Seismic Behavior of Shear Wall-Frame Systems Considering Foundation Stiffness

In this paper, the influence of foundation stiffness on the seismic behavior of shear wall-frame systems was investigated. First, a basic differential equation was established to account for the interaction between the foundation and superstructure. By solving the equation, the influence of foundation stiffness on the lateral stiffness, inter-story drift, and internal force distribution of the superstructure at the elastic stage was elucidated. Subsequently, the concept and method for determining the range of foundation stiffness suitable for shear wall-frame systems were proposed. By taking a 12-story shear wall-frame structure built on a shallow foundation as an example, a parametric study was performed for various frame-to-wall relative stiffness ratios and foundation stiffnesses. The effect of shallow foundation stiffness on the base shear distribution and energy dissipation of the superstructure was clarified, with results compared with those of the fixed-base model. The analysis results indicated that the degeneration of foundation stiffness due to earthquake damages will result in significant redistribution of internal forces, namely, the internal forces of the walls decrease, while those of the frames increase. In particular, the shear-force and bending moment of the bottom frame columns rise drastically, which may greatly reduce the safety margin and should be considered in practical design.