FRP-Strengthening of Slender Reinforced Concrete Columns

In the past two decades, fiber-reinforced polymer (FRP) composites have emerged in civil engineering as strengthening materials with superior characteristics for the rehabilitation of existing reinforced concrete (RC) structures. It is well-known that bonding unidirectional FRPs perpendicular to the axis of an RC column (i.e. wrapping) can increase the axial load capacity of the column in compression. It is also accepted that bonding the FRPs parallel to the axis of an RC column can only increase its bending capacity, without significant strengthening effect under axial loads. This is true for a short column with low slenderness effects. However for a long (slender) column the story is completely different, where buckling induced failures can govern due to lack of lateral (flexural) stiffness. In fact, the strength of a slender RC column is a function of its slenderness and induced moment due to its lateral deformation and axial load. As a result, the flexural stiffness of a slender column controls its axial strength. The innovative aspect of this proposal, and the key difference from other strengthening approaches, is that it seeks the desired strengthening gain of a slender RC column primarily by enhancing the flexural stiffness of the column by bonding high-modulus longitudinal FRPs. In this research program, large-scale slender RC columns will be prepared and strengthened using high-modulus FRPs mainly in longitudinal direction of the column and will be tested in laboratory under axial loads with low eccentricities. The effect of circular and square cross-sections, slenderness ratio, initial load eccentricity, FRP ratio, FRP modulus, and combination of longitudinal and transverse FRPs will be studied. In addition, an in-depth study will be performed on the mechanics of FRP crushing and debonding failures that may affect the performance of the longitudinal FRPs. A comprehensive analytical modeling will also be developed and verified against the experimental data to study the effect of a broad range of cross sections, boundary conditions, material properties, and fiber orientations. The research program, upon its completion, is expected to quantify the behavior of slender RC columns strengthened with longitudinal FRPs with a range of parameters, to a point that constructive and reliable recommendations can be made to fill the gaps of current design provisions regarding the FRP strengthening of slender RC columns. The results will be highly applicable for manufacturers and practicing engineers. The achievement of the research program not only will serve to elevate Canada to a leadership position in the area of structural rehabilitation, but also will seek innovative and sustainable solutions for the country's deteriorated infrastructure, such as bridges and water front structures with slender columns.