Study On Seismic Behavior Of GFRP Reinforced Concrete Beam Column Joints With ECC Material In Joint Area

Joints play an important role in the frame structure,which are subjected to the compound action of tension,bending and torsion at the same time,the damage of the frame structure often occurs in the joint part.In order to solve this problem,a large number of steel bars are often arranged in the nodes in the current project,which causes the steel bars in the core area of the nodes to be crowded,and increases the construction cost and difficulty.However,in harsh environments,because the steel bars in the nodes are often corroded,even if a lot of steel bars are configured,the durability and safety of the nodes are still difficult to guarantee.In order to solve the problem of crowded reinforcement in the core area of the node and easy corrosion of the reinforcement in the harsh environment,it is an effective method to replace the reinforcement with GFRP reinforcement and replace the concrete in the core area and the plastic hinge area with ECC.This paper proposes a GFRP reinforced concrete beam-column joint with ECC in the node area.Compared with the traditional reinforced concrete joint,the GFRP reinforced concrete beam-column joint with ECC in the node area can effectively increase the ultimate bearing capacity of the beam-column joint and reduce the core District with hoop rate,to prevent corrosion of steel bars.Carrying out research on GFRP reinforced concrete beam-column joints with ECC in the node area has far-reaching significance for studying the application of ECC and GFRP reinforcement in beam-column joints and the improvement of beam-column joint safety and durability in harsh environments.The main research contents of this paper are as follows:(1)Material performance tests were carried out on the GFRP longitudinal bars,GFRP stirrups,steel bars,concrete,ECC and other materials used in this paper,respectively,and the tensile strength of GFRP straight bars,the compressive strength of GFRP straight bars,and the tensile strength of GFRP stirrups were measured.Tensile strength,concrete cube compressive strength,ECC cube compressive strength and other material parameters.The results show that the tensile and compressive strain-strain curves of GFRP bars are all a straight line,and the failure modes are all brittle failures.The elastic modulus in tension and compression of GFRP tendons are basically the same.The tensile stress-strain curve of ECC is divided into three stages,which are divided into elastic stage,yield stage and drop stage with the development of cracks,showing good strain-hardening performance.The ultimate tensile elongation of ECC is 5%,which meets the specification requirements.(2)Low-cycle reciprocating load is performed on 1 GFRP bar concrete beam-column joint,a steel-concrete beam-column node configured with ECC material in one node area,and a GFRP bar-concrete beam-column node configured with ECC material in 5 node areas test.The results show that the ultimate flexural bearing capacity of the beam-column joint specimen increases gradually with the ratio of longitudinal reinforcement,the size of longitudinal reinforcement,and the spacing of stirrups in the plastic hinge area.After pouring ECC in the core area and the plastic hinge area,the ultimate bearing capacity,ductility,stiffness and other parameters of the components are significantly improved compared with ordinary concrete specimens.After being subjected to multiple cyclic reciprocating loads,the bearing capacity of the steel bar decreases significantly faster than that of the GFRP bar specimen,indicating that the fatigue performance of the GFRP bar specimen is better than that of the steel bar specimen.(3)The flexural mechanism of the GFRP reinforced concrete beam-column joint with ECC configured in the node area and the calculation method of the flexural bearing capacity are studied,and the concrete type,stirrup spacing,longitudinal The parameters such as the type of reinforcement affect the flexural performance and shear bearing capacity of beam-column joints,and based on the relevant constitutive factors,the calculation method of flexural bearing capacity of GFRP reinforced concrete beam-column joints with ECC in the nodal area and the GFRP with ECC in the nodal area are proposed.Calculation method of crack-resistant bearing capacity of reinforced concrete beam-column joints.