Conventional vs. modified pseudo-dynamic seismic analyses in the shallow strip footing bearing capacity problem

The conventional pseudo-dynamic (CPD) and modified pseudo-dynamic (MPD) methods are invoked to obtain the seismic bearing capacity of strip foundations using the limit equilibrium method, with a two-wedge failure mechanism. A spectral version of the conventional pseudo-dynamic method (SPD) is also invoked by considering the ground motion amplification factor, to be a function of the non-dimensional frequency λ/B and soil damping. Numeric analyses show that bearing capacity results obtained by the MPD and SPD methods are generally consistent. Both experience the same general reduction in bearing capacity with the increase of λ/B, with successive ups and downs corresponding to soil’s natural frequencies. For 5<λ/B<10, SPD and MPD results fluctuated between falling above and below CPD results. For λ/B<2.5, SPD and MPD results were consistent with attenuation of the shear wave, while for 10<λ/B, amplification was exhibited. Results obtained by the CPD method monotonically decrease, due to the fact that CPD fails to inherently consider site effects and damping, and instead and relies on a single factor to consider the ground motion amplification.