Rigid floor assumption in nonlinear static analysis of reinforced concrete existing buildings

The assessment of Reinforced Concrete (RC) existing buildings is a main problem studied by scientific community, considering the damage caused to building stock during recent seismic events. This problem is mainly due to design made using old codes. In order to verify the suitability of RC existing buildings towards seismic actions, engineers carry out analyses on Finite Element (FE) models, which simulate the structural behavior of buildings study. In this phase, the accuracy of results depend by initial hypotheses assumed on numerical model. Generally, an usual assumption assumed is that of rigid floor, which allows to reduce Degrees Of Freedom (DOF) of structure and consequently to reduce computational effort of analysis. Furthermore, the rigid floor assumption is an important simplification when the building is analyzed in inelastic field through Nonlinear Static (NLS) analysis. Neglecting the previous hypothesis leads to have not uniform loads distribution on numerical model, with consequent inaccuracy of analysis results. The focus of this paper is investigate the effects of the real in-plane floor deformability under horizontal action, varying the distribution of vertical elements stiffness. In particular, this aspect is evaluated on real cases study, considering the effect induced by infill panels on the stiffness of tridimensional (3D) frame buildings.