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Base isolation of buildings is the most efficient way of designing seismically resistant structures. Application of seismic isolators allows mutually independent movements of the ground and the structure during earthquakes. The application of seismic isolators increases the natural period of vibrations, which reduces the seismic forces in the structure. The paper analyzes the influence of the application of lead rubber bearings on the response of the structure to the action of an earthquake. A reinforced concrete frame structure was analyzed both for the case of base isolation and rigid foundation. Based on the comparative analysis of the natural period of vibrations, base shear seismic forces, displacement of the top level of the structure and relative inter-storey drift, conclusions were drawn about the efficiency of application of this type of seismic isolator. The required amount of ductility of a structure, as well as damage to structural and non-structural elements, is greatly reduced by base isolation.

Structures composed of different substructures and materials are a subject of great research and expert interest. It is the purpose of this research to develop an engineering approach for evaluation of seismic demands and to apply the methodology to reinforced concrete frames with or without masonry infill. This paper deals with combination of reinforced concrete frame and masonry infill wall. It is known that the combined structure resists well to severe earthquakes. In this paper, the influence of masonry infill on the seismic demands of a reinforced concrete frame structure is estimated using nonlinear analysis. A strut model was used to model the masonry infill resistance; the strut model is statically equivalent to the masonry infill wall. Therefore, material properties of the strut element are determined based on material properties of continuous masonry wall and geometry data. The seismic analysis is performed including material nonlinearity of the model. Determination of seismic displacement demands is carried out using an approximate procedure of the nonlinear analysis in N2- method. To make evaluation of masonry contribution two varieties of the models have been studied - 'with masonry infill' and 'without masonry infill'.