Study On Joint Connection Of PVC-FRP Confined Concrete Column And Reinforced Concrete Beam

As a new type of composite structure,PVC-FRP confined concrete structure has many advantages,such as high-strength and lightweight,good ductility and durability,good overall performance and easy construction.At present,the research on PVC-FRP confined concrete structure is mainly focus on component level,and the research on the joint of PVC-FRP confined concrete column and reinforced concrete beam is extremely rare.Therefore,the experimental study and theoretical analysis of joint connection between PVC-FRP confined concrete column and reinforced concrete beam are carried out in this paper.The main research contents include the following aspects:The axial compression performance test is conducted on the core area of the joint type I,type II and type III.For the core area of the joint type I,the influence of the the height of joint,the width of the ring beam and the reinforcement ratio of the ring beam on the failure form,the bearing capacity,the deformation,the crack and the equivalent stress and strain of the specimen are mainly analyzed.For the core area of the joint type II,the factors considered are the heigh and diameter of joint,the reinforcement ratio of the steel bars net.For the core area of the joint type III,the factors considered are the heigh of joint,the stirrup rate of hoop and the steel ratio of steel tube.The results show that the failure modes of the core area of the joint type I and II are concrete crush under the action of axial compressive load.When the core area of the joint type I and II are destroyed,the steel cushion plates on the surface of the specimen are sinking obviously,and there are many radial fissures on the upper and lower surfaces of the specimen.The distribution of the cracks on the side of the specimen is different.For the core area of the joint type I and II with a height of180 mm,there are many penetrating vertical cracks and a small amount of horizontal short cracks on the side of the specimen.Many penetrating vertical cracks and a lot of horizontal short cracks appear on the side of the specimen for the core area of the joint type I and II with a height of 240 mm.Many penetrating vertical cracks,a lot of horizontal short cracks and a penetrating transverse long crack appear on the side of the specimen for the core area of the joint type I with a height of 300 mm.Many penetrating vertical cracks,a lot of horizontal short cracks and two penetrating transverse long cracks appear on the side of the specimen for the core area of the jointtype II with a height of 300 mm.For the core area of the joint type III,except for the specimen numbered C1,which crush at the upper end of the column,the other specimens crush at the upper part or middle part of the column.When the specimens are destroyed,the concrete in the middle of the specimens is bulge outwards.And there are a large number of penetrating vertical cracks on the sides of the specimens and many horizontal short cracks which are staggered with vertical fractures.For the core area of the joint type I,with the increase of height,the faster the specimen yield,the ultimate bearing capacity and the deformation capacity gradually decrease,the strain growth rate of the reinforcement and concrete is accelerated,and the peak stress and the corresponding peak strain of the specimen gradually decrease.With the increase of ring beam width and ring beam reinforcement ratio,the yield bearing capacity,ultimate bearing capacity and deformation capacity of the specimens increase gradually.And with the increase of ring beam width and ring beam reinforcement ratio,the strain growth rate of the reinforcement and concrete slows down,the peak stress and strain of the specimens increase gradually.For the core area of the joint type II,the yield bearing capacity,ultimate bearing capacity and deformation capacity of specimens reduce gradually with the increase of height.And with the increase of height,the speed of the strain growth of steel and concrete accelerates,the peak stress and strain of the specimens decrease gradually.With the increase of the diameter and the reinforcement ratio of the steel bars net,the yield bearing capacity,ultimate bearing capacity and deformation capacity of the specimens increase gradually.And with the increase of diameter and the reinforcement ratio of the steel bars net,the slower the specimen yield,the increase of the ultimate bearing capacity and the deformability,the increase of the strain growth rate of the reinforced concrete and the concrete,and the peak stress and the corresponding peak strain of the specimen gradually increase.For the core area of the joint type III,the yield bearing capacity,ultimate bearing capacity and deformation capacity of specimens reduce gradually with the increase of height,the reduction of stirrup rate of hoop and the steel ratio of steel tube.And with the increase of height,the the reduction of stirrup rate of hoop and the steel ratio of steel tube,the speed of the strain growth of steel and concrete accelerates,the peak stress and strain of the specimens decrease gradually.On the basis of the local pressure theory,according to the theory of confined concrete and the superposition principle of multiple constraint,introducing the effectof altitude,the formula for calculating the ultimate bearing capacity of the core of joint type I and II is derived.And based on the theories of the confined concrete,according to the limit equilibrium method and the superposition principle of multiple constraint,introducing the coefficient of colligation,the formula for calculating the ultimate bearing capacity of the core of joint type III is derived.On the basis of Mander model,the calculation formula of peak stress,correction parameters of peak strain and the shape parameter of stress-strain curve are put forward in combination with the stress characteristics of the core area.Thus,the equivalent stress and strain relationship model of the core area are established,which is in good agreement with the test results.On the basis of the equivalent stress and strain relationship model,the formulas of calculating crack load in the core of joint type I,type II and type III are proposed.Using the finite element analysis software ABAQUS,the three kinds of finite element analysis model of joint core are established.The correctness of the finite element model is verified by the comparison between the finite element calculations and the test results.On this foundation,the mechanical behavior of three kinds of joint under axial compression load is analyzed by using the model,and the working mechanism of the joint core is revealed.