Experiment And Numerical Simulation Of Concrete Mechanics Under High Temperatureenvironment

Since the western development strategy,there have been more and more high-temperature diversion tunnel projects in the western region of China.However,the high-temperature environment in the tunnel not only brings great trouble to the construction of the project,but also brings great safety hazards to the tunnel project.In order to provide certain theoretical guidance for the construction of the actual project.In this paper,five kinds of temperature conditions are set,and targeted laboratory tests are carried out.Combined with the non-contact full-field strain system,the mechanical properties and strain variation rules of concrete under different temperatures were investigated.A corresponding thermodynamic coupling model is constructed based on the particle flow method,and the simulation effect of the thermodynamic coupling model is verified by comparing the numerical simulation results of discrete elements with the results of physical experiments.Then the general law and the mesoscopic mechanism of the mechanical properties of concrete under high temperature environment are analyzed by using the particle flow thermodynamic coupling model.The main research results are as follows:(1)Based on the design of five temperature conditions,a test device that can be used with the pressure testing machine to load concrete samples at high temperature is developed.The synchronous test of non-contact full-field strain system during high-temperature sample loading is realized.(2)Through the high temperature loading test of concrete,it is found that the high temperature environment has obvious influence on the peak strength,elastic modulus and peak strain of concrete.The peak stress and elastic modulus of concrete decrease with the increase of temperature,while the peak strain of concrete increases with the increase of temperature.(3)The evolution characteristics of the strain cloud map at different temperatures can reflect the reason of the change of the macroscopic properties of concrete.Compared with the normal temperature sample,the tensile strain and compressive strain components of the sample will increase under the action of high temperature,but there is little change at 40℃,60℃ and 80℃.The shear strain component tends to increase with the increase of temperature.The components of tensile strain,compressive strain and shear strain continued to increase before the peak of uniaxial test,and the components of tensile strain and compressive strain increased faster after the peak.(4)The high temperature damage law of concrete is further analyzed and studied by establishing the particle flow thermodynamic coupling model,and the correctness of the model is verified by experiments.Furthermore,the verified model is used to reveal from the microscopic perspective that the thermal stress and micro-cracks in concrete due to the different expansion coefficients of mortar and aggregate are the microscopic mechanism that leads to the peak strength and the attenuation of elastic modulus of samples.