A numerical procedure for modeling the floor deformability in seismic analysis of existing RC buildings

In the paper is presented a research study on floor system behavior in existing Reinforce Concrete (RC) buildings under horizontal actions. Generally, vulnerability analysis consists in the study of effective structural behavior of buildings, in order to carry out the assessment, comparing seismic demand and structural capacity. To this purpose, the hypotheses at the base of Finite Element (FE) numerical model, as rigid floor assumption, assume a primary role for the accurateness of seismic analysis results. In the study, after carrying out a preliminary assessment on significant parameters, which influence the floor stiffness, a new numerical simplified procedure has been proposed. Starting by micro-models, made with solid elements, on several simple applications, the behavior of floor system in elastic field has been analyzed in terms of in-plane displacements and a thickness of an equivalent shell of orthotropic material has been defined, usable in macro-model of frame-shell elements. Subsequently, using the procedure proposed, a real case of existing RC buildings has been investigated. The results of linear analysis have been evaluated through their comparison with those obtained by a model where the flexibility of slab is simulated with a more consolidate method like “strut model”. The numerical analyses carried out have enabled to give interesting indications about both the accuracy of rigid floor assumption and assessment of slab elements.