Modal behavior factors for the performance-based seismic design of R/C wall-frame dual systems and infilled-MRFs

Abstract

Modal behavior (strength reduction) factors q̅k for the performance-based seismic design of plane reinforced concrete wall-frame dual systems and infilled moment resisting frames are proposed. Instead of using a single and constant behavior (strength reduction) factor q (R) as all modern seismic design codes do, herein are proposed different such factors for the first few significant modes of the structure. Moreover, these q̅k are constructed as functions of period, different deformation targets and soil types and thus, they are suitable for a performance-based design in a force-based design scheme. A linear analysis in conjunction with an elastic acceleration response spectrum with its ordinates divided by q̅k provides a design base shear which is able to produce seismically designed frames which account for both strength and deformation requirements. In contrast to the code-based seismic design procedure which is accomplished in two steps, i.e., first for strength and second for deformation satisfaction, the proposed method eliminates the second step due to its deformational dependent q̅k. Moreover, these q̅k can be used to design for up to four performance levels depending on the design needs. Explicit expressions for q̅k are derived from extensive parametrical studies involving non-linear tiime-history analyses of 19 wall-frame dual systems and 19 infilled moment resisting frames under 100 far-fault historical ground motions corresponding to the four soil classes of Eurocode 8, for six deformation targets and four performance levels. The proposed method is demonstrated and validated with realistic design examples, which show its advantages over the force-based design method of Eurocode 8.