Dynamic Damage Mechanisms Of Single Layer Latticed Shells Under Strong Earthquakes

Single layer latticed shell, which has the characteristics and excellences of both member structure and shell structure, is widely used in our country. Our country has a high incidence of earthquake, and a great number of landmark constructions with the structural type of single layer latticed shell locate on the strong earthquake areas. Currently general beam element of finite element analysis program is used to simulate the structural member and rigid connection model is used to simulate the structural joint when study the anti earthquake behaviors of single layer latticed shells. By this method the bearing capacity of the structure is overestimated. Therefore, structural calculation model which can accurately simulate the mechanical hehaviors of single layer latticed shells should be established, and the dynamic damage mechanisms of single layer latticed shells under strong earthquakes should be deep investigated. In this paper some studies are carried out with theoretical analysis and numerical simulation.(1) Differential equation is created based on the deformed figuration of the structural member, and displacement interpolation equations of spatial beam element are deduced to model the structural member without axial force. By Maclaurin series expansion, the uniform displacement interpolation equations considering the second order effect for both tension and compression beam-column element are deduced to model the structural member with axial force. The element tangent stiffness matrixes considering axial deformation, shear deformation, two-direction bending, torsional deformation and coupling effects of all the deformations metioned above are deduced and the second order elastic calculation method for single layer latticed shells are established.(2) Two buckling types of the member of single layer latticed shells are presented. The plastic hinge member model considering the second order effect are used to simulate the pre-buckling member, and the Marshall model is used to simulate the post-buckling member. The ISO buckling criterion for spatial circular tube is introduced, and the elastic-plastic member model considering the buckling effect is established. By this model, the repeated buckling-straightening processes of the member of single layer latticed shells under strong earthquake and the forming-disappearing processes of plastic hinges can be simulated.(3) The characteristics of the load-displacement curve and plastic deformation develop process of welded hollow spherical joint under loop loading are studied. Based on the regression statistic method, the mechanical calculation model for welded hollow spherical joint are established by which the repeated loading-unloading processes and the damage processes of the joint under strong earthquakes can be simulated.(4) Numerical calculation model of single layer latticed shells based on the elastic-plastic member model and mechanical welded hollow spherical joint model are established. Whether the structural bearing capacity can keep balance with the seismic action is defined to be the dynamic damage criterion of single layer latticed shells, and the time that the structural nonlinear dynamic equilibrium equations do not converge is defined to be the structural damage time. The number and distribution of buckling members, the number and the position of plastic hinges and the damaged joints when the structures damage are studied, and the dynamic damage mechanisms of single layer latticed shells of different types under earthquake are summarized consequently.