## 1 Introduction  
Experimental research usually presents a valuable insight into the effects of soil-structure interaction (SSI), yet due to high costs it is not always conducted. Some valuable SSI experimental results and sand modelling techniques on including SSI effects in soil-structure systems are available in literature [1; 2; 3]. These types of experiments can be conducted statically or dynamically and in large or small scale, but considering the significant costs of this type of experiments, small scale experiments are more common. Most of the small-scale experiments are conducted in geotechnical centrifuges [4; 5; 6; 7; 8; 9; 10] which result in severe use of interpretation scaling factors of the experimental results. Large scale experiments, on the other hand, are commonly conducted using shaking tables [1; 3] or as static or cyclic experiments [2; 11; 12]. For any SSI experiment, large-scale experiments are encouraged [13; 14] since they describe the behavior of structures more accurately than their small-scale counterparts. Furthermore, the research on buildings with shallow foundations founded on compliant soils is of great importance since a large number of buildings are built in this manner [15; 16].  
One of the available large-scale SSI experiments on compliant soils is TRISEE [17; 18; 19; 12]. Set of large-size experiments was designed to investigate the nonlinear interaction between buildings with shallow foundations and compliant soils during cyclic loading. More information regarding this experiment can be found in the following chapters.  
What is more, performance based seismic design requires complex numerical modelling to reflect the realistic behavior of a building. To achieve this notion, not only structural systems but also foundation soil should be modelled appropriately. It is well known that buildings founded on rock behave differently than buildings on soft soils during seismic events [20; 21; 22; 23]. It is not uncommon in nowadays design practice to model buildings fixed at the base, which is certainly not true for buildings founded on soft soils. During a seismic event, buildings founded on compliant soils can incline, rock, or slide, which in most cases results in seismic energy dissipation that can be interpreted as a mechanism for building protection [24; 25; 26]. Therefore, in some cases, the soft soil layer can function as a seismic isolator under the building, although one must be careful when determining beneficial or detrimental soil effects on the building [26]. To conduct research in the field of soil-structure interaction, both the structural and geotechnical design aspects have to be studied and appropriate simplifications for the structure and soil have to be used.  
Since many buildings are designed without considering SSI, the purpose of this study is to more closely examine how SSI affects the seismic response of a building and how to include it in the non-linear static methods of analysis (like for example the pushover analysis), which are widely used by practicing engineers due to the relatively high degree of accuracy and low computational cost [27; 28; 29; 30]. It should be noted that soil-structure interaction effects in pushover analysis have already been studied by other researchers to some extent [31; 32; 33; 34; 35; 30]. The research comprised in this article present simplified approaches for the modelling of the soil-structure systems tested on large-scale experiments. The proposed modelling approach is further applied to two two-dimensional frames under nonlinear static analysis. The results obtained on soil-structure systems are compared to results on the structure itself which give valuable conclusions regarding the effect of the soil on the frame using simplified modelling methods.