Flexural Behavior And Calculation Method Of Reinforced Concrete Short Beam Strengthened By CFRP Sheet

Carbon fiber reinforced polymer(CFRP)is widely used in concrete structure strengthening and retrofitting because of its superior performance.The reinforced concrete(RC)short beam has large bearing capacity and is widely used in construction engineering,water conservancy project,port engineering,traffic and municipal engineering,etc.The flexural tests on 11 CFRP strengthened RC short beams were carried out to investigate the effects of span-depth ratio,layers of CFRP sheet,concrete strength and reinforcement ratio on failure mode,ultimate load,strain of concrete and reinforcement,CFRP strain,moment-curvature curve,load-deflection curve,load-angle curve and cracks of RC short beam strengthened by CFRP sheet.Calculation methods on flexural capacity,flexural stiffness and crack width of RC short beams strengthened by CFRP sheet were established.The main contents are presented as follows:(1)The influences of span-depth ratio,reinforcement ratio and amount of CFRP sheet on ultimate load of RC beams were analyzed.The results show that: the failure modes of RC beams strengthened by CFRP sheet included CFRP sheet fracture and concrete crushing;with the decrease of span-depth ratio,the ultimate load of RC beams strengthened by CFRP sheet improved significantly;with the increase of reinforcement ratio and amount of CFRP sheet,the ultimate load of RC short beams also improved significantly.According to the test results in this paper and other literature,the calculation method on flexural capacity of RC short beam strengthened by CFRP sheet,which considered the influence of span-depth ratio,was proposed.the method could also be used to calculate flexural capacity of RC shallow beam strengthened by CFRP sheet.(2)The influence of span-depth ratio on flexural stiffness of RC short beams strengthened by CFRP sheet was analysed.The results show that: moment-stiffness curve varies with different span-depth ratio.Based on the stiffness theory of concrete beam,the calculation model for predicting the flexural stiffness of RC short beam strengthened by CFRP sheet in the whole test process,which considered the influence of span-depth ratio,was proposed.On this basis,considering the effect of shear deformation on the midspan deflection of short beams,an equivalent flexural stiffness calculation model was proposed to accurately calculate the midspan deflection of RC short beams strengthened by CFRP sheet.(3)The effect of span-depth ratio on cracking load and crack width of RC short beams strengthened by CFRP sheet was analyzed.The results show that:with the decrease of the span-depth ratio,the cracking load of CFRP strengthened RC beams significantly increased;when the ratio of normal using load to yield load was the same,with the increase of span-depth ratio,the crack width of RC short beam strengthened by CFRP sheet decreased.Based on the theory of concrete cracking,the formulas for predicting cracking moment,average crack spacing,reinforcement stress and crack width of RC short beams strengthened by CFRP sheet were proposed.These formulas considered the effects of CFRP sheet and span-depth ratio.