Seismic retrofit and repair of reinforced concrete bridge columns using shape memory alloy spirals

This research focuses on examining the use of shape memory alloy (SMA) spirals in the seismic retrofitting and repair of reinforced concrete (RC) bridge columns. The thermally triggered recovery stress of prestrained SMA spirals is utilized to apply large active confinement pressure at the column’s plastic hinge zone to enhance the flexural ductility of vulnerable columns and limit their post-earthquake damage. Although research has proven that concrete active confinement is a more superior technique to passive confinement, its field application using conventional materials is hindered due to several complications related to the method of application. This research focuses on investigating the new concrete active confinement technique using SMA spirals numerically and experimentally, which is rapid, robust and simple. The research work comprises of: 1) Performing numerical analysis on RC columns retrofitted using SMA spirals (active confinement) and Fiber Reinforced Polymer (FRP) wraps (passive confinement) to examine the superiority of the suggested new confinement technique over current confinement techniques, 2) Investigating experimentally the thermo-mechanical behavior of NiTiNb SMA which is used for this research, 3) Testing concrete cylinders wrapped with SMA spirals and Glass-FRP (GFRP) wraps, 4) Conducting quasi-static lateral cyclic tests on four 1/3-scale RC columns retrofitted with SMA spirals and GFRP wraps, 5) Conducting quasi-static lateral cyclic tests on two severely damaged columns that were repaired using SMA spirals as an emergency repair technique, 6) Utilizing the experimental results of the tested columns to develop and validate numerical models for RC columns retrofitted with SMA spirals, and 7) Utilizing the validated models to conduct a comprehensive parametric study on columns retrofitted with SMA spirals. The results of this experimental and numerical work clearly illustrate that using thermally prestressed SMA spirals to apply external active confinement pressure on concrete columns is an effective, simple, robust, and rapid approach to improve the performance of RC bridge columns