Multiple-damage state retrofit of steel MRFs with composite beams using a minimal-disturbance arm damper

This study presents a design method for the seismic retrofit and rehabilitation of steel moment-resisting frames (MRFs) with composite steel-concrete beams using the minimal-disturbance arm damper (MDAD). The purpose is to enhance the seismic performance of this type of MRF by controlling both the overall structure deformation (roof and story drifts) and damage of individual members (local ductility). The MDAD imposes adequate strength and stiffness to limit the story drifts to the targeted values as well as redistributes the internal forces in order to delay beam yielding and fracture. The proposed design method for seismic retrofit and rehabilitation of MRFs integrates the member's strength and ductility indices, such as the bending moment and plastic rotation, into the global frame response in terms of overall shear capacity and story drift through equations developed based on beam-column theory principles. The proposed design method aims to retrofit the structure to satisfy multiple performance objectives, such as (1) the delay of steel beam yielding, (2) the reduction of beam plastic rotation, (3) the control of strength reduction in postfracture behavior, and (4) the recovery of overall shear strength after frame rehabilitation. An experimental campaign was also conducted to evaluate the performance of both retrofitted and bare MRFs. The effectiveness of the proposed retrofit and rehabilitation procedure in limiting the story deformation and improving member ductility of the MRFs as well as its efficiency in recovering the overall strength capacity of heavily damaged framed structures was validated.