Research On Shear Strength Of Reinforced Concrete Beams Based On Elastoplastic Stress Field Theory

Reinforced concrete beams are important bending members in the structure,they not only bear bending moments but also withstand shear forces.At present,the research on the bending resistance of reinforced concrete beams is very sufficient,the analysis of the mechanical behavior based on the plane section hypothesis can accurately estimate the bending capacity.However,the influencing factors of the shear resistance are numerous and their interaction is very complex.On the basis of a large number of experiments,the academia has put forward various theories to calculate the shear capacity of reinforced concrete beams,but so far it has not drawn a unified computing theory and model for shear failure mechanism to better predict the shear performance of structures.Therefore,it is necessary to propose a new shear calculation method to accurately predict the shear capacity of the member.Nowadays,the rapid development of nonlinear finite element method has injected a new vitality into the analysis of the shear capacity of reinforced concrete structures.Nevertheless,when the nonlinear finite element software is used,the calculation results will be significantly different due to the adoption of different constitutive models for concrete and reinforcement.Based on the above research background,this paper systematically studies the elastoplastic stress field theory(EPSF)proposed by scholar Fernández Ruiz and Muttoni.This method is based on the theory of rigid plastic stress field.In contrast,it uses more reasonable assumptions to consider the influence of cracked concrete on the components.It considers all potential bearing mechanisms in the limit state to give an exact solution based on the limit analysis.The method is implemented by a two-dimensional nonlinear finite element program ICONC based on JAVA.Based on the elastoplastic constitutive relation of the material,the program calculates the stress of concrete and steel bar by applying deformation,and repeatedly obtains the stress field of each load stage,and finally obtains the simulation result which is consistent with the measured value.ICONC needs to be meshed by programming.In this paper,three meshing programs are developed using PYTHON,which are used for reinforced concrete slabs under the uniform load,reinforced concrete beams under single point loading,and reinforced concrete beams under two points concentrated loading.This paper focuses on the analysis of the influencing factors of EPSF modeling.The influence ofthe size and shape of finite element mesh is studied on the stability of the results.The influence of the iterative number is studied on the accuracy of EPSF model,and the corresponding modeling method is proposed.According to the experimental data of 9reinforced concrete beams in our research group and other reinforced concrete beams,the simulation values are compared with the experimental values to verify the accuracy of the method in analyzing the shear behavior of reinforced concrete beams.At the same time,compared to the ABAQUS simulation results,the results show that the simulation results of this method are better than ABAQUS.Finally,the experimental data of 70 reinforced concrete beams subjected to concentrated loads at home and abroad are summarized.All the collected beams undergo shear failure.The shear capacity of those beams are calculated by the use of the US and Chinese design code,and ICONC modeling analysis.The results from those three methods are compared with the experimental values,which demonstrates the accuracy and generality of the solution using the elastoplastic stress field.