ABSTRACT
The 1994 Northridge and 1995 Kobe earthquakes caused unanticipated damages to steel moment-resisting frames due to quasi-brittle fractures that developed in and around the welded beam-to-column connections (Leon et al., 1998; Green et al., 2004; Rassati et al., 2004; Hu et al., 2010; Park et al., 2011; Hu, 2008; Hu & Leon, 2011; Hu et al., 2011; Hu, 2014). Therefore, these frames require special attention in order to limit the excessive non-structural damage resulting from unacceptably large lateral displacements, as well as to avoid the problems associated with P-delta effects (Rassati et al., 2004; Hu et al., 2010; Park et al., 2011; Hu, 2008). As a result, many engineers have increasingly started using concentrically braced frames (CBFs) as an economical load-resisting system that promises good seismic performance with reduced lateral displacement. Compared to the moment-resisting frames, braced frames are expected to offer higher lateral stiffness for drift control in the benefit of diagonal bracing members installed (Sabol, 2004; Sabelli, 2001; Sabelli et al., 2003). However, individual braces in the CBF often exhibit limited energy dissipation under cyclic loading because they are susceptible to buckling prior to gross section yielding. In other words, the hysteretic behavior of these braces is unsymmetric in tension and compression, and the braces show rapid strength deterioration when they buckle under compression (Inoue et al., 2001; Watanabe et al., 1988). Moreover, brace bucklingmay cause the sudden collapse of the entire frame structure. The disadvantages of this CBF system can be overcome in case the brace can yield during tension and compression without buckling.
