Soil–Structure Interaction-Based Comparative Study of Footing Types for Tall Buildings Using STAAD.Pro

Abstract

The soil–structure interaction (SSI) affects tall reinforced concrete (RC) buildings' seismic and gravitational load responses by altering the stiffness, natural period and load distribution of soil–foundation–structure systems. Traditional design methods often ignore SSI and rely on fixed base conditions, which can result in one-sided predictions for foundation demands. The present study attempts to address this with a systematic SSI based comparative finite element analysis (FEA) of four isolated footing geometries – Rectangular, Square, Oval, Elliptical – in an irregular gravity and seismic loaded G+5 tall building in accordance with the IS 1893 (Part I):2016 and using STAAD.Pro. The Winkler approach to the subgrade reaction is used to model SSI, where each footing contains a distributed elastic springing that represents the interaction between the medium strength soil and the foundation. Four FE models were analysed with the same loading conditions as mentioned, where the dead load = 5 kN/m2, live load = 4 kN/m2, seismic Zone-II parameters (Z = 0.10, I = 1.5, R = 5, medium soil, Sa/g = 2.5, Ah = 0.0375). The following four structural response parameters are assessed: maximum shear force, maximum axial force, Y-direction support reaction, which is proportional to maximum soil bearing pressure, and maximum deflection which is equivalent to the soil bearing pressure-induced settlement of the foundation caused by SSI. Results show that the Oval footing has the best SSI compatibility for all the response parameters, which are discussed below: Maximum shear force= 0.554 kN (which is 95.3% less than Rectangular footing) Maximum axial force= 1.388 kN (which is 89.6% less than Rectangular footing) Maximum force of support reaction= 1.718 kN (which is 83.7% less than Rectangular footing) Minimum deflection= 0.23 mm (which is 48.9% less than Rectangular footing). An S.O.R.-based cost analysis also shows that the cost of reinforcement (INR 12,72,584) in the Oval footing is minimum (7,953.65 kg) as compared to Rectangular footing, which is around 15.9% minimum. The geometry of the footing as described in the IS 1893:2016 code for seismic loading of tall RC buildings, is recommended as the most SSI compatible, structurally efficient and economical isolated footing geometry for tall buildings on medium soil.

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