Optimized Schemes On Shear Strengthening Of Deep-T-Cross-section RC Beam With Near Surface Mounted CFRP Bars

The deep T-cross section RC beam structures are widely used in the transition layer of high-rise structure,the side wall of large shallow storehouse and the load-bearing components of high-speed railway,bridge and Marine construction because of large bearing capacity,high construction efficiency and economic benefits.Due to the unreasonable design theory and selected calculation model,the long service time of the structures,the bad external environment and the change of the use function,etc.,the bearing capacity of the structures can not meet the function.Therefore,how to scientifically master the distribution of the internal force flow of the deep T-cross section RC beam and develop appropriate reinforcement methods to improve the shear capacity of the current deep T-cross section RC beams has become a research hotspot in the engineering fields.Firstly,the 'strut-and-tie' model is selected to characterize the mechanical calculation model of deep T-cross section RC beams by widely studying and comparing the development status,the relevant specifications,the technical specifications,the transformation and reinforcement from domestic and abroad of the field in concrete structures design,In view of the special structure form of the deep T-cross section RC beam and the deformation characteristics after bearing load.On the condition of maintaining the same ratio of CFRP bars and epoxy adhesive,the tensile strength of CFRP bars with different sections are tested and compared through standard tensile tests.Finally,selecte CFRP bars that made of 32 strands of single silk as reinforcement bars for the deep T-cross section RC beams.The double-shear drawing tests piece with symmetrical embedded CFRP bars are used to study the bond failure mechanism,interfacial stress transfer and slip law of CFRP bars-concrete interface,results reflect that the bond-slip constitutive model between structures and CFRP bar are established and the effective embed length of CFRP bars are determined.Secondly,using ANSYS numerical simulation platform to analyze the distribution law of internal force flow and strain of unreinforced original deep T-cross section RC beams under three-point bending load.The main stress traces on the surface of the deep T-cross section RC beams are drawn,which verified that the selected 'strut-and-tie' model conforms to the stress characteristics of the deep T-cross section RC beams.According to the pull-out tests and simulation results of original deep T-cross section RC beam,the section size,effective embedded length and positions of CFRP bars are determined.In combination with the actual reinforcement engineerings,four reinforcement schemes,such as one simple reinforcement form and other three optimized reinforcement forms are developed,meanwhile,the evaluated reinforcement effects of the deep T-cross section RC beams under the corresponding working conditions are simulated.Finally,two reinforcement schemes of simple reinforcement and optimal reinforcement of deep T-cross section RC beams are selected by the comparison of parameters such as mid-span deflections and shear bearing capacity of the beam based on the results of numerical simulation,the corresponding experimental deep T-cross section RC beams are designed and produced at the same time,which are carried out to verify the two reinforcement schemes' effects.In the end,the experimental results show that the simple reinforcement scheme and the optimized reinforcement scheme respectively increased the shear capacity of the deep T-cross section RC beams by 45% and 65%.The results of theoretical calculation,numerical simulation and experimental verification show high consistency,which demonstrate the selected 'strut-and-tie' model conforms to the stress characteristics of deep T-cross section RC beam under three-point bending load.The results also reveal the shear strengthening mechanism of deep T-cross section RC beam and verify the feasibility and practicability of the reinforcement schemes.Based on the above results,the author applies for an invention patent on the methods of shear reinforcement of deep beams,which is expected to have practical guiding significance for practical reinforcement engineerings.