Ana Rita Gião


High Seismic Performance Beam-Column Connection

The present work refers to the study of seismic behavior and retrofitting of beam-column connections. The motivation of this work relates to the need of improve or increase the safety of structures in relation to seismic actions.

In frame structures, the plastic hinges should be formed in beams (weak beam-strong column). Thus, a test campaign was carried out in order to analyze the cyclical behavior of the critical zone of the beam. The reference specimen was a T-beam reinforced concrete, designed to exhibit a normal ductility. In this study, a new cyclic test procedure was implemented in order to reproduce closer demands on a beam element, simulating horizontal actions simultaneously with the vertical forces. The experimental results are presented and analyzed. In addition, a numerical analysis was performed in order to assess the gravity load effect in the hysteretic behavior of the connection and validate the proposed test procedure.

Structural intervention aimed the improvement of seismic performance - "retrofit" - can be achieved through changes in stiffness, strength and ductility. With this assumption, in order to improve the observed experimental behavior, two strengthening solutions of the connection were developed and tested. In the first solution, unbounded post-tension tendons were used in order to reduce the residual deformation observed. An improvement of the hysteretic behavior of the connection was observed due to an energy dissipation capacity increasing associated to a strength improvement (not ductility). In a second stage, in addition to the post-tension system, a strengthening solution of the compression side of the beam by jacketing with UFRG (unidirectional fiber reinforced grout developed within this work) was developed. The jacketing limits the damage associated with the concrete crushing and buckling of longitudinal reinforcement. The experimental results are presented and analyzed.