Unfavourable seismic behaviour of reinforced concrete structures due to soil structure interaction

Abstract

The soil-structure interaction (SSI) effects can substantially alter the behaviour of structures during earthquakes. Implementation of SSI within the seismic analysis often leads to lower stresses in the structure and therefore a more economical design. The recently introduced provisions in European and American codes allow for this type of approach. However, consideration of SSI can also lead to the observation of unfavourable effects (undetectable in a fixed-base analysis) due to the modification of the structure’s dynamic properties. Examples of unfavourable effects include higher global displacements or story drifts, increases of the base or story shear forces, higher post-elastic demands in the structural members or the collision of adjacent buildings separated by an insufficient structural joint. These unfavourable effects can be related to various parameters such as the structural system (frames or shear walls), foundation type (shallow or piles), geometry of the foundation, height of the building, soil type, seismic input, presence of adjacent buildings, etc. Under these circumstances, the integration of SSI into the current structural design becomes essential. As the mathematical formulation of the phenomenon is very complex and involves many parameters, the definition of complete numerical models is difficult. The provisions in the codes are often general and do not give the practicing engineers clear modelling solutions. An analysis of the current situation in the field of SSI is carried out, with a focus on the design of reinforced concrete structures. Based on an extensive literature review, the unfavourable seismic effects and the main parameters that determine them are identified. Conclusions are drawn regarding the situations when SSI should be mandatory and on the different possibilities of implementing SSI in the structural design.