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Yunfeng Zhang and Songye Zhu several design basis earthquakes without the need for repair or replacement of SFDB if properly designed.
1. Introduction In the past decade, passive dampers that utilize shape memory alloys (SMA) for energy dissipation have been attracting growing interest in civil engineering, particularly for seismic hazard mitigation application (e.g., Graesser and Cozzarelli 1991; Aiken et al. 1992, 1993; Witting and Cozzarelli 1992; Clark et al. 1995; Whittaker et al. 1995; Higashino 1996; Wilde et al. 2000; Dolce et al. 2000, 2005; Castellano et al. 2001; Ocel et al. 2004; DesRoches et al. 2004; Zhang and Zhu 2007; Zhu and Zhang 2008). For example, Krumme et al. (1995) have developed a SMA damping device termed center-tapped device for passive control of the dynamic response of civil structures. The center-tapped device comprises a simple slider mechanism in which resistance to linear sliding is provided by two pairs of opposed SMA tension elements. Whittaker et al (1995) developed two conceptual designs for SMA dampers, the effectiveness of which to mitigate the seismic hazard was demonstrated by the nonlinear time history analysis of an existing reinforced concrete frame retrofitted using these SMA dampers under moderate earthquake ground motions. Dolce et al. (2000) tested Nitinol-based devices with full re-centering and good energy dissipation capabilities. Their experimental results have shown that SMA braces can provide a performance level at least comparable to those of steel braces, while having an additional self-centering feature. In Italy, superelastic SMA damping devices have also been implemented in several masonry cultural heritage structures to enhance their seismic resistance capacities during recent restoration (Castellano et al. 2001; Indirli et al. 2001). DesRoches and Delemont (2002) have tested the efficacy of superelastic NiTi bars as bridge restrainers to reduce the risk of collapse from unseating of bridge superstructures at the hinges. Additionally, two full-scale partially restrained steel beam-column connections using SMA bars for providing additional energy dissipation were tested by Ocel et al. (2004). The connection consists of four large diameter Nitinol SMA bars connecting the beam flange to the column flange and serve as the primary moment transfer mechanism. The connections exhibited a high level of energy dissipation, large ductility capacity, and no strength degradation after being subjected to cycles up to 4% drift. New trends in seismic design have resulted in proposals of several innovative seismic protection strategies, among which buckling-restrained braces (BRB) and the concept of selfcentering system have recently received a great deal of attention. BRB, which are capable of yielding in both tension and compression, have been developed to overcome the buckling problems of conventional braces in concentrically braced frame (CBF) systems (Clark et al. 1999; Sabelli et al. 2003; Fahnestock et al. 2003; Uang et al. 2004). In comparison with conventional CBFs, BRB frames have much more ductile performance and a larger energy dissipating capacity, and thus are desirable for seismic design and rehabilitation. BRBF has been used extensively for seismic applications in Japan after the 1995 Kobe earthquake (Reina and Normile 1997) and is quickly gaining popularity in the US after the 1994 Northridge earthquake. However, some researchers have identified several potential problems for BRBF (Sabelli et al. 2003; Kiggins and Uang 2004) including large residual story drifts that could be as high as 40% to 60% of the peak drifts (Sabelli et al. 2003) and tendency of