With critical lessons drawn from past major earthquakes, the engineering community is appealing for a fundamental shift in the existing design philosophy for structures in seismic zones. One strategy is to endow structures with self-centering (SC) capability. While the concept of SC structures is not new, many novel technologies have been recently emerging that are more efficient, compact, and cost-effective; on the other hand, growing controversy and dispute have also been appearing with deepening investigations. This paper presents a critical review of the evolution of SC technologies and systems for both researchers and practitioners, with an emphasis on post-tension (PT), high-performance spring, and shape memory alloy (SMA) strategies. These SC technologies, together with various energy dissipation options, form the basis of a large part of the newly proposed SC philosophies. This review also includes typical SC structural members such as beam-to-column connections, braces, dampers, shear walls, bridge piers, and isolation bearings, followed by a discussion on the dynamic behavior from a system-level point of view. Available design approaches for SC structures are also touched upon, and practical applications that have emerged over the past decades in several countries including Canada, China, New Zealand, and the US are presented. This paper concludes with an executive summary that covers technological advances, knowledge gaps, and future research directions.

A hybrid self-centering braced frame equipped with shape memory alloy-based self-centering braces (SMA-SCBs) and viscous dampers is proposed to achieve enhanced seismic performance. Based on the proposed hybrid strategy combining the contributions of SMA-SCBs and viscous dampers, this paper investigates the advantages of such hybrid self-centering braced frames in achieving the desired maximum inter-story drift under a considered seismic intensity. To this end, the influence of design parameters of SMA-SCBs and viscous dampers on hybrid self-centering braced frames is examined through parametric dynamic analyses of equivalent single-degree-of-freedom systems. The analysis results indicate that the post-yield stiffness ratio α and energy dissipation factor β of SMA-SCB, and the contribution of viscous damper show significant influence on the peak displacement responses of hybrid self-centering braced frames. The constant inelastic displacement ratio prediction model for hybrid self-centering braced frames is developed using machine learning algorithms. A performance-based seismic design method is subsequently proposed for the hybrid self-centering braced frames to achieve the target displacement responses based on the developed machine learning models. Two hybrid self-centering braced frames are designed based on the proposed design method. Nonlinear dynamic analyses are conducted to investigate the seismic performance of the designed structures. To highlight the advantages of the hybrid self-centering braced frames, another six-story self-centering braced frame with SMA-SCBs only is also studied in this paper. The analysis results indicate that all the designed hybrid self-centering braced frames can achieve the desired performance objective. Compared to the self-centering braced frame with SMA-SCBs only, the hybrid self-centering braced frames can achieve much smaller base shear demand and absolute floor acceleration responses.

Owing to their outstanding recentering capability, shape memory alloy (SMA) dampers are emerging as promising passive dampers for seismic applications. However, compared to typical seismic dampers, the inherent energy dissipation capability of SMAs is often deemed barely satisfactory. To enhance the damping capacity of SMA dampers, this study suggests combining SMA elements with steel dampers based on bending steel plates. In this new SMA-steel damper, the steel dampers are mainly responsible for absorbing seismic energy, whereas the SMA bars primarily play the role of recovering inelastic deformation. Experimental tests were conducted at room temperature to verify the cyclic behavior of the proposed damper. The hysteretic parameters, such as strength, stiffness, equivalent damping ratio, and residual deformation, are of particular interest and quantified as a function of the loading amplitude. According to test results, the new damper is confirmed to possess desirable recentering capability and high damping. To further understand the damper, numerical simulations were carried out in the finite element (FE) analysis software ABAQUS. The numerical results validated the experimental data. Based on the calibrated FE model, the thickness of the bending steel plate of the steel damper and the diameter of the SMA bars were varied in the parametric analysis to examine its effect on the recentering tendency and damping mechanism.

Superelastic shape memory alloys (SMAs) have inherent properties of complete recovery of large deformation and satisfactory energy dissipation under cyclic loadings. Such properties have attracted wide attention within the earthquake engineering community, especially for the perspective of developing self-centering (SC) structures. SMA braced frames (SMABFs) have emerged in recent years as one of promising SC frames. This paper presents a seismic design methodology for SMABFs using the hysteretic energy spectrum. The underlying principle for the proposed design methodology is that both the total hysteretic energy and accumulated ductility demands in earthquake resistant structures are correlated with the maximum endured deformation. With the quantitative relationship, the seismic performance target, such as the maximum interstory drift ratio, can be readily achieved. The spectra of hysteretic energy and accumulated ductility demands are first constructed in this study for the single-degree-of-freedom (SDOF) systems which represent the global behavior of SMABFs. The SDOF system based results were then utilized for the development of an iterative design procedure for multistory SMABFs. Both 3- and 6-story SMABFs are designed for representative low-to-medium rise building structures and subjected to a suite of earthquake ground motions scaled to the design basis earthquake (DBE) and maximum considered earthquake (MCE) seismic hazard levels. Computational simulation results show that the designed SMABFs satisfy the performance target very well. The proposed methodology is demonstrated to be effective and efficient for seismic design of SMABFs, but could also shed light on other SC structures.