A New Reinforced Concrete Fiber Beam-column Element Model Considering Bond-slip Effect

The fiber beam-column element model is between the micro(solid)model and the macro(bar)model.It can take into account both the simulation accuracy and the calculation efficiency of the structure.It can effectively simulate the nonlinear mechanical behavior of structural members subjected to space stress which contain compression,bending and shear force,especially the effect of bending-shear coupling effect.However,at present,the influence of bending-shear coupling effect on simulation accuracy is mostly considered in fiber model based on multi-dimensional constitutive relations of materials,and the process of stiffness updating is more complex.In addition,the bond slip effect between reinforcement and surrounding concrete is neglected,which leads to the distortion of the final simulation results.In order to improve the simulation accuracy of the fiber beam-column element model in the nonlinear stage on the premise of considering the computational efficiency,a new reinforced concrete fiber beam-column element model considering the bending-shear coupling and bond slip effect is presented in this paper.The specific works are as follows:The fiber model considering bending-shear coupling effect which based on uniaxial constitutive model of material.The shear effect of section is considered by combining Timoshenko beam theory with the classical fiber beam-column element model.The additional bending displacement generated by transverse shear deformation on the bending stiffness of section is introduced,so the coupling effect of bending and shear and the indirect effect of shear deformation on the axial deformation are considered.The fiber model considering the coupling effect of bending and shear based on uniaxial const itutive model of material,which is used to analyze the elastoplastic calculation of beam members,and the simulation results are compared with that of the current finite element model considering shear effect and bending-shear coupling effect,which verifies that the proposed fiber model has high simulation accuracy.Simplified simulation methods for bond slip effect of fiber model.Based on the bond slip strain of reinforcement,two methods considering the bond slip effect are proposed.One is to keep the constitutive model of reinforcement unchanged,according to the bond slip constitutive model,the slip strain of reinforcement is directly introduced to determine the corresponding tangent modulus and shear modulus.Considering that this method will increase the amount of calculation in each iteration process and reduce the calculation efficiency of the structure.The bond slip effect is indirectly considered by modifying the stress and strain values at the yield point and the limit point of the constitutive model of reinforcement.By eatablishing the comparative models,the influence of steel slip on the simulation accuracy of the model is analyzed.And it is verified that the method of considering bond slip effect in the modified consititutive model of reinforcement has high simulation accuracy and computational efficiency.Verification of fiber model by pseudo static analysis.Based on the proposed fiber model considering bending-shear coupling effect and bond slip effect,the horizontal load-displacement hysteresis curves and skeleton curves are obtained by pseudo static analysis.And comparing the simulation results with that of the existing fiber model and the classical fiber model in terms of bearing capacity,loading and unloading stiffness,it is found that the fiber model in this paper has good mechanical properties.The problems such as large calculation amount,difficulty of convergence and complexity of the existing fiber model have been solved.And the superiority of the new fiber model in the simulation accuracy and calculation efficiency has been further verified.