Displacement-based seismic design of reinforced concrete shear wall buildings.

摘要

A displacement-based design method for the seismic design of symmetric and unsymmetric but torsionally stiff buildings with reinforced concrete shear walls is presented. For the preliminary design of such buildings approximate estimates of the yield displacements of individual walls are required: they are calculated from simple empirical relations that depend only on the geometry of the walls. The relative strengths of the walls are then selected, and based on these the global yield displacement is obtained. The ultimate displacement is determined so as to ensure stability under P-Delta effects, keep the ductility demand within ductility capacity, and limit the maximum storey drift to that specified by the codes in order to achieve the near collapse performance level under specified seismic hazard represented by a uniform hazard spectrum. For a multi storey building the structure is converted to an equivalent single-degree-of-freedom system using an assumed deformation shape to represent the first mode shape. The required base shear strength and the corresponding base moment of the system are determined from the inelastic demand spectrum corresponding to the ductility demand, or the ratio of ultimate to yield displacement. In subsequent iterations a pushover analysis for the force distribution based on the first mode is used to obtain better estimates of the yield and ultimate displacements. When the process has converged, a multi-mode pushover analysis is carried out to find more accurate estimates of the shear demands. For a torsionally stiff unsymmetric building the multi-mode pushover analysis is carried out using only the lateral displacement dominant mode shapes. The contribution of the rotational or torsion dominant mode shapes to the different response parameters is negligible. The evaluation of the two design methods is performed using rigorous nonlinear response history analyses for 20 ground motion records scaled to match the seismic demand represented by the UHS of the city of Vancouver. The results of the nonlinear response history analysis show that: (1) the near collapse performance level is achieved for the symmetric buildings and for each edge of the unsymmetric buildings, (2) the roof displacements that the symmetric building and each edge of the unsymmetric building have been designed to experience are not exceeded except for very few records, (3) the square root of the sum of squares (SRSS) rule for combining the modal contributions somewhat underestimates the base shear, while the absolute sum (ABSSUM) combination rule provides a conservative estimate of the base shear. Thus the design methods developed in this work provide a safe and conservative design for the two types of buildings.