Compression behavior of concrete columns combinedly confined by FRP externally wrapped Fe-SMA strips

Compared to the traditional passive confinement to strengthen concrete columns, previous studies testified that the active confinement provided by prestressed materials not only can improve certainly the material utilization rate, but also alleviate the hysteresis of confinement stress. Meanwhile, the iron-based shape memory alloy (FeSMA), that performs the shape memory effect, can be utilized as an innovative strengthening method to rapidly apply the active confinement on concrete columns. In this paper, an innovative active strengthening method by using Fe-SMA strips was proposed, which can provide the potential to make emergency repairing for the damaged columns after the earthquake or impact. The compressive behavior of concrete columns separately confined by the passive confinement, the active confinement, and the hybrid confinement was researched by the compression test, and the different net-spacing strips and different layers of FRP strips were considered as well. The compression test was used to explore the compressive behavior of concrete columns that were confined by three different methods: passive confinement, active confinement, and hybrid confinement, and the test also considered different spacing distance strips and different FRP layers. According to the results, these three confinement types can effectively enhance the load carrying capacity and corresponding deformation of stub columns, especially the hybrid confinement. Finally, a verifying calculation was proposed to predict the peak compressive stress of these specimens, serving as a reference for selecting appropriate methods to strengthen concrete columns.