Compressive behavior of carbon fiber reinforced polymer-confined concrete in elliptical columns

Reinforced concrete columns can be strengthened by a fiber-reinforced polymer (FRP) jacket which provides lateral confinement to the column. This technique is very effective for circular columns, but its effectiveness is much reduced for rectangular columns. One possibility to increase the effectiveness of FRP confinement for a rectangular column is to modify the column section into an elliptical section. For such section modification to be widely adopted in practice, it is necessary to develop a good understanding of the behavior of FRP-confined concrete in elliptical columns. This paper therefore presents the results of an experimental study on FRP-confined concrete in elliptical columns. Test results are first presented, which indicate that although the confining FRP becomes increasingly less effective as the section becomes more elliptical, substantial strength gains from FRP confinement can still be achieved even for strongly elliptical sections. The ultimate axial strain of the confined concrete is also shown to increase as the FRP confinement becomes stronger. Based on the test results, a simple compressive strength model for FRP-confined concrete in elliptical columns is proposed, in which the effect of the section shape is taken into account by a shape factor.