FRP-Confined Concrete Composite Retrofit System for Structural Steel Columns

Fiber-reinforced polymer (FRP)–confined concrete-steel composite columns have been recently introduced as a retrofit technique for structural steel columns. This technique involves placing a two-part FRP tube around an existing steel column and subsequently filling the void between the steel section and the FRP tube with concrete to create a composite column. The composite action occurs due to the concrete encasing the steel section and the FRP confining the concrete. Within this focus, an experimental investigation has been undertaken with the objectives of evaluating the effect of adding confined concrete to encase a steel W section, the effect of using a split-tube system as a practical encasement technique, and the effect of adding shrinkage-reducing admixtures (SRA) to the confined concrete. A total of 18 stub columns comprising six different column types were tested to achieve these objectives. The test results showed that the load-displacement response of the composite columns was similar to that of confined concrete combined with the elastic–perfectly plastic steel contribution. The experimental findings also demonstrated the enhanced composite column performance, including a significant increase in the ultimate capacity using the proposed split-tube retrofit technique. The results also indicated that the use of a SRA in confined concrete has an indistinguishable effect on the confined concrete strength.