Seismic Behaviors of Reinforced Concrete Column with Different Axial Compression Ratio Strengthened by Bidirectional Basalt Fiber-Reinforced Polymer (BFRP) Laminates

When existing reinforced concrete (RC) frame structures need seismic retrofitting, composite strengthening abilities including flexural, shear, and compressive load-bearing capacities are often required to be enhanced. The experimental research was conducted to investigate the seismic performance of RC columns confined with bidirectional fibers reinforced polymer (FRP) composite laminates. Three parameters were considered in this study: bidirectional fiber laminates, axial load ratio, and FRP anchors. Eight large-scale column specimens were evaluated experimentally and were subjected to low-frequency full-reversal cyclic lateral loadings up to failure. Experimental results indicated that the typical failure mode of columns confined with bidirectional fiber laminates differed significantly from that of unidirectional fiber laminates. Specimens strengthened with bidirectional fiber laminates exhibited a transition from bending-shear failure to bending failure, which resulted in fuller hysteresis loops, improved pinching behavior, and significantly enhanced energy dissipation and deformation capacity. After the specimen was confined, as the axial compression ratio increased within a certain range, the increase rate of bearing capacity decreased, and the increase of yield bearing capacity was more obvious than that of peak bearing capacity. The increase of axial compression ratio had little effect on the increase rate of displacement ductility, while the energy dissipation capacity increased obviously. The use of FRP anchors can further improve the bearing capacity and energy dissipation capacity of the specimen.