A displacement/damage controlled seismic design method for CFT-MRFs

This paper presents a displacement/damage controlled (DDC) seismic design method for composite (steel/concrete) moment-resisting frames (MRFs) consisting of circular concrete filled-steel tube columns (CFT) and composite beams (steel beams connected with concrete floor slabs). The proposed method works within the performance-based seismic design framework. The method requires a reduced number of design iterations and can estimate at a preliminary phase both the inter-storey drift ratio (IDR) and damage index (DI) of members for a given seismic intensity. The method uses empirical expressions derived by means of statistical and sensitivity analysis of a large seismic response databank consists of IDR and DI that cover all the way from elastic behavior to final global dynamic instability and collapse. Time history analysis results of designed examples demonstrate the advantage of DDC to control better the inelastic response of the frames over the conventional force-based seismic design methods. DDC successfully estimates the target IDR as well as limits the DI in beam-to-column joints to avoid excessive plastic damage and deformations at single storeys.