Dynamic performance of extended pile-shafts is sensibly affected by the soil surrounding the pile. Thus, soil-structure-interaction effects cannot be neglected in the seismic design of such structures. Incremental Dynamic Analyses (IDAs) are performed in order to evaluate the effects of ground motion duration and soil non-linearity on the performance of the single column bent in different soil profiles. Three types of soil, saturated clay and sand in either saturated or dry state, with different void ratios, are investigated. A Beam on a Nonlinear Winkler Foundation able to account for cyclic soil degradation-hardening, soil yielding, slack zone development as well as radiation damping is used in the analysis. Results of IDAs are presented in terms of stress resultants arising along the piles and in terms of displacements at the top of the column. To illustrate the influence of non linear phenomena on the overall seismic response, results are compared with those obtained from a linear model.