Effects of unconfined concrete strength on FRP confinement of concrete

Research has shown that fibre reinforced polymer (FRP) wraps are effective for strengthening concrete columns for increased axial and flexural load and deformation capacity, and this technique is now used around the world. The experimental study presented in this paper is focused on the mechanics of FRP confined concrete, with a particular emphasis on the influence of the unconfined concrete compressive strength on confinement effectiveness and hoop strain efficiency. An experimental programme was undertaken to study the compressive strength and stress-strain behaviour of unconfined and FRP confined concrete cylinders of different concrete strength but otherwise similar mix designs, aggregates, and constituents. This was accomplished by varying only the water-to-cement ratio during concrete mixing operations. Through the use of high-resolution digital image correlation to measure both axial and hoop strains, the observations yield insights into the mechanics of FRP confinement of concretes of similar composition but with varying unconfined concrete compressive strength.