Development of cold-formed steel elements for earthquake resistant moment frame buildings

The development of thin-walled cold-formed steel (CFS) sections as energy dissipative elements for seismic moment-resisting multi-storey frame buildings is presented through FE analysis and experimental work. Studies on different structural levels are undertaken. At the element level, increasing the number of flange bends enhances both the elastic and inelastic behavior, and beams with an infinite number of bends (with curved flanges) show the highest strength, stiffness and ductility. At the connection level, different configurations of CFS beam-to-column connections using through plates are investigated numerically and verified experimentally. In web bolted connections without out-of-plane stiffeners, premature web buckling results in early loss of strength. A minimum of two pairs of vertical stiffeners are identified as essential in the connection region to delay web and flange buckling and produce relatively high moment strength and ductility. This investigation is validated by beam-to-column connection tests using through plates and curved flange beams with different types of out-of-plane stiffeners in the connection region. The results show that the envelope of the hysteretic curves obtained in the tests of the CFS connections can be predicted by the FE analysis. The use of out-of-plane stiffeners can increase the seismic energy dissipation capacity by up to 90%, the moment strength by up to 35% and the ductility by up to 75% when compared with connections without stiffeners. Correspondingly the use of the two minimum pairs of the vertical stiffeners can increase the seismic energy dissipation capacity by 30%, the moment strength by 28% and the ductility by 50%.

► Thin-walled CFS elements can be used as seismic resistant moment frames.
► The development of CFS sections is studied through FEA and experiments.
► Curved flange beam sections show improved moment–rotation behavior.
► Two pairs of vertical stiffeners are essential to delay buckling in connections.