Dynamic and equivalent static procedures for capacity design of controlled rocking steel braced frames

摘要

Controlled rocking steel braced frames (CRSBFs) have been proposed as a low-damage seismic force resisting system with reliable self-centring capabilities. Vertical post-tensioning tendons are designed to self-centre the system after rocking, and energy dissipation may be provided to limit the peak displacements. The post-tensioning and energy dissipation can be designed using simple methods that rely primarily on the first-mode response. However, the frame member forces are highly influenced by the higher-mode response, resulting in more complex methods to design the frame members. This paper examines previous proposals and also proposes two new capacity design methods for CRSBFs. The first is a dynamic procedure that requires a truncated response spectrum analysis on a model of the frame with modified boundary conditions to consider the rocking behaviour. The second is an equivalent static method that does not require any modifications to the elastic frame model, instead using theory-based lateral force distributions to consider the higher modes of the rocking structure. Neither method requires empirical calibration. The dynamic procedure is used to design two sets of CRSBFs with three, six, nine, twelve and eighteen stories, one set using a response modification factor of R = 8 and the other using up to R = 20. Based on the results of 800 nonlinear time history analyses, both methods are generally more accurate than the previous capacity design methods and at least as simple to implement. Finally, the displacement results suggest that taller CRSBFs designed using R8 could still limit interstorey drifts to approximately 2.5% at the maximum considered earthquake level in the cases considered. Copyright (c) 2016 John Wiley & Sons, Ltd.