When an earthquake occurs, the surrounding soil and the structural elements can exhibit non-linear behaviour. In common practice, only non-linear behaviour of structural elements is evaluated. But, actually, the soil reaches the limit of its 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 to reduce the cost of the structure and to improve the earthquake engineering practice. This paper concerns the assessment of the effects of non-linear soil behaviour on the structural seismic demand evaluation. For this purpose, non-linear dynamic analyses 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.