Title:thermal-mechanical Coupling Analysis Of Concrete Structure Construction In Subway Station

With the continuous expansion of the city,more and more cities have carried out the construction of underground rail transit.Metro stations are large-volume concrete structures,which are prone to cracking and water seepage,which brings hidden dangers to the safe operation of the subway.The key factors affecting concrete cracking are temperature changes and temperature stresses.Concrete temperature cracks often originate from temperature changes during construction or operation,and the structure will produce corresponding deformation and stress under the action of internal and external temperature differences and constraints,and when the structural stress strain exceeds the material limit,the corresponding temperature cracks will be generated.At present,the study of concrete temperature-stress field is mostly sequential coupling method,and there is little research on underground large-volume concrete structure,and the joint effect of load factors and non-load factors is rarely considered,so this paper uses the temperature-stress field complete coupling and damage analysis method to study the temperature stress of concrete structure of subway station during construction,and the main work and conclusions are as follows:1.The compressive strength,tensile strength and adiabatic temperature rise tests of the C35 concrete used in this paper were carried out,and the relevant calculation parameters were obtained,and the temperature-stress field coupling analysis method was verified by the concrete plate model,which could be used for the temperature stress analysis of large-volume concrete.2.The three-dimensional model of the standard section of the metro station was established by using the finite element thermal complete coupling and damage analysis method to carry out numerical simulation analysis(considering the construction process),and the temperature field,stress field,displacement field and damage distribution during the construction period were analyzed.The results show that the floor plate,roof plate and side wall concrete reach the maximum temperature about 30-50h after pouring,and the temperature trend with time rises first and then decreases.The stress growth law is faster in the early stage,and then the growth is slow,which is consistent with the temperature change law;The side walls are affected by the earth pressure of the surrounding soil,which is the result of a combination of temperature stress and external load.The floor is subjected to load at the same time,the temperature stress is greater than that of the roof plate and the side wall,and the maximum principal stress of each component exceeds the tensile strength of C35 concrete at the same age.In the concrete pouring process,the damage is mainly tensile damage,and the damage value is increasing over time.By comparison,it can be obtained that the stress concentration locations such as the bottom edge position of the side wall and the junction of the column plate are the areas most prone to cracking of concrete,and effective measures should be focused on and taken during the construction period.3.The key influencing factors of cracking of concrete structures in metro stations were analyzed,and the distribution characteristics and variation laws of temperature-stress fields of concrete structures in metro stations under different pouring temperatures,convection heat transfer coefficients of concrete surfaces considering thermal insulation measures,different ambient temperatures and different linear expansion coefficients were discussed,and measures to prevent or reduce cracks in concrete structures in metro stations were proposed.The calculation results show that:(1)The pouring temperature has obvious influence on the internal temperature of the concrete structure,and the effect on the surface temperature of the concrete structure is small,and the stress of the concrete structure increases by 0.1MPa for every 1℃increase in the pouring temperature,and the stress growth accelerates significantly with the increase of the pouring temperature.(2)The use of insulation materials with small convective heat transfer coefficient,the maximum temperature occurrence time is later than that of insulation materials with large convective heat transfer coefficient,the smaller the convective heat transfer coefficient,the lower the stress of the concrete structure.(3)The change of ambient temperature has obvious effects on the surface temperature of concrete structures,and the impact of ambient temperature changes on the stress of concrete structures is also obvious,and the maximum principal stress is reduced by 22%when the ambient temperature is 30℃than when the ambient temperature is 15℃.(4)The change of linear expansion coefficient has almost no effect on temperature and has a significant effect on stress.The stress and the coefficient of linear expansion of concrete are approximately a function of one,and the temperature stress is reduced accordingly with a smaller coefficient of linear expansion.This achievement can further improve the durability of concrete in subway engineering,provide a certain reference for the construction and design of subway stations,and reduce the maintenance cost of subway during construction and use.