Cyclic behavior of concrete bridge columns retrofitted with innovative spirals

This experimental study focuses on investigating the cyclic behavior of reinforced concrete (RC) circular columns retrofitted with an innovative active confinement technique. Most of the attempts for applying active confinement using conventional materials have yielded little success due to practical difficulties associated with applying the external pressure on site. This paper investigates the feasibility of using shape memory alloy (SMA) spirals to enhance the flexural ductility and shear capacity of reinforced concrete columns under lateral cyclic loading. Four 1:3 scale RC columns are prepared and tested under quasi-static cyclic loading. Two of the tested columns are retrofitted with SMA spirals. One of these two columns is wrapped with glass FRP (GFRP) sheets in addition to the SMA spirals. For comparison, a column is confined passively with GFRP sheets and another column is tested in its as-built condition. The experimental results show that the actively confined columns exhibit superior performance to passively confined and unconfined columns. This superior behavior is primarily attributed to the increase in concrete strength and ultimate strain associated with active confinement. Also, SMA spirals show an outstanding ability to mitigate the damage sustained by the columns.