Experimental Study On Seismic Behaviour Of RC Piers Using Prestressing Steel Jacket

RC piers are viewed as lateral force resisting members with seismicvulnerability existed in bridge structures. Conventional approaches proposedpreviously for seismic retrofitting of RC piers were faced with limitations forapplication in engineering practice, thus a seismic retrofit technology usingprestressed steel jackets (PSJ) has been proposed in the current paper, aimingat providing active constraint in transverse direction and improving seismicperformance of RC piers. Experimental study on the circular shaped RC piersretrofitted by PSJ has been conducted as follows.(1) Prestressed steel jackets were designed properly for piers with circularcross section, and prestressed tensioning and controlling technology forcircular steel jackets was also developed.(2) Eight retrofitted specimens designed in shear failure pattern were testedunder low cyclic loading, and three main parameters including the axialcompression ratio (n), hoop plate eigenvalue (η) and the prestressing level (α)were considered. Seismic performance of the specimens is evaluated in termsof failure patterns, skeleton curves, ductility, stiffness degradation and energydissipation. It is worth noting that diagonal shear cracking can be significantlyreduced by the adoption of PSJ, the retrofitted specimens were characterizedby flexural failure instead of shear failure pattern, indicating that strength andductility of the piers can be effectively improved. It is also found thatdisplacement ductility factor increases with the increment of prestressinglevel and hoop plate eigenvalue. For instance, Ductility factor of PC5specimen reached up to5.43, with the prestressing level and hoop plateeigenvalue being0.53and0.34, respectively. Slightly increase of the crosssection dimension and lateral rigidity of RC piers retrofitted by PSJ have noinfluence on the shear force distribution in the bridge structure during theearthquake event. (3) Hysteretic model has been developed for RC piers reinforced withprestressing steel plate hoops by means of theoretical analysis and regressionof experimental data. Hysteretic rules for the proposed model wereestablished. Comparison between the analytical and experimental resultsshows good agreement and the proposed restoring force model can accuratelysimulate the hysteretic behavior of the piers retrofitted by PSJ.