Analytical and finite element studies on hybrid FRP strengthened RC column elements under axial and eccentric compression

Analytical and finite element studies on the behavior of Reinforced Concrete (RC) column elements strengthened using a hybrid Carbon Fiber Reinforced Polymer (CFRP) laminates and externally bonded fabric is explored in this study. The main objective of this study is to evaluate the effect of hybrid strengthening on the initial and post-cracking stiffness, peak and post-peak behavior, and change in failure modes of RC column elements. Both axial and eccentric loads are considered in this study. Experimental program is carried out by testing the column elements with and without different FRP strengthening. Analytical predictions are obtained using the strain compatibility approach based on the existing constitutive models for unconfined and confined concrete, steel and FRP composites. A numerical model of column elements is developed using a commercial software ABAQUS. The predictions obtained from the analytical and FE analysis were validated with the experimental results. Analytical and FE predictions exhibited a fair correlation with discrepancy of less than 5% when compared to test results. A parametric study is carried out using the validated FE analysis by varying the CFRP fabric ratio, CFRP laminate ratio and their hybrid combinations. Hybrid strengthening technique is found to be more efficient in improving the initial and post-cracking stiffness, strength and ultimate displacement ductility of RC column elements under compression.