Research On Temperature Fields And Crack Control Of Mass Concret In Ion Hospital Structure

With the continuous development of proton and heavy ion technology,all countries in the world are competing to develop the development of proton and heavy ion treatment equipment and the construction of related institutions,and vigorously promote the proton and heavy ion radiotherapy technology and clinical research.Due to the strong penetration of high-energy proton flow radiation generated in the treatment process,the radiation needs to be shielded by concrete with sufficient density and thickness,resulting in the large volume and complex shape of concrete members in the ion hospital,and the requirement for crack control is higher than that of other mass concrete buildings.Therefore,this paper takes Hefei Ion Medical Center as the research object,establishes a complete set of finite element simulation methods,and puts forward suggestions and optimization for construction technology.The main contents of this paper are as follows :(1)According to the structural characteristics of the ion hospital,the key and difficult points in the construction measures were analyzed,including the layered and segmented pouring of the wall plate,the adjustment of the concrete mix ratio,the progressive continuous pouring and the maintenance measures.The on-site temperature monitoring scheme was described,and the temperature data were analyzed to verify whether the internal temperature appreciation,cooling rate,temperature difference between internal and surface of concrete and temperature difference between concrete surface and environment exceed the standard value.(2)Starting from the concrete material parameters,the double exponential function model established according to the existing literature on the hydration heat of concrete,fitting elastic modulus formula by experimental data.Considering the influence of Mg O expansive agent and concrete shrinkage,the expansion coefficient of concrete was corrected and the equivalent thermal expansion coefficient was proposed.On the platform of ABAQUS secondary development,the subroutine HETVAL,USDFLD and UEXPAN were written by FORTRAN to realize the hydration heat,elastic modulus and thermal expansion coefficient function of concrete.The validity of the subroutine and the feasibility of ABAQUS sequential thermal-mechanical coupling were verified by simulating the temperature field and stress field of the hospital field test block.(3)In order to obtain the distribution law of temperature field and stress field of the overall structure of the hospital,the finite element analysis was carried out.The temperature field results showed that the temperature simulation value was in good agreement with the monitoring value.When the wall thickness was large,the internal peak temperature was close,and was less affected by the boundary conditions.The ‘ life and death unit ’ can well realized the layered and segmented pouring of the structure.According to the simulation results of stress field,the most unfavorable position of the structure was pointed out.The simulation results showed that the peak stress generally appeared on the concrete surface and the interface of two pouring.At the same time,there was no penetrating crack in the whole maintenance process,which proved the reliability of hospital construction measures.(4)In order to further discuss the influence of structural delamination thickness and segmentation method on temperature field and stress field,the parameter variation schemes of plate delamination and wall segmentation were designed,and the finite element simulation was carried out.At the same time,the influence of mold temperature and cement content on the peak temperature of the structure was analyzed.