Seismic Behaviors Of Reinforced Concrete Column With Different Axial Compression Ratio Strengthened By Bidirectional Fiber-reinforced Polymer

Due to the modification of the code and the degradation of the strength and stiffness of the materials after long-term use,the axial compression ratio of the original design of the column members will increase or even exceed the limit,and easy to form low ductility failure columns under the action of earthquake.Wrapped with bi-directional fiber sheet can strengthen the RC column by bending and shear,and improve the bearing capacity and ductility under high axial compression ratio.Therefore,the seismic behavior of RC columns with different axial compression ratio restrained by bi-directional fiber sheet was studied in this paper.Firstly,axial compression ratio,bi-directional fiber sheet and anchor was considered,eight RC column specimens were tested under low cyclic reciprocating load.The results showed that bi-directional fiber sheet has better integrity than the traditional fiber sheet because of the interaction between circumferential and longitudinal fibers,which is not easy to produce a large number of transverse cracks in failure.In addition,the failure mode of anchor is the process of gradual fracture of anchor rod fiber with the increase of lateral loading displacement.Then,the seismic performance of columns with different axial compression ratio was analyzed.The analysis results showed that after used bi-directional fiber sheet,the hysteretic curve of the RC column was ful er,the pinch effect was improved,and the energy consumption and deformation capacity were greatly enhanced.When the axial compression ratio is 0,0.3 and 0.45,the bearing capacity of restrained columns under the same axial compression ratio is increased by 16.3%,13.5% and 2.7% respectively;the displacement ductility coefficient is increased by 60%,and the displacement ductility coefficients of restrained columns are greater than 3.0.In addition,with the increase of axial compression ratio in a certain range,the bearing capacity of restrained columns increases nonlinearly,but the degradation rate of strength and stiffness increases significantly after peak load,and the ultimate displacement decreases.After anchoring,the restraint effect of bi-directional fiber cloth is significantly improved,and the longitudinal fiber strain of the specimen is increased by more than 1.7 times;The stiffness of the elastic section of the skeleton curve increases,the bearing capacity is further improved,and the yield bearing capacity is increased by 64.4% and 20.4% when the axial compression ratio is 0 and 0.45.Finally,A double broken line model of the flexural capacity of the anchor reinforced column with bi-directional fiber sheet was proposed based on the failure process of anchor and the mechanism of enhancing the flexural capacity.Considering the influence of longitudinal fiber and anchor on the stiffness and bearing capacity of the elastic section,a trilinear restoring force model for RC columns constrained by bidirectional fiber cloth was established and verified.