| Strengthening reinforced concrete columns by using Fiber Reinforced Polymer (FRP) composites is proving to be an effective method compared to traditional retrofit methods. It is well known that FRP confinement is very effective for circular sections but much less effective for square or rectangular sections due to the presence of 90 degree corners and long sides. A possible way to increase the confinement effectiveness for rectangular sections is to perform shape modification, which is to modify the rectangular column section into an oval shape that does not have 90 degree corners or long flat sides.; For such a technique to be widely accepted in practice, it is necessary to develop a good understanding of the behavior of FRP-confined modified sections, and make comparisons to regular sections. This research presents both an experimental and theoretical study on the technique of shape modification. The experiments consist of a series of large-scale column tests including circular, square, rectangular and elliptical modified sections. The specimens were wrapped with FRP composite jackets and have been tested in uniaxial compression until failure. Specimens were wrapped with continuous FRP composite jackets as well as FRP strips. Shape modification was implemented using both bonded FRP jackets, and nonbonded FRP jackets with expansive cement concrete. All specimens were tested in uniaxial compression until failure and the detailed test results are presented.; An analytical model based on a Modified Willam-Warnke (MWW) plasticity model and an incremental approach is developed to describe the stress-strain relationship for FRP-confined columns after shape modification. In addition, a general model for FRP-confined concrete is proposed and implemented. The results show good agreement between the model predictions and the experimental results. As an alternative analytical method, the approach of Finite Element Analysis for modeling the FRP-confined concrete is also developed.; Design recommendations are proposed based on the theoretical results and a parametric study regarding shape modification is further investigated. Conclusions are made and recommendations for future implementation and research are proposed. |
