Compressive Behavior of Steel-FRP Composite Bars Confined with Low Elastic Modulus FRP Spirals in Concrete Columns

This paper provides an experimental study on the compressive behavior of steel fiber-reinforced polymer composite bars (SFCBs) confined in concrete columns. Thirty reduced-scale concrete columns, reinforced with different longitudinal SFCBs and fiber-reinforced polymer spirals, were tested under monotonic compression. The results showed that the maximum compressive peak stress of the SFCBs was approximately 50% of their tensile strength, and it was generally lower for those SFCBs that had a relatively high postyield stiffness ratio. The postyield stage of the compressive stress-strain curve of well-confined SFCBs did not develop with a stable postyield stiffness as in nonconfined monotonic compression, but first developed with a stiffness almost equal to zero and then increased rapidly until the compressive peak stress point was reached, which was potentially due to the forced transverse deformation effect. Because the actual compressive contribution of the SFCBs in concrete columns could be overestimated due to this effect, a tentative modification method was first proposed in this paper to calibrate the existing compressive stress-strain model of the SFCBs.