Analytical Seismic Performance Of Reinforced Concrete Pier Retrofitted With SMA Wires

In recent years,the frequent occurrence of large earthquakes at home and abroad has resulted in numerous casualties and property losses,seriously affecting social development.As one of the most critical elements in highway transportation infrastructure network,bridges are often the weak link under earthquake.Especially,piers are the most vulnerable part of seismic bridge structure due to their function as the most important lateral resistance component.The failure of piers is mainly caused by the insufficient ductility and shear resistance of plastic hinge area,which is manifested in the insufficient number of stirrups and the insufficient overlap length.In China,there are a large number of reinforced concrete piers based on the old code for seismic design of highway and urban bridges.What's more,the old piers still have concrete cracking,loosening,collapse,steel bars exposed and other diseases because of the different service time and environment.So it is particularly urgent to retrofit the old piers.Shape memory alloy(SMA)has the characteristics of shape memory effect,superelasticity and high damping.It can not only retrofit piers actively without tensioning equipment,but also improve the ductility and energy dissipation capacity.Actively confined piers with SMA has become a new and effective active reinforcement method,but the influence of SMA material characteristics and different reinforcement parameters on the reinforcement effect still needs to be further explored.Based on the pseudo-static test results supported by the National Natural Science Foundation of China(51678110),this paper used OpenSEES to simulate and verify the active confinement of reinforced concrete piers by NiTiNb-SMA.The main research contents and conclusions are as follows:(1)Based on the macro SMA constitutive model and material test results,the mechanical properties of SMA used in this paper were clarified.Considering the characteristics of SMA,the stress-strain analysis model of SMA confined concrete were obtained.Compared with the existing test data,the results were in good agreement with the calculation results of the model proposed in this paper.(2)Based on the established SMA confined concrete model,using OpenSEES finite element software,the simulation of RC cylinder retrofitted with SMA in pseudo-static test was carried out.The simulation results showed good agreement with the test results.On this basis,the influence rules of SMA-confined RC piers under different concrete strength grades,longitudinal reinforcement ratio,slenderness ratio,axial compression ratio,SMA wrap height and SMA confinement pressure were further studied.Then,appropriate parameter design suggestions were given for the follow-up study of SMA-retrofitted piers.(3)According to the analysis and induction of the results of hysteretic curves under different parameters,the three-fold skeleton curves of RC piers actively retrofitted with SMA are determined.Moreover,the corresponding hysteretic rules and stiffness degradation laws are given.Thus,the restoring force model of RC piers actively retrofitted with SMA considering four parameters,i.e.longitudinal reinforcement ratio,slenderness ratio,axial compression ratio and SMA confining pressure,is established.It can provide reference for dynamic analysis of RC piers strengthened with circumferential prestressing SMA.