Numerical Simulation Study On Fire Case And Construction Process Of Dome Structure Of Concrete Full Containment Tank

The concrete full containment tank is one of the important equipment for storing liquefied natural gas.With the continuous development of concrete full containment tanks in the direction of large-scale,the difficulties of design and construction are also increasing.The design and construction technology of the dome structure of the concrete full containment tank is the key and difficulty in the construction of the concrete full containment tank project.The dome structure has the characteristics of large self-weight and large span.It is of great practical significance to study the safety of the dome structure to ensure the safety of the concrete full containment tank and promote the development of the natural gas industry.This paper takes the dome structure of a typical large-scale LNG concrete full containment tank with a volume of 160,000 cubic meters as the research object and carries out numerical simulation research on its fire cases and construction process.The main research contents and conclusions are as follows:An equivalent calculation method to calculate the internal temperature field of the concrete full containment tank is established.Based on the heat exchange between the concrete full containment tank and the internal and external environment,the heat transfer balance equations of the concrete full containment tank are established.The internal temperature field of the concrete full containment tank is approximately equivalent to a one-dimensional heat conduction problem,and the approximate solution of the one-dimensional heat conduction equation is used to replace the solution of the internal temperature field.The heat exchange between the internal temperature field and the concrete outer tank is equivalent to the convective heat transfer boundary,and the simplified calculation of the internal temperature field of the concrete full containment tank is realized.The effectiveness of the calculation method is verified by comparing it with the results of fire experimental.The influence of fire on the dome structure is studied.Based on the finite element analysis of three fire scenarios,i.e.point source fire,semi-enclosed fire and fully enclosed fire on the dome structure,the temperature,deformation,stress and failure characteristics of the dome structure under fire are studied.The results show that: under the action of fire,the dome structure shows the temperature distribution law of high temperature on the outside and relatively low temperature on the inside;the dome structure shows the characteristics of compression in the high-temperature regions and tension in the relatively low-temperature regions;Under the constraints of the structure itself,the temperature difference is an important factor causing the temperature stress.A large area of concrete on the inside of the dome structure will suffer from tensile failure,and the steel dome will become the main bearing structure on the inside of the dome structure.Compared with concrete dome alone,steel dome can increase the height of concrete dome compression zone,and effectively improve the bearing capacity of the dome structure.The influence of different pouring schemes on the dome structure is analyzed.Based on the finite element analysis of three kinds of pouring schemes,i.e.integral pouring scheme,separate ring pouring scheme and separate layer pouring scheme of the dome structure,the temperature and stress characteristics of the crack-prone areas at the edge of the dome structure were studied.The results show that: under the action of the heat of hydration,the early-age concrete has experienced heating and cooling stages and has undergone a change process from compression to tension with the temperature change.Comparing each pouring scheme,it can be seen that: in the integral pouring scheme and separate ring pouring scheme,the concrete at the edge of the dome structure has the risk of cracking during the pressure relief stage;in the separate layer pouring scheme,the stress state of the concrete at the edge of the dome structure is always in the safe range during construction.In addition,the influence of pressure holding time and value on the dome structure is also studied,which provides a reference for further optimizing the pouring scheme of the dome structure.