Study On The Influence Of Time-varying Thermal Expansion Coefficient On Numerical Simulation Of Concrete

After nearly 200 years of development,concrete has become the most widely used building materials in the world.With the deepening of research,the performance of concrete materials and the construction technology of structure have been improved continuously.However,the problem of structural cracks has not been well solved all the time.Long-term engineering experience shows that adjusting construction measures according to simulation results is one of effective methods to control structural cracks.Therefore,it is necessary to understand the thermal and mechanical properties of concrete accurately and apply them reasonably to the numerical simulation of structure.The thermal expansion coefficient of concrete is an important parameter in the simulation of temperature-stress.For a long time,people always regard it as a constant in the simulation,ignoring the correlation between its change and age.In order to improve our understanding about the evolution of concrete and perfect the simulation process of temperature stress.In this paper,the time-varying characteristics about the thermal expansion coefficient of concrete are studied.Further,its influence on temperature-stress simulation is studied.Consequently,in this paper,the thermal expansion coefficient of C₁₈₀36 concrete which used in Dagangshan arch dam was taken as the main body of study.We used the raw materials and mix ratio of the C₁₈₀36 concrete to carry out the test.Then,the numerical simulation research based on the test results is carried out.Firstly,two groups of temperature-stress tests under different temperature curing modes were designed.Then,the thermal expansion coefficient of concrete was calculated based on equivalent-age theory and hydration degree theory respectively,and its time-varying model was established according to the calculated values.Subsequently,the Autogenous volume deformation was separated from the total strain based on the measured temperature and total strain data.Then,the numerical simulation of temperature-stress test was carried out to verify the accuracy of the time-varying thermal expansion coefficient model.In the end,the time-varying thermal expansion coefficient was substituted for the simulation of the actual project Dagangshan arch dam,and the influence of time-varying thermal expansion coefficient on temperature-stress simulation was studied.The experimental results show that the thermal expansion coefficient of concrete is correlated with its hydration process,and it varies greatly in the early age.The simulation results of temperature-stress test show that the time-varying thermal expansion coefficient model is accurate and reliable.It is necessary to consider the time-varying thermal expansion coefficient in temperature-stress simulation.The simulation results of Dagangshan arch dam show that the time-varying thermal expansion coefficient has different influence on different restricted area in the simulation of the actual project.The simulated stress level calculated by considering the time-varying effect was higher than that of the traditional method,especially for the concrete with fast temperature drop rate at early age due to water flow.It is safer to carry out crack prevention design according to the new method.