The Influence of Base Isolation to the Required Ductility of Soft Storey Buildings

Abstract

The Response Spectrum Analysis of the structures is based on the allowable ductility considered for that structure. In the case of a multi-degree-of-freedom buildings, the required ductility cannot be the same with the allowable ductility; furthermore, the required ductility values are different for different storey. In the case of first soft/weak storey building, the required ductility of this storey is much higher compared to allowable ductility and impossible to achieve. Nowadays there are many cases of existing reinforced concrete structures with the possibility of soft/weak storey. Even new structures are required to have open space at ground floor level as the owners want them for shops or garages usage. This paper analyses the influence of base isolation to the required storey ductility of weak storey buildings. A five storey shear frame type structure is considered as the model. The elastic and elasto-plastic modelling of the structural elements and bilinear modelling of rubber isolators are used. Linear Response Spectrum analysis and Nonlinear Time History analysis are performed in order to determine the required storey ductility for the existing and new soft/weak storey buildings using the SAP2000 computer program. The analysis results show the reduction of the required storey ductility due to the application of base isolation not only in new structures, but in existing structures too. This means that the base isolation technique is a good alternative to be applied in buildings with first soft/weak storey structure.