| In recent years, concrete structure strengthened by carbon fiber reinforced polymer (CFRP) is becoming hot spots in engineering circles, experimental study on this method has been developed by many scholars. The design codes for concrete structures reinforced by CFRP cloth was published in 2003 and 2006, including "Strengthening Design Codes of Concrete Structures" (GB50367-2006) and "Technical specification for strengthening concrete structures with carbon fiber reinforced polymer laminate" (CECS146-2003),All this has laid a good foundation for the application and development of concrete confined with CFRP in China.On the basis of many collection and analysis of reports and articles at home and abroad which related to concrete columns confined with CFRP cloth, combined with CECS146-2003 ,GB50367-2006 and ACI Committee 440, We believe that there are several problems still need to be further research about concrete columns confined with CFRP cloth:1.A large number of experimental study on concrete columns confined with CFRP cloth has been carried out, there are a lot of test data available in the literatures at home and abroad, the analysis indicated that there were some obvious differences between scholars, both are based on the model of concrete cylinder strength confined with stirrup or empirical model which based on test results, the predicted strength of concrete cylinders confined with CFRP cloth has not been solved with unified understanding. Therefore, based on systematic analysis of existing results, we hope that the strength model and the constitutive model were given more reasonable.2.Available data are more concentrated on the mechanical properties study of reinforced concrete column confined with CFRP cloth, the research work rarely reported about the mechanical properties of high-strength concrete column confined with CFRP cloth.3.Most investigations have mainly concentrated on short columns. In contrast to the vast available database on short reinforced concrete columns, literature on slender columns is infrequent and limited. Whether the code in GB50367-2006 (the stability coefficient of RC concrete whose cylindrical column that slenderness ratio under 12 and rectangular column that slenderness ratio under 14 is not taken into account) is suitable to the reinforced concrete column wrapped with CFRP cloth, need further testing .Therefore, it is very important to study the stable bearing capacity of RC slender columns sufficiently confined by CFRP cloth in order to know mechanics character of them with great slenderness ratio.The corresponding theoretical analysis and experimental research work were carried out in the issues paper and main results are as follows:1. Based on collection and analysis of large amounts of experimental data about circular-section concrete columns confined by CFRP cloth in domestic and abroad,according to the understanding of the loading process of concrete column confined with CFRP well, to Core Strength f c/and the ratio of confinement stiffnessβj as the main variables ,we studied the values of the main parameters of problem of stress - strain equations.2.By the axial compression tests on a total of 19 high-strength concrete columns wrapped with CFRP cloth, the influence of shape section and different confinement ratio on the axial compressive strength and ductility is studied. The experimental results indicate: high-strength concrete columns wrapped with CFRP in increasing the bearing capacity and ductility of concrete columns is still valid, its effect on the improvement of ductility is much greater than its capacity, but still with a great deal of brittleness at failure.Based on collection and analysis of large amounts of experimental data about concrete columns confined by CFRP cloth in domestic and abroad,the calculation model of strength and ultimate strain are obtained by the regressive analysis of results. The model can be used to forecast the limit strength and deformation of high- strength concrete column confined with CFRP. This filled the design blank of high-strength concrete columns wrapped with CFRP cloth (GB50367-2006 is not given the limit deformation formula ).3.Axial compression tests on a total of 22 reinforced concrete slender columns wrapped with CFRP show that slenderness has more effect on the stable bearing capacity of CFRP-wrapped concrete column than that of reinforced concrete (RC) column. we discusses some factors including slenderness ratio, cross section and confinement ratio that affect stability coefficient.The test results show that slenderness ratio has more effect on the stable bearing capacity of CFRP-wrapped concrete column than that of reinforced concrete (RC) column. When slenderness ratio is less than 17.5, the stable bearing capacity of CFRP-wrapped concrete column is still 20% higher than that of RC column(confinement ratioξ=0.188). Axial compression tests on reinforced concrete slender columns wrapped with CFRP have shown that when the slenderness ratio is increased, the effect of retrofitting decline. For slender columns with same slenderness ratio, shape of cross section and confinement ratio of columns are main parameters which affect stability coefficient. In the case of same slenderness ratio, the stability coefficient of the reinforced concrete column wrapped with CFRP is much lower than RC column, the stronger CFRP wrapped concrete, the smaller stability coefficient. The code in GB50367-2006 (the stability coefficient of RC concrete whose cylindrical column that slenderness ratio under 12 and rectangular column that slenderness ratio under 12 is not taken into account) is not suitable to the reinforced concrete column wrapped with CFRP cloth, because CFRP cloth can only increase strength of concrete, not stiffness. The simplified formula for stability coefficient was summarized.4. In terms of the tangent modulus theory , the capacity-slenderness ratio curve in theory was calculated and compared with the experimental curve.5. This paper proposes the model that concrete and CFRP are seen as a composite material to analyze the specimens.Column specimens were successfully analyzed by ANSYS program, taking into account constitutive relationship of CFRP sufficiently confined concrete, failure criterion and initial imperfections. A parametric study was carried out to examine the main parameters affecting the stability coefficient of the reinforced concrete column wrapped with CFRP. For slender columns with same slenderness ratio, shape of cross section and confinement ratio of columns are main parameters which affect stability coefficient, the steel ratio of longitudinal reinforcement has little effect on it. The simplified formula was summarized for stability coefficient of the reinforced concrete column wrapped with CFRP.6. Based on "Strengthening Design Codes of Concrete Structures" (GB50367: 2006) and "Technical specification for strengthening concrete structures with carbon fiber reinforced polymer laminate" (CECS146: 2003), the design advice was proposed for axial compression concrete columns confined with CFRP, which can provide a reference for engineering designers.
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