Effect of vertical component of an earthquake on steel frames considering soil-structure interaction

The present study investigated the effects of vertical components of earthquakes on the responses of 5, 15, and 25 story steel frames by taking into account Soil-Structure Interaction (SSI). The frames were modeled on a fixed base and simulated using two shear waves velocities for the soil (100 and 250 m/s according to NEHERP soil code types E and D soils) using a cone model. The nonlinear behavior of the frames was investigated in the presence and absence of the vertical component of an earthquake and the effects of SSI were examined by comparing the results of the latter analysis with and without use of the cone model. The results showed that the vertical component and SSI can increase the axial force on columns by nearly 50%, the vertical displacement of the mid-point of the beams by nearly two-fold, drift of the stories by nearly 40%, and foundation rotation. Story shear was less affected. When soil type E and soil type D were compared, it was found that the effect of the vertical component of earthquakes on the dynamic response of the frames was generally significant.