Experimental Study On Seismic Performance Of Concrete Beam-column Joints Reinforced With Sprayed GFRP

As the power transmission parts of the reinforced concrete frame structure,the jionts charge transfer and distribution of internal force,ensure the integrity of the structure in the whole frame.The role is very important,once destroyed,it may cause the collapse of the entire building.In recent years,the phenomenon of earthquake damage in China shows that a large number of frame joints have a lack of seismic capacity.Therefore,it is necessary to study the seismic reinforcement of the frame joints.As a new reinforcement method for concrete members,the spray GFRP strengthening method not only has the characteristics of light weight,high strength,quick construction and good integrity,but also can effectively improve the ultimate bearing capacity,stiffness and flexural and shear performance of the joints.At present,there are few studies on spray GFRP reinforcement in academia.The main objects of research are concrete beams,columns,walls and plates.There is a lack of research on the reinforced concrete beam-column joints with spray GFRP.In this paper,the experimental and numerical simulation methods are used to study the seismic performance of the reinforced concrete frame joints strengthened with spray GFRP.In the experiment,we made 5 reinforced concrete beam-column joint specimens with low stirrup rates,1 specimens were comparison specimens,the remaining 4 specimens were strengthened with spray GFRP.The pseudo static test of horizontal load of beam column joints was carried out by displacement control to study the seismic performance of the joints before and after the reinforcement,and the influence of the axial compression ratio,the reinforcement thickness and reinforcement area of the spray GFRP on the seismic performance are analyzed.Then,the ANSYS software is used to expand the seismic performance of the joints strengthened by spray GFRP.On this basis,a theoretical formula for shear bearing capacity of the joints strengthened by spray GFRP is established.The main research results are as follows:(1)The spray GFRP strengthens the reinforced concrete beam-column joints,canbe an effective constraint on the joint core area,enhances the shear capacity of the core area,which makes the destruction form of the joints by the joint core shear failure into beam flexural failure.At the same time,the spray GFRP can improve the ultimate bearing capacity,ultimate displacement,initial stiffness and ductility of the joint,and improves obviously the seismic performance of joints.(2)Increasing axial compression ratio can improve the ultimate bearing capacity and initial stiffness,but will reduce the ductility and ultimate displacement;Increasing the reinforcement thickness and area of spray GFRP can not only enhance the ultimate bearing capacity,initial stiffness and ductility of joints,but also constrain the deformation of concrete and restrain the development of cracks.(3)The results of ANSYS finite element simulation are very close to the experimental results.It is shown that the finite element simulation of element type,failure criterion,constraint mode and loading system is feasible for studying the reinforced concrete beam-column joints strengthened with spray GFRP.(4)Based on experimental research and numerical simulation,a theoretical formula for shear bearing capacity of reinforced concrete beamc-olumn joints strengthened with spray GFRP is established.The calculated results are in good agreement with the experimental and numerical results.