Fiber-reinforced polymer-confined circular concrete columns:: Investigation of size and slenderness effects

Laboratory investigations of the compressive behavior of fiber-reinforced polymer (FRP)-confined concrete columns have generally been carried out using relatively small-scale specimens, and the majority of theoretical models that have been developed so far are based on test data from such specimens. However, the use of small specimens may conceal possible scale effects. In this study, the influence of slenderness ratio and specimen size on axially loaded FRP-confined concrete columns was investigated experimentally, and the results have been compared to theoretical models and experimental results gathered from the published literature. The investigation aims to validate past results obtained from concrete cylinders and to verify existing empirical models as well. Three different specimen diameters and two slenderness (length-to-diameter) ratios, combined with two FRP-confinement materials, were varied as parameters. According to the statistical analysis of the results, it is shown that conventional FRP-confined concrete cylinders can effectively be used to model the axial behavior of short columns. Size effects, however, are clearly evident in very small (approximate to 50 mm diameter) specimens. The usefulness of published results involving such small-scale specimens is therefore questionable, as is the validity of theoretical models and strength predictions based on test data from small-diameter specimens.