Seismic bearing capacity of shallow strip footings in seismic conditions

The seismic bearing capacity factors of shallow strip footings are calculated. The approach used is pseudo-static, where the seismic effects are considered by taking into account static inertia forces. The upper-hound method of limit analysis is used. Two failure mechanisms, referred to as the M1 and M2 mechanisms, are considered for the calculation schemes. These mechanisms are non-symmetrical. M1 consists of a log sandwich composed of a triangular active; wedge, a log-spiral radial shear zone and a triangular passive wedge. M2 consists of an are sandwich composed of a triangular active wedge, a circular radial shear zone and a triangular passive wedge. The solutions obtained are rigorous upper-bound ones in the framework of the limit analysis theory for an associated flow rule Coulomb material. For the static case, the numerical results of the bearing capacity factors show that the M1 mechanism gives the exact well-known solutions of both the N-cS and N-qS factors. This is not the case with the M2 mechanism. However, for the N-gamma S factor, the lowest upper-bound solutions are obtained from the M1 mechanism for phi > 30 degrees and from the M2 mechanism for phi < 30 degrees. For the seismic case, the lowest upper-bound solutions of the seismic bearing capacity factors obtained from both the M1 and M2 mechanisms are presented in the form of design charts for practical use in geotechnical engineering. These results are compared with other authors' results.