Seismic design of buildings is generally accomplished based on the results of dynamic analysis by considering a fixed-base support condition. The effect of soil flexibility, on which the building is resting, is usually ignored during its analysis and design phases. The behavior of soil flexibility causes the lengthening of the natural fundamental period due to the overall decrease in the lateral stiffness of a building. Ground motions at the foundation levels of structures differ from those in the free-field as a result of inertial and kinematic interaction effects. An existing RC high-rise building in Dhaka was selected for dynamic analysis considering soil-structure interaction (SSI) effects. 3D FEM model was created in STERRA 3D software to perform nonlinear static pushover analysis to get trilinear stiffness of each story (both direction) .Then developed MDOF lumped mass model in SNAP v6 software to perform dynamic response analysis. Thin layer nonlinear modeling of soil was performed to get the input ground motion at foundation level and horizontal, vertical and rocking spring with the help of kokujiha wave. Sway spring value was almost same but rocking spring value of longitudinal direction was 2.5 times larger than of transverse direction. Natural period of the building with flexible base in longitudinal direction that’s why 3% longer than fixed support condition and transverse direction 6% longer. Base shear and moment was larger than base fixed model mostly up to bottom 3/4 stories and reduce in upper stories. Drift angle increased in mid height of structure than fixed base model. Structural parameters were not significant difference due to good soil condition .So this analytical approach help to consider soil structure interaction effect while designing high rise building in Bangladesh
Keywords: Soil structure interaction (SSI), Trilinear stiffness, MDOF lumped mass model.