Capacity Envelopes for Design of Square Foundations

Abstract

The interacting axial force, V, horizontal shear force, H, and moment, M, are always applied to the columns and supporting foundations. Although it is a typical practise to consider the interplay of these forces when designing structural components, the effect of interaction in the case of sloped foundations is frequently overlooked by current standards and literature. Furthermore, there is virtually little information concerning the seismic capacity of sloped foundations. This study presents a numerical investigation of the V–H–M and V-M1-M2 capacity envelopes of square foundations placed on the top and face of slopes and exposed to seismic action and vertical eccentricity, with the goal of allowing a direct comparison to the capacity of the supported piers. This is accomplished by using nonlinear 3D finite element limit analysis. To produce the V–H–M and V-M1-M2 capacity envelopes, modified ‘Probe' studies are performed for a cohesionless soil. The computed capacity envelopes are compared to their flat ground counterparts. The characteristics of the failure envelopes is explained under various combinations of V, H, M and V, M1, M2. The effect of foundation width and the aspect ratio of the foundation is studied. The effect of soil slope, position of foundation on soil slope, seismic actions and vertical eccentricity and combination of these actions is explained. To show the relative hierarchy of strength of foundation of a typical pier on slope and pier, a Comparing the capacity envelopes of pier and foundation designed for combination of axial and moment on flat ground and slope ground is provided.