The Effect of the Arrangement and Length of the Concrete Shear Walls on the Response Modification Factor (R)

In equivalent static analysis procedure, the design seismic force is affected by the response factor related to the inelastic behavior of the structure. This factor, whose value is used to calculate the amount of the energy damping, absorbed by the structure, depends on some parameters such as ductility and over strength. It is regarded as a constant coefficient for each type of structural systems in seismic codes. However, in dual structural systems, the effect of features like the geometry of the structure and lateral forces  resistance system on this coefficient is not taken into account. This research is aimed at investigating the effect of the arrangementand length of the shear wall in the plan on the response modification factor in dual concrete systems. To do this, 15 concrete buildings as high as 30 to 45 meters were analyzed by nonlinear static method, using Perform 3D software. The initial estimation of the shear wall length was based on resisting 75 percent of the design base shear force by the shear walls. Next, the over strength factors, ductility coefficients, and subsequently the response modification factors of the models were determined and compared to the value used in the design procedure, presented in ASCE7 code. The results indicated that the value of response modification factor, in comparison with the presented value in ASCE7 code, was varied between -18% to +25% over changing the arrangement of the shear walls, and increased for up to +32% by increasing the length of the shear wall in the plan as much as 100% in proportion to the original model.