Seismic Damage Analysis And Restorative Force Model Of Polyvinyl Alcohol Fiber Cement Based Compositecompsite Column

Ordinary concrete is widely used in civil engineering because of its advantages such as high compressive strength,good modularity,easy materials and low cost.But at the same time,the concrete’s low tensile strength,poor crack resistance,self-weight,plastic deformation ability and other shortcomings affect the seismic performance and use performance of the concrete structure.The research shows that it is an effective way to improve the above problems from the raw material itself.At present,PVA fiber reinforced cementitious composite(PVA fiber reinforced cement composite)PVA-FRCC(abbreviated as PVA-FRCC)has attracted the attention of scholars because of its excellent tensile,bending,cracking,bending,impact toughness,plastic deformation ability and multi-crack cracking characteristics.In this paper,the effects of hop ratio,PVA-FRCC setting range,PVA fiber volume ratio,axial compression ratio and reinforcement ratio on the seismic damage performance of PVA-FRCC columns were studied by pseudo-static tests.The damage performance of PVA-FRCC column was analyzed based on deformation,stiffness,bearing capacity,residual displacement,energy consumption,modified Park-Ang and Kumar damage models,and the failure patterns and crack development of the specimens were analyzed.The performance levels were also classified.Finally,the restoring force model of PVA-FRCC column was established by combining theory with experiment.The specific research contents and conclusions of this paper are as follows:(1)The normal section bending failure occurred to all the specimens,and the protective layer peeling phenomenon occurred to the specimens without fiber,while the integrity of the specimens with fiber was better.With the increase of stirrup ratio,PVA-FRCC height,fiber volume ratio and axial compression ratio,and the decrease of reinforcement ratio,the crack width of the specimen at each stage decreases,but the number of horizontal cracks increases.The number of oblique cracks decreases with the increase of hoop ratio and axial compression ratio and the decrease of reinforcement ratio.(2)By analyzing the hysteresis curve of the specimen,it can be seen that with the increase of fiber volume ratio,PVA-FRCC setting height,fiber volume ratio and hoop ratio,and the decrease of axial compression ratio,the deformation ability,self-reset ability and energy dissipation ability of the specimen all increase.Locally setting PVA-FRCC at the column end can effectively improve the seismic performance of the member,but with the increase of PVA-FRCC setting range,the fiber utilization rate of PVA-FRCC in the distance from the column end decreases.characteristics of the test hysteretic curves and the damage analysis results,and the restoring force model of PVA-FRCC column was established,and the comparison with the test hysteretic curves showed that the two were in good agreement.(3)through the specimen hysteretic curve and skeleton curve analysis shows that(1)enlarging the PVA-FRCC setting height,increase the rate of reinforcement and fiber volume ratio of specimen has a little influence on the yield load and peak load capacity,improve the fiber volume ratio can effectively improve the cracking load of specimen,improve the axial compression ratio and ratio of longitudinal reinforcement and depth of not only can effectively increase the cracking load of the specimens,It can also effectively improve the peak load.(2)Increasing the hoop ratio,increasing the setting height of PVA-FRCC,increasing the fiber volume ratio and reinforcement ratio,and decreasing the axial compression ratio can improve the deformation capacity of the specimens,and reduce the degradation of bearing capacity and stiffness of the specimens.(3)After adding fiber to cement base material,the specimen can still obtain good deformation capacity and energy dissipation capacity,and also have good crack morphology even if the amount of stirrups is reduced.Therefore,a certain amount of PVA fiber can be added to cement base material column to replace part of stirrups to obtain better aseismic performance and service performance.(4)Based on the calculation and analysis of different damage models,it can be seen that the damage index of specimens increases with the increase of cyclic displacement;Under the same cyclic displacement,the damage resistance,damage deformation tolerance,self-reduction ability and residual bearing capacity of the specimen increased with the increase of hoop ratio,PVA-FRCC setting height,fiber volume ratio and reinforcement ratio,or the decrease of axial compression ratio.By comparing the damage models of all specimens,it can be seen that,except for the stiffness model,the calculation results of all the other models show that the damage development of the specimens is slower in the early stage and faster in the later stage.Under the same displacement,the damage indices calculated by different damage models are different.The damage degree of the specimen expressed by the modified Park-Ang damage model is more consistent with the actual situation of the specimen,and can better describe the damage changes of the PVA-FRCC column during the whole loading process.(5)Based on the theoretical and experimental results,the parameters of the degenerated four-line skeleton model of the specimen were determined,and the theoretical calculation formulas for the displacement and load of the feature points were put forward.The calculation results showed that the relative errors at other points were within the acceptable range except for the large errors at the cracking point.(6)The hysteretic rules of PVA-FRCC column were determined according to the characteristics of the test hysteretic curves and the damage analysis results,and the restoring force model of PVA-FRCC column was established,and the comparison with the test hysteretic curves showed that the two were in good agreement.