Research On The Seismic Performance Of Existing RC Bridge Columns Retrofitted By ECC Jackets In The Region Of Plastic Hinge

China is an earthquake-prone country,and the seismic design on bridges plays a pivotal role in bridge design.During the peak period of bridge construction in China,many bridges were designed and built based on the Seismic Design Code for Highway Engineering(JTJ004-89),with inadequate seismic protection indicators.Engineered Cementitious Composite(ECC)has the characteristics of high ductility,strain hardening and multiple microcracking,etc.Its application in the field of seismic retrofit can give full play to its material properties and improve the seismic performance of existing bridge piers.The main research contents of this thesis are as follows:(1)The seismic retrofit methods of bridge piers,the material properties of ECC and its current status of research were analyzed and summarized,and the method of using ECC jackets in the region of plastic hinge was proposed to improve the seismic performance of reinforced concrete bridge piers.Using the height and the thickness of ECC jackets,interface bonding method and Basalt fiber reinforced composite(BFRP)mesh as the research parameters,seven bridge pier models with 1/5 scale ratio were designed and constructed,and pseudo-static reversed cyclic loading tests were carried out.(2)Based on the results of the pseudo-static tests,the seismic performance of all specimens,such as damage mode,hysteresis curve,skeleton curve,stiffness degradation and energy dissipation capacity were analyzed.The test results show that the ECC jackets can significantly improve the bearing capacity and displacement ductility of existing reinforced concrete piers;the bearing capacity can be significantly improved by enhancing the interface bonding between the ECC jackets and the existing piers;the slip between the ECC jackets and the existing piers without enhanced interface bonding is more significant and increases the residual displacement of the specimens.(3)A numerical model of reinforced concrete bridge pier retrofitted by ECC jackets in the region of plastic hinge was established based on the fiber element method,and the accuracy of the numerical model was verified by the test results.On this basis,parametric analysis was carried out to investigate the effects of the height and the thickness of ECC jackets on the seismic performance,and the results showed that the thickness of ECC jacket is more obvious for the improvement of bearing capacity and ductility than the height of ECC jacket;the ECC jackets significantly reduces the strength degradation of the longitudinal reinforcement through the lateral restraint effect,thus improving the seismic performance of the bridge pier.