PERFORMANCE COMPARISON OF RC RETROFITTED INTERIOR BEAM-COLUMN JOINTS WITH CFRP AND STEEL PLATES

Existing reinforced concrete (RC) building structures constructed until the mid-1970’s, prior to the enforcement of modern seismic design philosophies, are expected to behave poorly when subjected to earthquake actions. The response and damage evolution of RC structures when subjected to severe cyclic loading, such as the ones induced by earthquakes, are highly influenced by the beam-column joint behavior, as they are responsible for the force transfer mechanism between columns and beams and restrain the lateral displacement of the columns. The seismic response of existing RC structures with inadequate reinforcement detailing in the beam-column connections can be improved by retrofitting these connections. In the literature several joint retrofit techniques are presented, including concrete or steel jacketing, carbon fiber reinforced polymer (CFRP) wrapping and strengthening with steel profiles, plates or angles. These retrofit techniques aim to avoid the weak-column/strong-beam mechanism by increasing the flexural capacity of the column and also, in some cases, to improve the joint shear capacity. In this paper a series of unidirectional cyclic tests carried out on four full-scale interior beam-column joints with transverse beams and slab, with typical detailing of structures built until the mid-70’s, are described. One specimen is tested without retrofit (control specimen), another is retrofitted with CFRP and the other two are retrofitted with steel profiles and plates. Both retrofit solutions aim to increase the flexural strength of the columns and the joint shear capacity and to avoid the weak-column/strong-beam mechanism identified in the control specimen test. The selective weakening technique is applied to all retrofitted specimens by cutting the slab in both directions around the joint. The main results in terms of lateral forcedisplacement, equivalent damping, ductility and dissipated energy evolution diagrams, as well as damage description at the end of the tests are presented and discussed. The experimental results show that the adopted retrofit solutions can significantly increase the maximum lateral strength, the ultimate ductility and the energy dissipation capacity. Therefore, the improved seismic performance of the retrofitted specimens is evident when compared with the control specimen and consequently demonstrates the need of retrofitting beam-column joints in order to improve the global seismic behavior of existing RC structures.