The role of the infills in the seismic retrofit of existing buildings using base isolation

Recent seismic events showed the high vulnerability of the existing buildings and the need to improve their seismic performances. Nowadays different techniques for the seismic retrofit of reinforced concrete buildings are available. One of the most effective technique is the base isolation because it aims at reducing the seismic actions transmitted to the super-structure. In the framework of the seismic risk classification it aims at improving the seismic safety index and at reducing the expected annual losses containing the damage to structural and non-structural components. An efficient design of a base isolation system for existing buildings should aim at minimizing the retrofit interventions on the superstructure in order to reduce the level of disruption. This paper deals with the seismic retrofit of a case study reinforced concrete building by means of base isolation. A refined numerical models including the contribution of hollow clay brick infill wall is developed. Nonlinear dynamic analyses are carried out to assess the performance of the building in the asbuilt and base isolated configuration with and without infill walls. A direct comparison between the seismic performance is performed and the results are discussed with the reference to the reduction of the expected economic losses and needs for the intervention on the superstructure