Effect of Soil Compliance on Seismic Response of Slender Towers Under Rocking Excitations

Parametric analysis of the effect of soil compliance on the response of a slender tower to combined horizontal and rotational (rocking) of induced ground motion excitations is carried out. In contrast to earlier analyses which use theoretical decomposition of seismic wave field to obtain rotations, this study is using 6 degree of freedom ground motion records to carry on time history integration leading to structural response accounting for “true” phase interactions between horizontal and rocking excitations. The analysis leads to conclusion that the more flexible the sub-soil the smaller the response, however this effect is better pronounced for rotational than horizontal excitations. It was also demonstrated that regardless of the soil compliance, rotational component can have either increasing or decreasing influence on the structural internal forces. In the analysed cases of two sets of excitations such different results were obtained. Clearly more credible rotational-horizontal records of seismic strong ground motion are needed.