CFRP retrofit of concrete circular columns: Evaluation of design guidelines

Carbon fiber reinforced polymer (CFRP) composite external wrapping has become an increasing popular strengthening and confining method for deteriorated or damaged concrete structures. The benefits are high strength-to-weight ratio, corrosion resistance, economy of labor and space savings. This study involved a non-linear theoretical modeling of axially loaded concrete columns with external CFRP laminate application. One-layer and two-layer application, and hoop versus inclined application, were considered. The theoretical of representative confined columns were contrasted against corresponding values from design guidelines. It was found that the guidelines significantly under-predict the strength, maximum stress and strain in CFRP confined columns. The extra CFRP layer was helpful in enhancing the column performance. The numerical model axial capacities were in line with published literature. The failure tensile strain in CFRP was quite a bit larger than the manufacturer suggested value. Inclined CFRP application was not as effective as the hoop application. An optimum value of the CFRP confining strength can be recommended to increase the accuracy of the design guidelines. The strain efficiency factor from ACI, which accounts for premature failure of the CFRP jacket, does not take into account the FRP contributions.