Seismic bearing capacity of strip footing over spatially random soil using modified pseudo-dynamic approach

Abstract

This paper explores the influence of dynamic behaviour under earthquake loading and soil heterogeneity on the bearing capacity of the strip footing over a horizontal ground of cohesionless soil. A finite element lower bound limit analysis formulation with second-order conic optimisation is used for the analysis. Dynamic behaviour of seismic waves is incorporated using a modified pseudo-dynamic approach. Spatial distribution of soil is generated by discretising the random field of internal friction angle using Karhunen-Loéve (KL) expansion method. The stochastic response is determined using Monte Carlo Simulation technique. Design charts for mean seismic bearing capacity factor and probability of failure of the footing are provided for practical cases of soil heterogeneity and seismic acceleration. It is found that the consideration of high factor of safety, such as 3, also does not ensure that the structure is safe against failure. The dynamic effect of seismic waves is studied by comparing the plastic yielding of soil at various intervals of time per period of lateral shaking (t/T). It is observed that the failure pattern changes with respect to t/T interval and attains maximum yielding at the t/T ratio corresponding to the least magnitude of seismic bearing capacity factor.