Void-filled SHS beams subjected to large deformation cyclic bending

Local buckling and plastic hinges may occur in the compression flange of square hollow-section (SHS) beams under high amplitude cyclic bending arising from earthquakes. Once a local mechanism forms, residual strength rapidly reduces within a few cycles. This is even true for compact sections that have adequate rotation capacity under static bending. This paper compares the behavior of empty, and void-filled, cold-formed square hollow sections subjected to large deformation cyclic bending. A model is developed to estimate the ultimate moment capacity of void-filled SHS beams. The filler material used was normal concrete, low strength concrete, lightweight concrete and polyurethane. Experimental results show that void filling significantly increases ductility - and thus the number of bending cycles SHS beams can be subjected to - in overloaded situations.