Seismic design of low- and medium-rise chevron braced steel frames

This paper presents two different seismic design approaches for multistorey chevron (inverted V) steel braced frames. The first method complies with current Canadian code provisions in which the beams in the bracing bents must be designed to sustain the forces expected to develop up to buckling of the bracing members. In the second approach, the beams must also resist the gravity loads together with a fraction of the brace loads that are induced after buckling of the braces. This second approach aims at minimizing the degradation in storey shear resistance typically exhibited by chevron bracing subjected to strong ground motions, and it is proposed that such braced frames with reinforced beams be designed for reduced seismic loads. Both design procedures are applied to typical multistorey braced frames to examine their economical impacts. Three different beam strength levels were considered for the second design method. The results show that the saving expected from reducing the seismic loads in the second design approach is generally offset by the increase in beam sizes required by this method. However, the braced frames with stronger beams exhibit a much higher storey shear resistance after buckling of the bracing members has occurred.