Meccanismi di risposta di nodi trave-pilastro in c.a. di strutture non antisismiche

RC buildings constructed in absence of antiseismic codes have both global deficiencies, connected to lack of regularity in plan and elevation, as well as to the possible onset of weak-column mechanism, and local deficiencies, connected to insufficient transverse reinforcement of beams, columns, joints, and to insufficient anchorage. Because of the high social and economic value of buildings is essential to understand which are the fail mechanisms of these non-seismic R/C structures in order to provide useful details towards a possible improvement and retrofit. The main object of the presented research is to estimate the seismic behaviour of a R/C structure, designed and built according to old code provisions using smooth steel bars. The hoops in the joints were omitted, as used in the past. In order to estimate failure mechanisms and ductility behaviour, some representative internal and external R/C beam-column specimens were built and tested in the Structural Department Laboratory of University of Basilicata (Italy). The tests was been performed increasing, up to the collapse, cyclic horizontal loads. The experimental results, presented in this paper, show that the shear collapse of joints is certainly more important for the external joints less then the internal, in which the lateral confinement greatly increases the strength. The bending fail of the internal columns, due to strong beam weak column design, and the external joint shear collapse, have shown the soft storey mechanism vulnerability of these structures.