critical buildings that meet a predictable enhanced ...seismic performance increase the community's disaster risk management capacity. In prescriptive force‐based design standards, the seismic design force for these buildings is typically enhanced using an importance factor depending on the risk category. The present paper proposes an innovative framework based on performance‐based seismic design (PBSD) principles using risk‐targeted importance factors suitable for use with prescriptive standards. The framework decouples probabilistic assessments of building typologies to experts, while the structural designers can continue the conventional design approach. The framework explicitly considers probabilistic seismic demand, uncertainty in the performance of the building, and the inter‐building variation within a particular building typology in seismic performance. Six special reinforced concrete (RC) frame buildings conforming to Indian standards are selected to illustrate the framework. Sensitivity studies on parameter selection are used to establish the framework's robustness. An expression for the importance factors is also proposed. The use of the proposed importance factor expression is shown to meet a wide range of risk targets corresponding to different performance levels. The paper also proposes design factors for enhanced performance objectives suitable for the risk‐targeted prescriptive design. Further, the framework is implemented to estimate the seismic risk associated with existing building typology conforming to prevalent design standards. The assembly‐ and critical‐category RC buildings are found to require higher importance factors for achieving enhanced performance objectives than currently prescribed.
This paper uses computational simulation to investigate the lateral load‐displacement behavior and failure modes of a modern 14‐story reinforced concrete (RC) core wall building. The design complies ...with the minimum code requirements of the current California Building Code, which is based on ASCE 7–16 and ACI 318–14. The computational representation of the building, which accounts for the material nonlinearities of all structural components, employs the beam‐truss model (BTM) for the walls and floor slabs. Analyses of the building model are conducted for static monotonic and cyclic lateral loads using the program FE‐MultiPhys, which provides a user‐friendly implementation of the BTM as an assemblage of rectangular shell macroelements. Two different load patterns, that is, lateral load distributions along the building height, are considered. The analyses provide insights into the evolution of damage and lateral strength degradation and their dependence on the load pattern, while also elucidating the complex interaction between the webs and flanges of the core wall and the system effects associated with coupling between the walls, beams, slabs, and columns. The presentation of the analytical results is accompanied by a discussion on the advantages of the BTM over seismic analysis methods used in current code‐minimum and performance‐based seismic design (PBSD) practice.
AbstractACI 318-19 and ASCE 7-22 specify code-compliant and emulative seismic force-resisting systems (SFRS) including intermediate precast shear wall systems. For the seismic design of a precast ...shear wall system, its successful performance heavily depends on the capacity design of inevitable discrete connections between precast wall panels, thus playing a critical role in controlling yielding to occur within steel reinforcements at the vicinity of intended locations or components. This is imperative for achieving not only ductility but also adequate energy dissipation, ensuring the system can effectively withstand seismic forces. To this end, the overstrength is essentially required to prevent any brittle failure, and the connections designed not to yield can be protected by addressing the 1.5Sy condition as specified in ACI 318-19 and ASCE 7-22. However, there can be a blind spot for the precast connections designed to yield. To this end, this study showed some cases based on practical examples from which a reasonable magnitude of overstrength (Sy) was tentatively recommended for better safety in the seismic design of the intermediate precast shear wall system with precast connections designed to be yielded.
A realistic performance‐based seismic loading protocol called generated sequential ground motion (GSGM) has been developed in this paper. GSGM is a ground motion fabricated from segments of real ...recorded ground motions that could enable the introduction of performance‐based seismic assessment and design to experimental testing in setups such as shaking table testing. It can also significantly reduce the number of nonlinear time history analyses required in performance‐based seismic design. The protocol optimizes the behavioral information output of an experimental test or numerical analysis by incorporating dynamic demands corresponding to design limit states with different probabilities of exceedance (i.e. 10%, 5%, and 2% in 50 years) in a single record. In addition, since the segments are matched to relevant target spectra, the number of ground motions required to estimate the mean response is reduced. This paper presents the algorithm developed to produce the GSGM. The capability of the GSGM to replicate the structural responses produced by code‐compliant suites, and a suite of 100 ground motions as a more robust estimation of the actual response is investigated. The results of the case study bridge pier show that the drift variation of the GSGMs compared to code‐compliant suites is within 10%. Compared to the estimate of the actual response, the drift variation of GSGMs and the code‐compliant suites is 20% and 15%, respectively, and the damage variation is 30% and 15%, respectively. Furthermore, considering other relevant intensity measures when producing GSGMs can reduce these variations. This study suggests that the GSGM can replicate structural responses of the current code procedures.
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