Stability analysis of CFRP-wrapped concrete columns strengthened with external longitudinal CFRP sheets

The external confinement by CFRP wrappings is a very efficient method to increase the load-carrying capacity of round concrete columns. Nevertheless, the serviceability of such columns under loads exceeding the strength of unconfined concrete is limited by different factors. One of them is the reduced stability of the columns due to the significantly reduced tangent elastic modulus inactive loading. To increase the critical load of buckling instability of concrete columns, an additional longitudinal composite reinforcement can be used. In this paper, the stability and strength of concrete columns confined by circumferential wrappings and strengthened with a longitudinal external CFRP reinforcement are studied. Plain and confined columns of length 300 and 1500 mm were tested. Theoretical predictions show that the additional longitudinal reinforcement is efficient in improving the stability of confined columns in the region of moderate slenderness. The prediction for the ultimate strength and stability of the columns coincides rather well with experimental results.