A hybrid force/displacement seismic design method for reinforced concrete moment resisting frames

Abstract

A performance-based seismic design method for plane reinforced concrete (R/C) moment-resisting frames (MRF) is proposed. This method is based on a hybrid force/displacement (HFD) seismic design scheme, which has been successfully applied to the seismic design of steel structures and is extended in this paper to plane RC-MRFs. The proposed HFD method combines the familiar to engineers force-based design (FBD) method, used in all seismic design codes, with the displacement-based design (DBD) method, which efficiently controls the deformation and hence the damage in a performance-based design (PBD) framework. This is accomplished by constructing explicit empirical expressions for a behavior (strength reduction) factor, which incorporates target non-structural and structural deformation metrics such as inter-storey drift ratio (IDR) and member plastic rotation (θpl). Use of this factor in conjunction with the elastic acceleration spectrum of EC8, can produce designs in one step, by simply conducting a strength checking, since the deformation restrictions are automatically satisfied. Those expressions for the behavior factor in terms of target deformation metrics, number of storeys, column to beam strength ratios and beam to column stiffness ratios are derived through extensive parametrical studies involving 38 RC-MRFs, under 100 ordinary ground motions (25 for each of the four soil classes of EC8) for seven deformation targets. Comparison of the proposed method with the EC8 seismic design through examples, with the aid of non-linear time-history (NLTH) analyses, demonstrates its advantages.