Effect of Raft and Column Sizes on the Seismic Soil Structure Interaction Performance of Fifteen Storey Midrise Frame Structures

Abstract

Seismic design of structures is usually executed by performing 1D free-field soil response analysis using design spectral acceleration charts given by codes. This method ignores soil structure interaction effects thus affecting structure-foundation-soil system behavior leading to imprecise design. Soil structure interaction refers to the dynamic behavior between the structure, underlying foundation and soil block. To understand the behavior of a 15 storey midrise concrete seismic frame structure rested on raft foundation and founded on silty sandy soil block, 3D nonlinear time history finite element simulations using Abaqus were performed. The effects of raft and column sizes were considered by modeling flexible and fixed based structures. All cases were hit at the bottom by El-Centro (1940) and Northridge (1994) earthquakes. The results were presented in terms of storey lateral deflection, inter-storey drift, shear force, foundation rocking and response spectrum. The results showed that the combination between the structure-foundation-soil natural frequencies along with the soil type used dictate the behavior of the midrise structure as well as SSI effects under the different raft and column sizes used. Therefore, a detailed study considering all above parameters must be performed by engineers to ensure safe and cost-effective designs.