Response Modification Factor of Haunch Retrofitted Reinforced Concrete Frames

Abstract

This paper presents experimental and numerical research carried out on low-rise reinforced concrete (RC) frames that have weaker beam-column joints, which are retrofitted with steel haunches to avoid joint shear hinging, allowing beam-column members to deform inelastically and dissipate energy under seismic excitation. Shake table tests were conducted on four 1∶3 reduced scale two-story reinforced concrete frames, having construction deficiencies that are common in developing countries, which were retrofitted with steel haunches to understand their seismic behavior and retrieve the seismic response parameters. A representative numerical model was prepared in finite-element (FE)-based software SeismoStruct, calibrated against the experiments in simulating the structures’ roof displacement time history response and predicting the peak roof displacement and peak base shear force, which showed promising performance. Further, FE based models were subjected to a suite of spectrum compatible natural accelerograms, which were linearly scaled to multiple intensity levels, to perform an incremental dynamic analysis. The structure capacity curve (base shear versus roof displacement) and response curve (seismic intensity versus roof displacement) were retrieved, which were analyzed to calculate the structure-overstrength-based and ductility-based response modification factors. The derived response modification factor can be employed in a force-based design and assessment of haunch-retrofitted reinforced-concrete frame structures. An example case study is presented for the performance assessment of as-built and retrofitted reinforced concrete frames in various seismic zones.