Effects of Aspect Ratio on the Observed Hoop Strain Variation in FRP Confined Concrete Cylinders

Confinement of circular concrete columns by circumferential fibre reinforced polymer (FRP) wraps is among the most widely implemented applications of FRP materials for infrastructure. FRPs are wrapped in the hoop direction around the perimeter of concrete columns and bonded in place with an epoxy adhesive; the effect of this is to drastically improve the columns’ strength and deformability, which has clear benefits for axial strengthening, seismic enhancement, and blast damage mitigation. The technique has been applied to many thousands of columns around the world, yet several aspects of the mechanics of FRP-confined concrete remain poorly understood. One area in which additional research is needed is in understanding, explaining, and quantifying the observed variability of hoop strains in the FRP wraps at failure. This paper follows from previous work using a digital image analysis technique to directly measure the variability of both axial and hoop strains over the surface of FRP-wrapped concrete columns. The results of new tests on FRP wrapped cylinders with increasing aspect ratios are presented with a view to understanding and quantifying the factors that influence the variability and effectiveness of FRP confinement for concrete. The focus in the current paper is on the influence of the cylinders’ aspect ratio on observed hoop strains at failure.