Strengthening Slender Reinforced Concrete Columns Using High-Modulus Bonded Longitudinal Reinforcement for Buckling Control

This paper introduces a model for strengthening slender reinforced concrete columns. The proposed technique aims at controlling second-order lateral deflections using longitudinal high-modulus bonded reinforcement, thereby altering the loading path to intercept the axial load-bending moment (P-M) interaction curve at a higher axial capacity. With the availability of high and ultra-high-modulus carbon fiber–reinforced polymer (CFRP) plates, this approach should be quite efficient according to Euler’s buckling rule, in which column strength is stiffness-controlled. This approach is different from the classical transverse-wrapping method for confinement, a technique that achieves strengthening by enlarging the (P-M) diagram in the compression-controlled region. The proposed model accounts for concrete nonlinearity in compression, cracking in tension, steel rebar plasticity, and certainly geometric nonlinearity, in addition to the possibility of premature CFRP-debonding failure in tension and the lower CFRP strength in compression than tension. The model is validated against experimental results and used in a parametric study to assess the effects of slenderness ratio $\lambda$, axial load initial eccentricity ratio $e_0/h$, CFRP reinforcement ratio ${\rho }_f$, and modulus $E_f$. It was shown that significant gains in axial strength, ranging from 17 to 90%, occur as the magnitudes of $\lambda$, ${\rho }_f$, $E_f$ and $e_0/h$ increase.