An Experimental Study Of Damaged Reinforced Concrete Beams Strengthened With Pre-stressed CFRP Sheets

Due to the deficiency of design and construction or the change of function, the concrete structure are found be damaged and in need of strengthening or rehabilitation. Strengthening RC member by bonding CFRP sheets externally is an important technique. Thirty four damaged beams strengthened with epoxy-bonded carbon fiber reinforced plastic (CFRP) sheets are experimentally investigated. The flexural performance and shear performance of the beams strengthened with CFRP sheets and the flexural performance of the beams strengthened with pre-stressed CFRP sheets are studied. On the basis of experiments, the methods for calculating the ultimate capacity and stiffness, width of crack of the repaired beams by (pre-stressed) CFRP are studied.1,The repaired beams with different reinforcement ratio, amount of CFRP, initial load are tested and some beams strengthened with pre-stressed CFRP using the installation made by ourselves. By measuring the diagnostic strength, deflection, width of cracks and stain of the concrete, reinforced bars, CFRP sheets of the repaired beams, observing the failure modes, the flexural performance of the repair beams is studied.2,There are four failure modes observed in the examination: rupture of CFRP sheets, crush of concrete, de-bond failure of concrete, de-bond failure of plastic. The failure mechanism is analyzed and some parameters including amount of the CFRP sheets, reinforced ratio, method of anchor, pre-stress and initial load are considered and the main rules are summarized. The roles of the crack load, yield load and ultimate load of the repaired beams change with the parameters above are detailed studied and the emphasis is the effect of the pre-stress and initial load.3,The rules of the deflection and the crack of the repaired beams are studied and the effect of the parameters on the deflection and width of crack, space between crack are analyzed. The method of improve the performance of the deflection and crack is proposed.4,The finally strain of CFRP sheets has been measured and the finally strain that the CFRP can reach to on different failure modes is analyzed. Some suggests about the admit strain of CFRP are proposed.5,Based on experimental research and flexural capacity calculation theory, a method for calculating the yield capacity and the ultimate capacity of member strengthened with CFRP sheets is proposed. The effect of prestressing force and initial load are considered when the formulas are put forward.6,On the basis of analyzing the calculation theory of section stiffness of Reinforced concrete beams, a method for calculating the section stiffness of the beams strengthened with pre-stressed CFRP sheets is proposed. The effect of prestressing force and initial load are considered when the formulas are put forward. On the basis of experimental research and analyzing the calculation theory of crack of Reinforced concrete beams, a method for calculating the width of crack of the beams strengthened with CFRP sheets is proposed. It is testified that the formulas are agree with the result of experiments and the formulas can be available for reference in design.7,Adopting the way of numerical value analysis, the whole development process of the repaired beams is studied and the analysis result is agree with experiments. The calculational load-deflection curves are agreed with measured curves.8,The shear capacity of reinforced concrete beams with epoxy-bonded carbon fiber reinforced plastic (CFRP) sheets has been experimentally investigated. The shear capacity and parameters influencing the shear capacity of RC beams strengthened are analyzed. A formula for the shear capacity based on statistical comparison is proposed. It is found that the calculated results are in a good agreement with that of the test and the formula can reflect the effect of parameters of the shear-span ratio, the CFRP amount and the strength of the concrete.9,Based experimental and academic research, the method for calculating the capacity of member strengthened with CFRP sheets and pre-stressed CFRP sheets is proposed, and some suggests about the construction techniques are proposed. These formulas and suggests provides background materials to corresponding engineering construction code.Finally, this paper summarizes the ideas and raises some problems need to be further researched.