Seismic soil-structure-interaction of a tall building on pile - raft foundation in Dhaka city

Abstract

A suitable numerical model for studying seismic soil-pile-structure interaction (SSPSI) effects for a tall building resting on pile-mat foundation in Dhaka soil using nonlinear time-history analysis has been studied in this research. The key design parameters, such as lateral displacements, inter-story drifts, foundation rotation, natural frequencies, and response spectrums are compared between a fixed base model (ignoring SSPSI effects) and a flexible base model (considering SSPSI effects). Static analysis has also been performed to investigate the settlement of raft foundations and piled raft foundations resting on Dhaka soil. For Dhaka soil, two types of soil profiles have been studied. Soil profile-1 is a combination of cohesive and non-cohesive soil, whereas soil profile-2 contains only cohesive soil. To carry out finite element analysis, numerical modeling software midas GTS NX has been used. A case study from a published paper has been initially validated. After the successful validation of the program, detailed finite element modelling of a 42-storied building with 4- basements resting on Dhaka soil has been conducted. It has been found that the settlement of mat foundation exceeds the allowable limit for tall building resting on cohesive layer of Dhaka soil. In this case, the mat on pile foundation is ideal and economical. Results from the dynamic soil-structure interaction analysis show that although the lateral displacement and inter-story drift for the flexible base model are amplified 8% to 29% compare to the fixed base model, but it does not exceed the allowable limits. Nominal foundation rotation has been found in mat on pile foundation for Dhaka soil. The deviation of peak ground acceleration (PGA) between the code base spectrum and the spectrum established from the numerical model considering three earthquakes is 13% to 40% at the foundation level that is also nominal. It has been observed that a tall building with multiple basements resting on the pile-mat foundation in Dhaka, ignoring soft soil, the conventional design procedure excluding soil-structurer-interaction (SSI) does not demonstrat