Experimental Investigation of Inelastic Cyclic Buckling and Fracture of Steel Braces

Abstract

Results from 18 large-scale tests of steel bracing members are presented to examine their inelastic buckling and fracture behavior as related to the seismic design of concentrically braced frames. The brace specimens include square hollow structural shapes (HSS), pipe, and wide-flange sections. The effect of various parameters, including width–thickness and slenderness ratios, cross-section shape, loading history, loading rate, and grout fill on the performance of these braces is investigated. Among these parameters, loading history, width–thickness ratio and slenderness ratio are shown to have the largest influence on brace ductility. The test data suggest that for some HSS and pipe specimens, current seismic design provision limits on maximum width–thickness ratios may not provide sufficient ductility for seismic design. Effects of loading rate are found to be insignificant, and the grout fill is shown to provide a modest improvement in cyclic ductility. Measurements of brace stiffness, tensile strength and compressive strength compare well with design formulas. Future analytical studies to simulate brace buckling and fracture are outlined as a way to generalize the findings of the physical tests.