A new performance-based design methodology for controlled rocking steel frames

Abstract

The damage caused by recent earthquakes has highlighted the limitations of current seismic force resisting systems and design methodologies, which limit seismic forces by accepting structural damage. Controlled rocking steel frames have been proposed as an alternative system that can limit seismic forces while minimizing structural damage. This paper proposes a new performance-based design methodology for controlled rocking steel frames. In the first step of this methodology, post-tensioning and energy dissipation are designed to achieve target peak displacements at multiple seismic hazard levels. In the second step, the peak force demands on the frame members are estimated using a procedure that is based on the modal properties of cantilever beams with uniformly distributed mass and elasticity. These demands can either be satisfied through elastic design or reduced by using multiple force-limiting mechanisms. The proposed design methodology is demonstrated by application to a twelve-storey structure in California. The results of nonlinear time history analyses show that the methodology leads to a design that satisfies the displacement limits, and that it provides good estimates of the peak force demands on the frame members. The methodology also captures the reduction in forces that is achieved by using multiple mechanisms to control the higher mode effects.