Compressive performance of square and low-strength concrete columns retrofitted with externally-bonded CFRP

Abstract

Strength and ductility of normal-strength concrete columns can be considerably improved through confinement using Carbon Fiber-Reinforced Polymers (CFRP). Low-strength concrete may be found in structures where measured strength is lower than the nominal compressive strength of concrete, old or non-code conforming structures, and low-rise housing located in the countryside. This paper deals with the assessment of compressive behavior of 18 short, square and low-strength concrete columns confined with both externally-bonded CFRP and conventional transverse reinforcement. The studied parameters were steel ratio (2.8 % and 5.6 %) and configuration of transverse steel reinforcement, as well as carbon fiber volumetric ratio (0.3 % and 0.5 %). Test observations showed that confinement using CFRP notably reduced concrete cover spalling and delayed concrete core crushing. Tests results also showed that the mean value in concrete peak strength for the columns with greater volumetric carbon fiber ratio (0.5 %) was 17 % higher than those of columns with the smaller volumetric carbon fiber ratio (0.3 %), and 79 % higher than those of columns without carbon fiber reinforcement. Based on trends of experimental results, an analytical model was developed and presented in this paper. Results of a statistical analysis demonstrated that the proposed model conservatively predicts compressive strength, therefore it is well suited for design purposes.