| The new-to-old concrete interface can be divided into two types: the interface with anchor bar and the interface without anchor bar.There are two types of calculation methods for the shear strength of the existing new-to-old concrete interface without anchor bar: considering normal stress and without considering normal stress.These methods not only have the problems of insufficient theoretical basis and need to improve the calculation accuracy,but also the unified calculation formula that can consider normal stress and zero normal stress is rarely reported.The calculation formulas for the shear strength of the new-to-old concrete interface with anchor bar are mostly based on the shear friction theory or fitting the test data,and the design codes of concrete structures in different countries also give their own formulas for calculating the shear strength.But these methods are either too conservative or lead to structural insecurity.Therefore,firstly,based on the three-dimensional energy yield criterion of concrete materials,the theoretical calculation formula for the shear strength of the new-to-old concrete interface without anchor bar is derived.By introducing the comprehensive influence coefficient of the normal stress of interface and the surface roughness of the old concrete,based on the existing shear test data and using three-dimensional curve fitting technology to modify the theoretical formula.The unified calculation formula of shear strength of the new-to-old concrete interface without anchor bar is obtained.And,the validity of the calculation formula is verified by the existing test data.Then,according to the stress characteristics of the new-to-old concrete interface with anchor bar,a spring-friction block model of interface shear force is established.And the shear force transfer mechanism of the whole process of joints is thoroughly analyzed.The shear bearing capacity of new-to-old concrete interface with anchor bar can be divided into four parts: the bonding force of the concrete,the occlusal force of groove,pin bolt force of anchor bars and the friction force,and the calculation formula for the shear bond strength of the new-to-old concrete interface with anchor bar is proposed.Meanwhile,the validity of the calculation formula is verified by the existing test data.Finally,referring to the existing numerical simulation methods and shear test results of the new-to-old concrete interface,the cohesive model in ABAQUS is used to establish the finite element model of the new-to-old concrete interface to simulate the shear bonding performance of the interface.The curve equation of the shear bond-slip constitutive model of the new-to-old concrete interface is established,and the constitutive model is verified with test data.Through the above work,the conclusions of the paper are as follows:(1)The unified calculation method for shear strength of new-to-old concrete interface without anchor bar proposed in this paper can be applied to compression(tension)shear composite members as well as to pure shear members.The theoretical basis is sufficient,the calculation is simple,but the calculation accuracy is better than the existing calculation methods.(2)The calculation results of the calculation formula for the shear bond strength of the newto-old concrete interface with anchor bar proposed in this paper are the most consistent with the test results,and the degree of dispersion is the lowest.(3)The finite element analysis results of the shear performance of the new-to-old concrete interface show that the shear stress-slip curve and the shear bearing capacity of the specimens obtained by the numerical simulation are consistent with the test results.The cohesive model can accurately simulate the bond-slip behavior of the interface.(4)The bond-slip cinctitutive model proposed in this paper is in good agreement with the test results,and it can accurately predict the maximum shear stress and the corresponding slip value of the new-to-old concrete interface with anchor bar. |
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