Numerical modelling of the soil in seismic design of structures is always a daunting task. The goal of this article is to develop a simplistic numerical modelling technique for shallow founded buildings on compliant soils. An existing large-scale experimental research (TRISEE) was used for calibration. The physical model comprised of a rigid square foundation placed on a sand bed connected to a rigid column and was subjected to a dynamic sine loading. The results from the TRISEE experiment are well known and commonly used by researchers in this field, yet none of the numerical studies were conducted considering the loose sand case. Nonlinear link elements and linear springs were used for representing the soil. It was determined that the soil behavior is highly influenced by the stiffness, selected hysteresis model, and the p-y curve. Considering the software limitations, numerical models represent the experimental behavior in a good manner. Based on the results obtained from the experiment, a case study on a steel frame building with SSI effects included was conducted. Considering the results from this research, the authors recommend implementation of SSI effects into the building’s design phase since they exhibit unfavorable impacts on the seismic behavior and can lead to underdesigned structural elements. However, it has to be emphasized that certain limitations exist due to simplified modelling approaches that were used for this research.

This paper presents new research in the field of nonlinear static seismic analysis and the N2 method for soil-structure systems. The rationale for this study stems from the inclusion of soil-structure systems in simplified displacement-based design methods. The conducted research comprises three parts, including original experimental investigations, the development of numerical models and the validation of results. A new methodology is presented that provides a step-by-step procedure for the implementation of the N2 method on soil-structure systems. Results of a dynamic shake-table test on a simplified scaled structural model founded on compacted dry sand are presented, and a numerical model of the experiment is developed and calibrated with the inclusion of soil-structure interaction effects. This indicates one main significance of this paper, which is the variation between the experimental and the analytical model and how they can be compared. Lastly, a case study was conducted on a numerical model of a 3D steel building. The building was analysed using pushover analysis for a fixed base-case and by considering soil-structure interaction effects. The results of both observed cases were mutually compared and further examined by validating them with nonlinear dynamic analyses. A comparison was conducted considering the inter-story drifts, calculated according to the N2 method and time-history analyses. The results show good agreement when the N2 method is used for buildings on compliant soils. Overall, it was observed that a decrease in the inter-story drifts appears at ground level of the building. This research also provides a framework for future research in the examined field, for instance, on different types of buildings, building typologies and irregularities of the structural system.

Since numerical modelling of soil properties in seismic design of buildings is usually a complex and demanding task, practicing engineers and researchers aim to keep numerical models as simple as possible. Therefore, the goal of this research is to verify soil-structure interaction (SSI) modelling parameters for buildings founded on compliant soils. For this purpose, the results of a largescale SSI experiment were considered. The TRISEE experiment was chosen as a reference since it is well known in the scientific community and commonly used by researchers. In the scope of this experiment, the SSI effects were determined on a simplified model of the superstructure, consisting of a rigid column and foundation slab placed on the sand bed subjected to dynamic loading. Based on these results a refined non-linear numerical model for SSI was developed, in which the soil behaviour was modelled through its stiffness, hysteresis model and p-y curve. The model was implemented in the SAP2000 numerical modelling software which is based on the finite-element method. It has been shown that numerical models represent experimental behaviour with a sufficient degree of accuracy. Since structural models exhibit different dynamic properties when placed on compliant soils, the authors recommend the implementation of SSI effects into the design of buildings in seismically active regions.