| It is found in the investigation of the earthquake hazards that the brittle failure of RC columns in the buildings caused by the deficiency of ductility is one of the important reasons, which can bring the severe damages to the buildings. A new method for strengthening the columns by wrapping the CFRP sheets is becoming more and more popular in civil construction because its effectiveness for improving the shear capacity and the ductility of the RC columns and attracts more and more attention.In the present thesis, the calculation methods of the shear strength of the RC columns with circular and rectangular section by wrapping the CFRP sheets were summarized and analyzed. For the rectangular columns, seven methods proposed in the design codes, guidelines and literatures were summarized. Based on the compare between the calculation results and the test results of 33 columns, the reliability of the seven calculation methods and the contribution of the FRP to the shear strength were analyzed. The simple but reliable calculation method of the rectangular columns strengthened with wrapping CFRP sheets was proposed based on the study. The methods of the circular columns in three literatures were also analyzed.The important part of the thesis was the experimental study on the seismic capacity of the circular RC columns with wrapped CFRP sheets under high axial ratios. According to the test data, the ductility and the hysteresis consuming-energy capacity was analyzed, as well as the shear and flexural capacity. At the same time, the CFRP amount and the axial ratios, the parameters influencing the ductility of the columns, were studied. The strain distribution in the CFRP sheets in the vertical direction and the transversal direction was analyzed, and it was found that the maximum CFRP strain when the column reached the ultimate state was related with the CFRP amount and the axial ratio. With the effect strain of CFRP ?f,e when the column reached the ultimate state, the concept of equivalent transversal reinforcement index of steel hoops ??v was presented, and the calculation method of ?v was proposed. Based on the analysis of the experimental results, the conclusion was drawn as follows: if the equivalent transversal reinforcement index ?v of the RC column strengthened with wrapped CFRP sheets no less than the limitation value provided by Chinese seismic design code for building RC columns, the seismic capacity of the columns could meet the demand of the ductility. |
