Seismic Behavior Of Reinforced Concrete Square Columns Strengthened By Prestressed CFRP-RPC Method

With the continuous development of road and bridge construction in our country,the bridge structure constructed in the early stage of reform and opening up has lagged behind the growing demand of social functions.The main reason for the aging of structures is that the bridge structure constructed in the early stage has low seismic requirements.The effective reinforcement of the pier post earthquake is the key to ensure the normal operation of the bridge structure.Reactive powder concrete(RPC)is a kind of high-performance concrete with high strength,high ductility,high toughness and strong durability,which has great potential in the protection engineering of impact,explosion and other extreme loads.Fiber reinforced plastics(FRP)has the characteristics of corrosion resistance,high temperature resistance,light weight,small heat capacity,high tensile strength,etc.because its thermal expansion coefficient is similar to that of concrete,it is widely used in the reinforcement of concrete structures.Prestressing FRP material is an active way to provide constraints,which can greatly reduce the stress lag caused by ordinary FRP reinforcement,greatly improve the seismic and bearing capacity of concrete columns,and inhibit the development of cracks.Among them,there are few researches on Strengthening RC columns with FRP and RPC increasing section method at home and abroad,including multi-layer CFRP sheets,high prestressing force,high axial compression ratio,etc.,and the researches on Strengthening RC columns with cast-in-place RPC are insufficient.Therefore,this paper mainly carried out the following work:(1)A total of 15 specimens of ordinary reinforced concrete square columns were poured,including 2 unreinforced columns,4 CFRP strengthened columns,9 RPC strengthened columns or composite strengthened columns of CFRP and RPC.Among them,the RPC of 8 specimens is cast-in-place reinforcement,and the RPC of 1specimen is prefabricated reinforcement.(2)The influence of RPC thickness,axial compression ratio and CFRP strengthening method on seismic energy consumption of reinforced concrete square columns will be analyzed.The test results show that RPC,CFRP single reinforcement or both composite reinforcement can significantly improve the ductility and energy dissipation capacity of reinforced concrete square columns.(3)The failure mode of RPC strengthened or composite strengthened specimens is different from that of CFRP strengthened specimens.Under the condition of two different materials,the former shows brittle failure,while the latter is basically plastic failure.(4)Based on the test data,the skeleton curve and hysteretic performance of some strengthened columns are analyzed.By combining the theoretical analysis with the test data,considering the axial compression ratio,RPC thickness,coefficient of variation of CFRP and other factors,the Trifold restoring force model of the strengthened columns is obtained.The calculation results are in good agreement with the test values.