Effect of the vertical component of the earthquake acceleration on the seismic bearing capacity factors of strip footings

In this paper, the effect of the the vertical component of the earthquake acceleration on the seismic bearing capacity factors (i.e. Nq, Ncand Nγ) are investigated by employing the method of stress characteristics. By mixing the differential equations of stress equilibrium and the Moher-coulomb failure criterion, a system of plastic equilibrium equations is obtained. The generated stresses in the soil mass under the foot surface and next to it in limit state is calculated by solving plastic equilibrium equation system with the method of characteristics. Results show that, the effect of the vertical component of the earthquake acceleration in absence of horizontal component will cause reduction of the bearing capacity factors Nq, Nγ; because having no effect on Nc.The effect of the vertical component of the earthquake acceleration associated with horizontal component will cause reduction resonance on the seismic bearing capacity factors. Using the principle of superposition to obtain of the ultimate bearing pressure of the footing can be a safety.