# Nonlinear Seismic Response of Multistory Steel Frames with Self-Centering Tension-Only Braces
## 1 Introduction  
Although conventional earthquake-resistant systems (e.g., ductile moment frames, braced frames, or concrete shear walls) designed conforming to current seismic codes are confirmed to achieve life safety and collapse prevention performances, there is wide consensus emerging within the structural engineering community that preventing collapse is simply not sufficient for a more resilient structure. Because those systems are prone to permanent, nonrecoverable deformations (residual deformations) after a significant seismic event, leading to substantial losses associated with costs of rehabilitation and operational disruption. For example, many structures that suffered damage in the 2011 Christchurch Earthquake had to be demolished because of excessive residual deformations even though they had not collapsed [1]. A study by [PERSON] et al. suggested that for buildings with residual drift greater than 0.5%, it is more economical to demolish and reconstruct them than repair them [2]. To address this drawback with residual deformations, a novel category of seismic-resilient structural system (SRSS) was developed. A typical SRSS generally employs a restoring force mechanism to achieve self-centering (SC), in conjunction with an energy dissipation (ED) mechanism to protect the primary structure. The main approaches to SC can be classified into four categories: rocking systems,post-tensioned moment frames, shape memory alloy (SMA)-based components, and self-centering braces (SCBs). The key aspect of rocking systems, including rocking walls [3; 4] and rocking braced frames [5; 6], is the gap-opening mechanism taking place between the structure and foundation, which softens the structural lateral response without any residual deformations. The gap-opening mechanism can also be applied to beam-column interface to form a post-tensioned moment frame in which the beam is compressed to the side of a column by using post-tensioning (PT) technology [7; 8]. However, both rocking systems and post-tensioned frames may suffer from issues of installation complexity and deformation incompatibility [5; 9]. Superelastic SMAs, characterized by inherent hysteretic damping and spontaneous recentering, have currently emerged as one class of smart materials for achieving SRSS. Various types of SMA-based components, such as connections, dampers, and braces have been proposed [10; 11; 12]. In the family of SRSSs, SCBs are a promising candidate because of their satisfactory SC capability and especially because SC can be developed within the brace elements such that deformation incompatibility can be avoided, and conventional field techniques are sufficient for installation and replacement. [PERSON] et al. [13] were among the pioneers to develop self-centering energy dissipative (SCED) braces. [PERSON] et al. [14] conducted a shake table test to confirm the behavior of SCED braces within structural systems. [PERSON] and [PERSON] [15] adopted Bezier curves to mitigate the sharp stiffness transition in the hysteresis. [PERSON] et al. [16] developed a new nonlinear model for seismic analysis of structures with SCBs. To further improve the recentering capacity, two types of SC-enhanced brace configurations incorporating multiple SC systems, that is, the dual-core SCB [17; 18; 19; 20] and the telescoping SCED brace [21; 22], were developed independently. More recently, pre-pressed disc springs have been utilized to develop SC, by which the limitations in deformability can be improved further [23; 24; 25]. Comparative studies of SCB frames (SCBFs) and buckling-restrained braced (BRB) frames, however, revealed that amplified seismic demands have emerged as a major concern to SCBFs owing to moderate ED capacity depending on the flag-shaped hysteresis loop of SCBs, which was not as full as that of BRBs [26].