Effects of Freedom Degrees on Behavior Factor in Reinforced Concrete Moment-Resisting Frames with Steel Plate Shear Wall

The influence of the strength reduction factor due to nonlinear behavior (Rμ) on the lateral strength of Single-Degree-Of-Freedom (SDOF) structures causes to limit the displacement ductility demand to the predetermined maximum tolerable ductility. In addition, Rμ is used for determining the behavior factor in Multi-Degree-Of-Freedom (MDOF) structures. Following this, in this paper, Rμ and the inelastic displacement ratio (CR) for equivalent SDOF systems under strike-parallel (NF-SP) and strike-normal (NF-SN) components of near-field ground motion, and also far-field (FF) ground motion were assessed. Furthermore, CR obtained by this study was compared with C1 proposed by FEMA440. The deflection amplification factor-to-behavior factor ratio (Cd/Ru) for different ductility levels was computed. After evaluating nonlinear effects of SDOF structures based on Rμ factors, these factors for MDOF structure were modified considering higher mode effects, and a simplified practical expression was proposed to estimate the base shear modification factor. The results indicated that Rμ, corresponds to near and far-field ground motions can be different. In addition, CR does not depend on type of earthquake, and it converges to 1 by increasing the period of vibration. In addition, modification factor can be increased with period and ductility demand.