Collapse Mechanism And Collapse Resistant Measurements Of Single-Layer Reticulated Shells Under Strong Earthquakes

Single-layer reticulated shell is one of the main forms of space structures. The collapse of structures will result in serious deaths and economic loss. If some factors, like Bauschinger effect of materials, the member failure and fracture, are ignored in research on collapse mechanism of single-layer reticulated shells, the ultimate bearing capacity will be overestimated. Therefore, it is of significant theorial and practical value to study the collapse mechanism and collapse-resistance measurements of single-layer reticulated shells under strong earthquakes, considering Bauschinger effect of materials, the member failure and the member fracture.In this paper, the material constitutive model, the simulation method of member failure and fracture and the collapse mechanism of single-layer reticulated shell have been analyzed. This study contains the following work:(1) A novel elastic-plastic constitutive of circular steel tube is derived from the combined hardening, the cumulative damage, and Bauschinger effect of materials under cyclic loading. Based on the explicit method, a program is compiled to apply the elastic-plastic constitutive to beam elements. The performance characteristics of the circular steel tube are compared to measured results in the field to certify the correctness of theoretical analysis. The comparison shows that the program is accurate at evaluating mechanical behaviors of structures and members. The discrimination criterion of member buckling and the mechanical model of member post-buckling are all employed in the program. The tension and compression performance characteristics of simply supported beam are compared to measured results in the field to certify the correctness of theoretical analysis. The analysis results about a reticulated shell show that ultimate bearing capacity of structure is little affected by cumulative damage, but significantly affected by member buckling.(2) Based on discrimination criterion for component failure defined by the cumulative damage and the central difference method, the member failure is simulated by modifying member characteristics. Dynamic nonlinearity analysis is applied to the cantilever beam, and the node displacements from different simulation methods are compared to certify the correctness of simulation method for member failure. Considering cumulative damage and member buckling, progressive collapse of the single-layer cylindrical reticulated shell under earthquake is analyzed. The analysis results show that the simulation method for member failure can be used in the analysis of progressive collapse of space grid structures. Based on the simulation method for member failure, fiber beams are adopted to simulate member fracture. Comparing the simulations of different length members in fracture process, the reasonable number of fibers in section and elements along the member length is proposed. The member fracture in collapse process of single-layer reticulated shell is analyzed. The results show that, based on modifying member characteristics, fiber beam could be applied in the analysis of cumulative damage and fracture in member section and the collapse process of space grid structures.(3) The relationship of energy equilibrium is derived from dynamic equilibrium equation of structure under earthquake. Based on discrimination criterion for structure collapse defined by energy equilibrium, collapse mechanism of different types of single-Layer reticulated shells under strong earthquakes are analyzed, considering Bauschinger effect, the cumulative damage, member buckling and post-buckling, member failure and fracture. Collapse mechanisms of different types of single-Layer reticulated shells under strong earthquakes are summarized.(4) Partial double-layer reticulated shell is adopted to improve the collapse-resistance capacity. The natural vibration characteristics, the ultimate bearing capacity and the placement of buckling member in partial double-layer reticulated shell are analyzed. The results show that the ultimate bearing capacity of reticulated shell is increased by adopting partial double-layer, with dispersed position of buckling member and local failure of structures. Formula of energy dissipation of viscous damper under earthquake is derived from the central difference method. Energy proportional coefficient and displacement proportional coefficient are proposed to predict the optimize location of dampers in structures. The displacement reduction factors of single-layer spherical reticulated shell and single-layer reticulated cylindrical shell under earthquake are analyzed to certify the correctness of the optimization criterion.