Seismic behavior of HSS bracing members according to width-thickness ratio under symmetric cyclic loading

Abstract

This study examined the effect of the width-thickness ratio (w/t ratio) on the seismic behavior of cold-formed hollow structural section (HSS) bracing members. For this purpose, an experimental study was carried out. Quasi-static reversed cyclic loading was applied to the specimens. The loading pattern for the tests was determined based on a nonlinear dynamic time history analysis of a frame under earthquake ground motions (EQGM). For this purpose, a three-story specially concentric braced frame (SCBF) was designed according to the AISC LRFD manual. The analysis results showed that a displacement history during the EQGM experienced by bracing members is symmetric in compression and tension. This symmetry may be due to the strong beams in the SCBF connecting bracing members. According to the AISC LRFD manual these beams should resist the unbalanced force associated with compression and tension forces from the connected bracing members. This study adopted a symmetric loading history in compression and tension. Eleven specimens were made to satisfy the detail requirements specified in the AISC LRFD manual and the AISC HSS connection manual. This study showed that HSS bracing members with a small w/t ratio could not always guarantee larger energy dissipation capacity than those with a larger w/t ratio. This was due to early fracture at the slotted end of the bracing members with small w/t ratios.