Experimental Study On Axial Compressive Behavior Of Large Scale RC Columns Confined By Pre-stressed CFRP Sheets

Fiber reinforced polymer (FRP) composites have been increasingly applied to strengthen civil engineering due to their excellent mechanical properties. One important application of FRP is reinforcement for the concrete columns. The most common reinforcement method is externally bonded FRP sheets, but this method has significantly stress hysteresis, which may affect the strengthening effect seriously. The lateral pre-stressed FRP can avoid this defect, and improve the reinforcement effect through actively confined. The research of columns reinforced by lateral pre-tensioning FRP is still at the exploratory stage. Most investigations focus on the small size concrete columns, but it is unclear whether the conclusions and models developed on small scale cylinders are appropriate for large scale columns due to the size effect. For that purpose, the research results in this paper are as follows:(1) A total of10large scale reinforced concrete columns, including1unconfined specimen,7pre-stressed carbon fiber reinforced polymer (CFRP) confined specimens and2externally bonded CFRP sheets confined specimens, were conducted with various pre-stress levels and different strip spacing in this experiment to investigate the axial compressive behavior of large scale reinforced concrete columns. The results indicated that, compared to the externally bonded FRP sheets method, the axial compressive bearing capacity and the axial deformability of large scale RC columns retrofitted by pre-stressed CFRP were enhanced much more greatly.(2) Based on the data of experiment, the destructive process, failure mode and working mechanism of pre-stressed CFRP confined large scale reinforced concrete columns were investigated. And considering the strength development of longitudinal reinforcement, the confined effect of concrete with stirrups and pre-stressed CFRP, formulas for peak strength, bearing capacity were derived, and the calculate results shows good agreement with the test results. Moreover, in this paper, design recommendations and construction schemes are suggested as guidelines in practical application of this reinforcement technology.(3) Based on the data of experiment and theoretical analysis, the formula of strain model and two kinds of stress-strain model for large scale concrete columns confined by lateral pre-stressed CFRP were proposed. The calculated results agree well with the experimental results, and it could support for related research.