Shape effects on the capacity of rectangular footings under general loading

Ultimate limit states under vertical (V), moment (M) and horizontal (H) loading of rectangular footings with varying breadth-to-length aspect ratios (B/L) are compared with predictions for plane-strain conditions. Footing/soil interfaces unable to sustain tension and with unlimited tensile resistance are considered. Finite element and analytical predictions are reported, and results are presented as failure envelopes in VH, VM and VMH load space. Vertical and moment capacity of rectangular footings, with either zero or unlimited tension interfaces, is shown to increase with reducing footing length, for foundations of a given bearing area. For footings unable to sustain tension, footing aspect ratio does not affect the shape of the failure envelope: therefore ultimate limit states of a footing of any aspect ratio can be derived from a unique envelope scaled by the appropriate ultimate limit loads defining its apex points. A closed-form expression is proposed to describe the shape of the normalised VMH envelope. The shape of failure envelopes for footings able to sustain tension is dependent on footing geometry.