Performance Evaluation of Seismic Strengthened Irregular RC–Steel Hybrid Frames

Abstract

New carbon emission requirements have brought about high demand for the retrofitting and strengthening of structures in power generation plants in order to accommodate the installation of pollution control devices. A typical form of such a retrofitted structure is a hybrid RC–steel frame with specific irregularity features. This paper presents the seismic performance evaluation of a representative irregular RC–steel hybrid frame formed by the vertical combination of a newly added steel frame and a preexisting RC frame. The prototype structure originates from a real retrofitting project, and the evaluation is carried out numerically by creating six variants of the hybrid frame retrofitted with different strengthening strategies on the RC frame using nonlinear finite-element modeling. The seismic performance of the hybrid frame structures is comparatively assessed in terms of roof displacement, story drift ratio, residual displacement, and hysteretic energy ratio when subjected to a group of selected earthquake ground motions at different intensity levels. The results show that among the three main types of retrofitting schemes, strengthening the preexisting RC frame with shear walls appears to be most effective in limiting roof and interstory drifts. Strengthening the preexisting RC frame at the local member level tends to be the least effective strategy. Overall, retrofitting the hybrid structure with steel bracings is deemed to be a more robust solution, both in terms of controlling displacements and enhancing hysteretic energy dissipation capacity.