Theoretical Study On Torsional Behavior Of CFS Strengthening Reinforced Concrete Box Beams Subjected To Combined Action Of Bending-shear-torsion

CFS(carbon fiber sheets) has been paid enough attention to strengthendifferent structures for its incomparable advantages over the otherstrengthening materials. But theoretical and experimental researches onCFS strengthening reinforced concrete members subjected to torsion havebeen rarely presented. Such information on CFS strengthening reinforcedconcrete members subjected to the compound action ofbending-shear-torsion has not been found in print. Based on thesephenomena and problems, A theoretical study of CFS strengtheningconcrete box beams through the model experiments of the CFSstrengthening concrete box beams subjected to compound action of bending,shear and torsion is made. Taken the actual strengthening engineering into account, this papermakes an analysis of the strengthening style of the box beams subjected tobending, shear and torsion, and suggests that different strengthening stylesshould be adopted according to different beams in order to achieve goodeconomic performance. Using the basic theories, the ultimate torsion strength was alsocalculated and it comes to a conclusion that the calculated values are biggerthan the experimental ones when using the variable-angle spatial trussmodel. Because of the diagonal concrete bars strengthened by CFS are intwo-dimensional compression, it is suggested that the softening coefficientof concrete should be increased by 1.25 while using the modifiedcompression field theory. The comparisons between the experiment and thetheory show a good agreement. So the method can be used for calculatingthe ultimate torsional strength. At the same time the method of nonlinearfinite element was also used to analyze the experimental beams.Furthermore, Against the experimental data, the results are comparedrespectively between the experiment and each theory, and the possibleproblems in experiment and theory are analyzed too. The experiment and all the theoretical analyses are of greatsignificance for actual rehabilitative projects, popularizing CFSstrengthening technique and providing useful experimental and theoreticaldata and methods for compiling corresponding regulations and norms.