Seismic Retrofit Of Concrete Bridge Piers With UHPC Jacketing

The seismic design and disaster mitigation on bridges have been paid more attention in recent decades worldwide.In addition to the new bridge design,It is imperative to develop and apply more efficient and practical methods for seismic retrofit in the face of a large quantities of old bridges with insufficient seismic fortification.The previous earthquake damage shows that the bridge pier is the most vulnerable component in the earthquake.It is of great significance to improve and develop the existing methods of seismic retrofit for bridge piers.The main research content of this paper is as follows:Summarizing the existing methods of seismic retrofit for bridges piers,and analyzing respective advantages and disadvantages of them.Discussing the possibility of using UHPC material,which has the characteristic of the high strength,high tenacity and long durability,to retrofit the piers by jacketing the foot and providing considerable constraints.Aiming at the low reinforcement ratio piers with insufficient seismic fortification,two measures of seismic retrofit of UHPC wide strip jacketing and multiple strip jacketing are proposed.In combination with the seismic retrofit requirements of the old bridge,five low reinforcement ratio piers are designed and fabricated.One of them is a comparative specimen(no retrofit measures are taken),two are applied with wide strip jacketing and the rest are applied with multiple interval strips jacketing.The retrofit height of specimens is 1 or 2 piers' section widths.By proceeding the quasi-static test for the piers,some phenomena can be seen:UHPC jackets have a significant constraint effect,vulnerable spot forms easily at the boundary of wide stripe UHPC jackets and cushion cap,multiple interval strips jacketing can make flexural cracks develop fully in plastic hinge,if the height of retrofit zone isn't large enough,at the end of loading,the longitudinal bar buckling may become the final failure mode of piers,UHPC jacketing can increase the horizontal resistance of the pier(about 8%~36%),UHPC jacketing can decrease the residual drift of the original pier(about 18%~50%),UHPC jacketing at the height of 1 pier' s section widths can increase the pier's hysteretic dissipation.Based on Opensees software,a simulation calculation model that can reflect the constraints effect of UHPC jacketing was established.The numerical simulation analysis of pier was carried out to analyze the hysteretic characteristics of the specimens under variable amplitude loading and compared with the test results to verify the accuracy of the test results.