Effects of Higher Modes and Degrees of Freedom (DOF) on Strength Reduction Factor in Reinforced Concrete Frames Equipped With Steel Plate Shear Wall

Abstract

The strength reduction factor (Rμ) originated from the ductility, can adjust the lateral strength of Single Degree of Freedom (SDOF) structures such that their ductility demand is bounded to a certain amount. In addition, Rμ is used for determining the response modification factor of the Multi-Degree-Of-Freedom (MDOF) structures. Accordingly, in this paper, two major factors of Rμ caused by ductility and CR representing the ratio of inelastic to elastic displacement in Single Degree of Freedom Structures (SDOF) subjected to horizontal and vertical components of near and far-field earthquakes, are investigated. Furthermore, CR obtained in this study was compared with the C1 factor proposed by FEMA440. The ratio of deflection amplification factor (Cd) to the response modification factor (Cd/Ru) was computed for different ductility levels. Lastly, after a nonlinear study on the SDOF structure, the Rμ factors are taken into account and afterward, these factors are modified comforting to the MDOF structures and a practical relation is proposed. The results indicated that Rμ corresponding to the near and far-field ground motions can be different. In addition, CR does not depend on type of earthquake and is converged to 1 as the period of vibration increases. In addition, the modification factor raises the following an increase in the period as well as ductility demand.