Innovative emergency repair study on severely damaged bridge columns using shape memory alloy spirals

Repairing damaged bridge reinforced concrete (RC) columns is imperative to recover safety, functionality and serviceability of a transportation network after earthquakes. Repair time is a key factor especially when it comes to repairing lifeline structures. This experimental study focuses on developing an innovative emergency repair technique using shape memory alloy (SMA) spirals on severely damaged RC columns. The damaged columns are repaired within less than 24 hours by using the proposed emergency repair technique. The currently adopted technologies in repairing damaged RC columns such as using fiber reinforced polymer (FRP) wraps mainly depends on dilation of concrete which is often called passive confinement technique. Installing FRP wraps requires additional curing time, which delays the whole repairing process. On the contrary, this proposed technique utilizes the concept of concrete active confinement, which has been proven to be superior to passive confinement in terms of enhancing seismic performance of RC columns. A robust and rapid method of applying active confinement using SMA spirals is presented. The active confinement pressure is applied at the damaged region of RC columns (plastic hinge) by utilizing the unique shape memory feature of pre-elongated SMA spirals. A five step repair process is employed: 1) Removing crushed concrete, 2) Straightening buckled reinforcement and/or coupling ruptured reinforcement, 3) Injecting pressurized epoxy, 4) Applying quick setting mortar, and 5) Installing SMA spirals and heating the spirals. Two reduced-size RC columns are prepared and tested in two phases: 1) The two original column specimens are tested under quasi-static lateral cyclic loading. During the test, severe damage at the plastic hinge zone of the columns are developed in the form of concrete spalling, concrete crushing, and buckling and rupture of longitudinal reinforcement. 2) The damaged columns are repaired with the proposed method, and retested under the same quasi-static cyclic loading within less than 24 hours. The structural performances of the repaired columns are compared with those of the original columns. The experimental study demonstrates that the stiffness and strength of the repaired columns are fully restored, and the proposed repair technique using SMA spirals is efficient and effective.