Research On Compressive Behavior Of FRP-confined Concrete Columns

Fiber reinforced polymer/plastic (FRP) composite materials have been widely used for structural rehabilitation and strengthening, especially in the aspect of upgrading concrete columns. As a basic mechanical performance, compressive behavior of FRP-confined concrete columns is of crucial importance. In this thesis, the compressive behavior of three major concrete columns confined with FRP is investigated in detail, which includes behavior of FRP-confined concrete columns under axial compression, behavior of FRP-confined reinforced concrete (RC) columns under eccentric compression and behavior of FRP-concrete-steel hybrid double-skin tubular columns under axial compression.The major contributions of the work presented in this thesis are listed as follows:(1) A unified model for stress-strain relationship of circular and rectangular concrete confined with FRP under axial compression is proposed based on theoretical analysis and regression analysis. The theoretical curves are in good agreement with the experimental curves. A finite element model (FEM) for simulating the behavior of FRP-confined concrete columns under axial compression is proposed based on selecting different concrete constitutive model according to different confinement level and using layered shell to simulate FRP. The numerical results are in good agreement with the experimental results.(2) Extensive collection and evaluation of existing strength and ultimate strain models for concrete columns confined with FRP are presented. The results show that the prediction for strength is more accurate than the prediction for ultimate strain. Among these existing models, the prediction of Campione's strength model for circular specimens with strain-hardening and rectangular specimens with strain-softening are more accurate, and the prediction of De Lorenzis's ultimate strain model for circular specimens are more accurate. Based on maintaining the accuracy of Campione's strength model and De Lorenzis's ultimate strain model and considering the effectiveness of confinement caused by cross-section, improved models for predicting strength and ultimate strain are proposed. The comparison with experimental results and existing models shows that the proposed models are more accurate, simpler and more convenient.(3) A FEM is proposed to simulate the behavior of eccentrically loaded FRP-confined RC columns based on the modified integrated model for steel reinforcement. The numerical results are in good agreement with experimental results. The results of numerical test based on the proposed numerical model show that the maximum stress and strain of concrete in compressive side of mid-section are related to concrete strength and confinement caused by FRP, and additionally, the maximum strain is inversely proportional to eccentricity-to-section height ratios and length-to-section height ratios. Based on numerical simulation study, an analytical model and a design model are proposed to predict the axial force. Comparisons between predicted and numerical results, predicted and experimental results demonstrate the accuracy and validity of the proposed analytical and design models. A simplified model for axial force-bending moment relationship is proposed based on the design model.(4) In plane strain conditions, a theoretical model for stress-strain relationship of concrete confined with FRP and steel double-skin tubes under axial compression is proposed. The theoretical curves are in good agreement with the experimental curves. A FEM for simulating the behavior of FRP-concrete-steel hybrid double-skin tubular columns under axial compression is proposed based on selecting different element type to simulate FRP tube with different production process. The numerical results are in good agreement with the experimental results. The numerical results show that there are three damage types with FRP-concrete-steel double-skin tubular short columns. Finally, the mechanical analysis for FRP-concrete-steel double-skin tubular columns under different loading methods is presented.