Seismic repair of RC bridge piers using shape memory alloys

This experimental study focuses on investigating the feasibility of using shape memory alloy (SMA) spiral to conduct emergency repairs on severely damaged reinforced concrete (RC) bridge piers. The studied repair technique can be implemented in less than 24 hours and hence can be used to rapidly restore the functionality of lifeline bridges that are severely damaged by an earthquake. The proposed repair technique can also ensure the safety and structural integrity of important bridges against strong aftershocks. Unlike other repair techniques such as composite jackets, which utilize the concept of passive confinement, this proposed technique relies on the concept of concrete active confinement to enhance the strength and ductility of severely damaged concrete. Research has shown that active confinement is a more superior confinement technique to passive confinement; however, with conventional materials, its fast application on-site in case of an emergency could be a challenge. This study presents an easy and fast method to apply active confinement using SMAs. The thermally activated shape recovery feature of SMAs is used to apply the active confining pressure at the damaged locations. To examine the proposed technique, two 1/3-scale RC columns which were severely damaged are repaired using SMA spirals and retested. The damage sustained by the two columns is localized primarily at the column base (i.e. at the plastic hinge zone), which is typical in seismically damaged slender columns. The damages in both columns are in the form of concrete cover spalling, concrete core crushing, and buckling and rupture of at least one of the longitudinal rebars. The repaired columns are tested under quasi-static cyclic loading. The results are compared with those of the as-built columns. The experimental results show that the repaired columns have fully restored their lateral stiffness, strength and hysteretic energy dissipation capability. The results of this study clearly illustrate the effectiveness of the proposed technique for emergency repair applications.