Experimental research on seismic retrofitting of R/C exterior beam-column-slab joints upgraded with carbon fiber reinforced polymer (CFRP) sheets

Abstract

Under seismic action, the most critical part of R/C structures, which were built in the United States before 1970, is beam-column joints. Common deficiencies of these joints could be summarized as; widely spaced column ties, no transverse reinforcement in joint region, inadequate lap splicing in column and insufficient embedment length of positive beam reinforcement in the joint. This research investigates the actual behavior of such joints with an inclusion of transverse beams and a floor slab. Moreover, CFRP wrapping methodologies are developed to improve the seismic behavior of such deficient joints. In order to investigate the effect of CFRP retrofitting on the behavior of exterior beam-column joints, four 2/3-scaled reinforced concrete beam-column subassemblies were produced and tested under constant axial load and reversed cyclic loading. Three of the specimens had floor slabs and one specimen had only transverse beams (without the slab). The specimen that had no floor slab and one of the other specimens with floor slab were tested as control specimens without the CFRP application. The remaining two specimens with floor slabs were retrofitted with CFRP sheets and then tested. Experimental results demonstrated that torsional cracks on the transverse beams and shear deformations within the joint core turned out to be critical especially when the floor slab was included. Slippage of the positive beam reinforcement in the joint region was another significant deficiency observed in the control specimens. CFRP retrofitted specimens exhibited superior behavior in terms of load carrying capacities. Slippage of the positive beam reinforcement was successfully prevented. Beams and columns were also confined by CFRP sheets and their performance was enhanced in terms of shear and torsional strength.