Hysteresis behavior of 3D RC exterior beam-column joints strengthened with CFRP sheets and spike anchors

Full-scale 3D exterior beam-column joints lacking shear reinforcement but externally shear-strengthened with carbon fiber reinforced polymer (CFRP) sheets were investigated with respect to their behavior under both gravity and lateral cyclic loadings. For this purpose, three such joints including one control and two experimental ones (strengthened either with CFRP sheets or with both CFRP sheets and spike anchors) were subjected to relevant tests. Prior to CFRP installation, all the externally strengthened specimens were subjected to surface preparation and grooving in order to prevent possible CFRP debonding. The flexural capacity of both the non strengthened and strengthened joints were estimated using a specially-developed analytical method. Comparisons of the lateral load-displacement hysteresis curves and in the test results revealed that, compared to the control, the externally strengthened joints showed enhancements of 30, 222, and 200% in lateral load-bearing capacity, energy dissipation, and secant stiffness, respectively. It was further found that despite the efficacy of the shear retrofit design proposed for 3D exterior connections, those strengthened with the combined CFRP sheets and spike anchors outperformed the ones solely strengthened with CFRP sheets. The sectional analysis results also revealed that the simple method proposed in this study is well capable of estimating bearing capacity in both the control and strengthened connections with reasonable accuracy.