Seismic Behaviors Of Reinforced Concrete Square Column Strengthened By Bidirectional Fiber-reinforced Polymer

In recent years,Earthquakes happen frequently in our country.The standard related to seismic safety have been revised by the state.With the updatedof these codes,the seismic grade of reinforced concrete（RC）frame was generally improved,there was a need for bending and shearing composite reinforcement for the columns of existing buildings.The two-way fiber of the bi-directional cloth can bear the tension at the same time,and the RC column restrained by bi-directional cloth can improve the bending and shearing capacity of the column at the same time.In this paper,the seismic performance of reinforced concrete rectangular columns confined by bi-directional fiber cloth is studied through experiments.First of all,the longitudinal fiber of bi-directional cloth can effectively play its mechanical properties need to be anchored.Because of the good compatibility between the same material,So this experiment used fiber anchor to anchor two-way cloth.Referring to the research on the failure mode of fiber anchors,the design method of fiber anchors for RC columns strengthened with bidirectional cloth was proposed.Then,seven RC columns were designed and fabricated,and quasi-static loading tests were carried out.The effects of fiber cloth type,reinforcement amount and reinforcement method on seismic performance were considered.The failure mode of restrained columns and the strain development of bidirectional strain distribution are studied by experiments,and the influence of different parameters on the seismic performance of restrained columns is obtained.In the test,the failure mode of RC columns changed from shear failure to bending failure with the increase of reinforcement amount,and the bearing capacity of restrained columns increased by12.6%-32.9% compared with that of unreinforced columns.In the loading process,the effective change of unidirectional cloth is 0.008-0.012,while that of bidirectional cloth is 0.007-0.011.The results show that the effective strain of the longitudinal fiber of bi-directional cloth can be significantly increased by using fiber rivets,thus increasing the peak load.Compared with the non anchored bi-directional cloth,the longitudinal fiber strain increases from 0.001 ～ 0.003 to 0.004 ～ 0.008,and the yield displacement of the longitudinal reinforcement and the yield load of the restrained column increase after using fiber rivets.The results show that the best reinforcement method of RC column is to use two layers of bi-directional cloth and fiber rivets.Compared with the unreinforced column,the bearing capacity increases by 32.9%,and the displacement ductility increases by 246.7%.Finally,referring to the relevant research at home and abroad,the calculation formula of bearing capacity and displacement ductility coefficient of reinforced concrete rectangular column strengthened with bidirectional fiber sheet is proposed,which provides design suggestions for the structure strengthened with bidirectional fiber sheet,and provides factual basis for the revision of relevant specifications.