Effect of Seismic Analysis Approach and Provision of Shear Walls on Parameters for Raft Foundation Design

The present work attempts to understand the effect of different methods of seismic analysis on the design of building raft foundation. The study also evaluates the role of shear wall on the foundation response. A ten storey building with raft foundation has been analyzed in STAAD Pro using three different seismic analysis methods, viz., Linear static analysis, Linear dynamic analysis and Non-linear dynamic analysis. Furthermore, building with two different arrangements of shear walls (peripheral and core region) are studied by Non-linear dynamic analysis and compared with the model without shear wall. The raft is modeled with plate elements supported by soil springs using Winkler's approach. To consider the effect of different soil and raft stiffness, three different soil spring values and two raft thickness values have been considered. It has been concluded from the study that linear static analysis yields lower values of all foundation design parameters (viz., base pressure, settlement, foundation bending moment and shear stress) as compared to dynamic analysis. Dynamic analysis yields higher variation in base pressure and settlement distribution, which suggests adopting dynamic analysis approach for obtaining more realistic response, especially for settlement sensitive structures. Further the provision of shear wall has negligible influence on base pressure and settlement of foundation, while maximum bending moment and shear stress in foundation increases. Hence, provision of shear wall may increase cost of foundation, however, considering its role in improving structural integrity, shear walls are deemed important. Further, the increase in soil stiffness and reduction in raft thickness yields higher maximum base pressure and variation in base pressure, which confirms the importance of considering the effect of soil-foundation interaction for design of foundation. It is opined that the findings of the study would help in more realistic foundation design to achieve better performance during its life cycle.