When an earthquake occurs, the surrounding soil and the structural elements can exhibit non-linear behaviour. Usually, only non-linear behaviour of structural elements is evaluated. But, actually, the soil reaches the limit of its linear elastic behaviour before the structural elements. In general, the soil-structure interaction effects are assumed beneficial and thus ignored. Nevertheless, a more precise knowledge of the expected structural seismic response can allow reduce the cost of the structure and improve the earthquake engineering practice. This work concerns the assessment of the effects of non-linear soil behaviour on the seismic demand evaluation. For this purpose, numerical simulations of non-linear dynamic analysis are performed in order to study the role of several parameters on the seismic performance evaluation. This paper presents a summary of the main findings.