Towards a modified displacement-based seismic design of braced reinforced concrete frame structures considering soil structure interaction

The direct displacement-based design (DDBD) method is a well-developed performance-based design method that utilizes displacement as a fundamental parameter to design structures. The robustness of the DDBD method in satisfying the expected performance level of many lateral load-resisting systems has already been evaluated. However, no particular attention has been explicitly paid to the effects of flexible-base systems. This deficiency has become more noticeable since it was proven that soil-structure interaction (SSI) and foundation flexibility might affect buildings’ seismic performance. The structure response can be changed by SSI owing to the interaction between the structure and the soil beneath the system. In addition, the state of the art reveals that most studies on the effects of SSI have been conducted based on the idealization of structural and soil modeling approaches. To this end, the modified direct displacement-based design method (MDDBD) is first developed, adopting an SSI mathematical model to the previously developed DDBD approach. Second, a nonlinear baseline model and the finite element (FE) procedure are developed and validated against a database of well-documented shaking table tests available in the technical literature. Then, several RC-BRB frames with different heights placed on three soil types are designed based on the developed MDDBD method, and their complete FE models are constructed according to the pre-validated numerical model. To evaluate the performance of the proposed MDDBD method, the complete numerical nonlinear SSI models are subjected to the nonlinear time-history analyses (NTHA) with a set of near-fault and far-fault ground motions. The results indicate that the RC-BRB frames considering SSI designed by the proposed MDDBD method can successfully achieve the desired performance objectives. Finally, a promising applicable formula is developed based on the machine learning-based method for predicting lateral induced displacement of the RC-BRB system considering SSI.