Experimental Study And Theoretical Analysis On Seismic Shear Capacity Of PVC-FRP Confined Reinforced Concrete Column

PVC-FRP confined reinforced concrete column is a new type of composite column, which iswinding CFRP strips on the outside of PVC tube as certain hoop spacing, then putting thereinforcement and pouring concrete in the PVC-FRP tube. The results show that the PVC-FRPtube not only can significantly increase bearing capacity and ductility of core concrete, but alsocan enhance its durability. Based on the existing research of static behavior, the experimentalstudy and theoretical analysis on seismic shear capacity of PVC-FRP confined reinforcedconcrete column is developed as emphases.Based on the experiments of eight PVC-FRP confined reinforced concrete columns and twoPVC tube confined reinforced concrete columns under low frequency cyclic loading, theinfluence of failure mode, hysteretic behavior, stiffness degradation, energy dissipation capacity,bearing capacity and ductility on the seismic behaviors, such as axial compression ratio,shear-span ratio and hoop spacing of CFRP strips are analyzed. The failure mode can be dividedinto three types as follows: The flexural failure is observed of PVC-FRP confined reinforcedconcrete columns and PVC tube confined reinforced concrete columns under low axialcompression ratio, the performance of flexural failure is that the longitudinal reinforcement yield,the concrete is crushed, the PVC-FRP tube and longitudinal reinforcement go through largerplastic deformation, with obvious damage warning. The bending-shear failure is observed ofPVC-FRP confined reinforced concrete long columns and short column which is winding thehoop spacing of60mm of CFRP strips under high axial compression ratio, the performance ofthe bending-shear failure is that the longitudinal reinforcement yield, many diagonal cracksappeared on the surface of PVC tube, the CFRP strips is fractured, with obvious damage warning.The brittle shear failure is observed of PVC-FRP confined reinforced concrete short columnwhich is winding the hoop spacing of20mm of CFRP strips under high axial compression ratio,the performance of brittle shear failure is that the longitudinal reinforcement yield, PVC-FRPtube and concrete is crushed, the lateral deformation is small, with no obvious damage warning.The research results showed that, due to the large axial compression, resulting in theload-displacement hysteretic curve of JC20n2-1is steep, experience fewer cycles, lead to brittlefailure, have poor seismic behavior. The rest of load-displacement hysteretic curves of specimensmaintain good stability and plumpness, and specimens have better energy dissipation capacityand seismic behavior. With the increase of axial compression ratio, the stiffness degradation is quickly decreased, equivalent viscous damping coefficient and bearing capacity is increasedcorrespondingly, but displacement ductility factor showed decreasing trend. With the increase ofshear span ratio, the stiffness degradation is slowly decreased, equivalent viscous dampingcoefficient is increased correspondingly, but displacement ductility factor showed decreasingtrend, bearing capacity is decreased. With the increase of hoop spacing of CFRP strips, thestiffness degradation is slowly decreased, equivalent viscous damping coefficient and bearingcapacity is decreased correspondingly, and displacement ductility showed increasing trend.Based on experimental study and stress-strain relationship model of PVC-FRP confinedreinforced concrete, the shear mechanism of PVC-FRP confined reinforced concrete column wasanalyzed based on truss-arch model, the shear bearing capacity calculation model of PVC-FRPconfined reinforced concrete column was derived on this basis. The influence coefficient of shearbearing capacity is introduced due to the change of displacement ductility factor, by means ofmodification of the formula which is used to calculate shear bearing capacity of FRP confinedreinforced concrete column in exiting specification, and then the design formula of shear bearingcapacity of PVC-FRP confined reinforced concrete column under low frequency cyclic loadingis put forward. The calculated values of the proposed formula agree well with the experimentalresults.Based on the constitutive relations of concrete, steel, PVC tube and CFRP, theload-displacement relationship and moment-curvature relationship of PVC-FRP confinedreinforced concrete column was analyzed by using the test fitting and fiber model method, theload-displacement skeleton curves and moment-curvature skeleton curves of PVC-FRP confinedreinforced concrete column are obtained, the calculation of skeleton curves is verified.According to the mechanical characteristics of PVC-FRP confined reinforced concrete column,the hysteresis rules of PVC-FRP confined reinforced concrete column is put forward, and thenthe restoring force model of PVC-FRP confined reinforced concrete column is established. Thepredications of the models agree well with the experimental results.Using finite element analysis software ABAQUS, the constitutive relations of materials arechosen reasonably. The finite element analysis model of PVC-FRP confined reinforced concretecolumn is established. The finite element simulation results agree well with the experimentalresults. On this basis, the mechanical behavior of PVC-FRP confined reinforced concrete columnis analyzed, and the working mechanism of composite is revealed under low frequency cyclicload.