Numerical Investigation on the Efficacy of CFRP Jackets for Retrofit of Reinforced Concrete Columns with Sparse Stirrups

Columns in reinforced concrete (RC) buildings constructed according to older codes have in general sparsely spaced stirrups. As a result, in case of an earthquake, the longitudinal reinforcement bars under compression are liable to buckling. Retrofit of such columns using carbon fiber reinforced polymer (CFRP) jackets has proved to be a very efficient and easily applied method to reduce the extent of buckling. To decide the effectiveness of a CFRP jacket for retrofit design, reliable prediction of the behavior of the retrofitted specimen is required. This paper presents the preliminary results of a methodology aimed at a finite element (FE) based numerical prediction of the behavior of RC columns with sparse stirrups retrofitted by CFRP jackets when subjected to axial compression. The effect of the thickness of the CFRP jacket, with the geometrical, reinforcement, and mechanical characteristics of both the jacket and the RC columns are investigated. To validate the proposed methodology, experimental results from 1/3-scale tests have been used to reproduce analytically the respective experimental behavior of short RC columns with square and circular cross-sections subjected to axial compression. Both intact RC columns, as well as damaged RC columns with moderately buckled longitudinal reinforcement, have been used. A major challenge encountered is how to model the effect of pre-existing damage including the buckling of reinforcement rebars. The results obtained are encouraging towards the potential of the proposed methodology to numerically estimate the behavior of the retrofitted columns.