FRP confined square columns under concentric and eccentric loading

The paper presents an investigation into the behaviour of small- and large-scale FRP confined rectangular columns under both concentric and more typical eccentric loading conditions. Experimental results demonstrate a number of conditions which limit the level of confinement which can be achieved. Apart from the expected rupture of the FRP at the column corners, this includes debonding of the FRP, which becomes more extensive as eccentricity increases, and tensile yielding and rupture of steel reinforcement in tension at large eccentricities. Due to the non-uniform nature of confining stresses in square columns, a theoretical basis for the evolution of effective confinement in the concrete throughout the section is presented. This is linked to the observed behaviour. Comparisons with a theoretical model show that for square columns under concentric loading, the predictions are good, but if applied to rectangular columns or columns under eccentric load conditions, the model can be over-conservative.