Influence of infill panels on the seismic response of existing RC buildings: a case study

An analytical evaluation of the seismic response of irregular RC buildings with infill panels designed without considering modern seismic provisions is presented in this paper. Many RC buildings have been built in ’60 and ’70 years in Italy (and many other countries), before the seismic code was issued. Such buildings are usually irregular, due to mass and stiffness distribution, and they exhibit torsional effects when subjected to horizontal loads. One of the factors contributing to the torsional effects is the infill panels built on the perimeter of structures. Usually there is no discontinuity between the structure and the infill, so that the stiffness of the structure is largely affected by the distribution of the infill walls that can be irregular both in plan and in elevation. This work presents the effect of masonry infill in the seismic response of pre-code RC buildings. A numerical analysis has been performed on a case study, simulating the seismic response of the structure, including masonry infill panels. The case study of an existing building, rectangular in plan, having a mild mass eccentricity and an irregular distribution of infill panels, and, therefore, a different eccentricity at each storey is selected for the evaluation. The seismic performance of the building has been evaluated comparing the seismic response with the limit conditions provided by Italian Technical Code, both in terms of interstorey drift and of shear capacity. The seismic response of the case-study building is satisfactory in respect to deformation parameters (chord rotation, top displacement, interstorey drift), but exhibit an un-acceptable amount of shear in some of the elements, experiencing "short column" failures. A possible solution for the problem is proposed, by removing some of the partial infill panels, in order to reduce the shear concentration demands and eccentricity.