Seismic behaviors of reinforced concrete column confined by bidirectional fiber reinforced polymer composite with anchor

The bidirectional fibers reinforced polymers (FRP) sheets have good tensile properties in two orthogonal direction. Compared with using traditional unidirectional fabrics, the seismic ductility, shear and flexural capacities of strengthened columns confined by bidirectional FRP sheets are simultaneously improved. Based on using bidirectional FRP sheets with fiber anchors, six reinforced concrete columns were tested under low cyclic lateral loading. The experimental parameters included FRP types, layer number and anchorage schemes, which were intended to study the failure mode, seismic performance and material strain of different confined columns. The test results show that the failure mode of the columns changes from shear to bending failure after confinement, and the hoop working strain of bidirectional FRP sheets is less than that of unidirectional FRP sheets under the same layers. The effective strain of longitudinal fibers in bidirectional FRP sheets significantly increases when using FRP anchor, the fiber strain value is about 1.5 times higher than that before the anchorage, which further improves the flexural capacity of confined columns, the bearing capacities of the confined columns increase by 2.9%-7.1% than that before the anchorage. The research results provide guidance for the application of bidirectional FRP sheets in strengthening existing reinforced concrete structure.