Study On Mechanical Performance And Construction Simulation Of Large-span Ice Shells

Ice structure is a kind of architectural form with ice as the primary stressed material,which has the advantages of a long history of development,green environmental protection,and high ornamental value.It not only plays a huge role in ice and snow tourism,but also has potential application in polar and even outer space exploration.The conventional ice structure is mainly constructed by natural ice masonry.Owing to natural ice’s weak bearing capacity and the relatively backward masonry construction method,the scale and shape of traditional ice structures are limited.In recent years,scholars have actively explored the application of modern construction technology in ice and snow structures,and proposed a large-span ice shell structure using inflatable membrane as temporary formwork,combined with water-fiber mixed solution spraying and freezing technique.Compared with the traditional ice structure,this novel ice shell structure has more reasonable mechanical behavior and richer shapes,representing the development direction of modern ice and snow structures.Based on the above background,this paper intends to systematically study the large-span ice shell structures from two aspects of mechanical performance and construction simulation analysis,and then establish the corresponding design and construction analysis theory to promote the engineering application of novel ice shell structures in China.The main work includes the following aspects:(1)The thermo-mechanical damage constitutive model for PFRI is established based on damage mechanics and material tests.A “two-stage” thermo-mechanical damage constitutive model is proposed regarding fiber-reinforced ice as a quasi-brittle material.In the early loading stage,the thermo-elastic equation is established by introducing temperature variables.After the material interface is damaged,the damage evolution model for fiber-reinforced ice is deduced by introducing the cohesive crack model in damage mechanics,which realizes the numerical simulation from material damage to fracture.The fracture energy of ice material is measured based on the three-point bending notch beam tests.Through the self-developed damage subroutine and typical test,the selection of damage softening curves and grid sensitivity suitable for fiber-reinforced ice are studied.The accuracy and applicability of the thermo-mechanical damage model are verified,which lays a theoretical foundation for the subsequent study of large-span ice shell structures’ damage mode and failure mechanism.(2)A refined structural analysis method considering the influence of solar radiation is established,and the failure mechanism of ice shells under thermo-mechanical coupling is revealed.A non-uniform temperature field analysis method considering solar radiation is established,and the thermo-mechanical coupling analysis method considering continuous temperature variation is proposed,which realizes the elaborate simulation of the mechanical performance of ice shell structure.Subsequently,combined with typical examples,the ultimate bearing capacity of ice shell structure considering material and geometric nonlinearity is studied,the damage mode and failure mechanism under different load forms and environmental temperature are analyzed.Finally,the evolution laws of non-uniform temperature field and thermo-mechanical damage for large-span ice shell structure under actual service environment are studied.(3)The shape control method of inflatable formwork that realizes the design requirements of complex-shaped ice shells is introduced.Unlike the design of conventional inflatable membranes,the inflatable formwork of ice shell takes the “shape-matching” as the primary goal,and the mechanical performance only needs to satisfy the construction load.Hence,a shape control method for complex-shaped inflatable formworks is proposed.Through the rapid inflatable simulation and parameter optimization,the inflatable membrane closest to the design shape of ice shell can be obtained,which is then utilized as the temporary construction formwork.Considering the complexity of the inflatable formwork optimization,several measures to improve the calculation accuracy and convergence efficiency are proposed.Finally,the effectiveness and superiority of the shape control method for complex-shaped ice shells construction are demonstrated by numerical examples.(4)The spray construction simulation considering the coupling process of water-film flowing and layer-by-layer freezing is carried out.The spray construction of ice shell structure involves liquid flow and material phase transition,which is a typical multi-physical field coupling problem Through the analysis and appropriate simplification of the construction process,it is decoupled into water-film flowing and layer-by-layer freezing process.The mass conservation model describing the water-film flowing and the heat balance model of freezing into ice are established respectively.Through numerical examples,the interaction laws of construction time,water demand and construction quality are discussed,and the effectiveness and application value of spray construction simulation method are further expounded.(5)An analysis system for ice shell structures is developed and successfully applied to several practical projects.By integrating the approaches in the previous chapters,an analysis system for large-span ice-shell structures,named Rhino Igloo,is developed based on the Rhino-Grasshopper parametric platform to realize the rapid design and evaluation of complex-shaped ice-shell structures.Several large-span ice shell projects over10.0 m span since 2016 are summarized.The integrated analysis system’s effectiveness and engineering application value are explored by taking the ice shell of “Ice-dreamland” built-in 2020 as a typical case.