Investigation On Static Stability And Seismic Performance Of Keiwwit-Sunflower Single Layer Spherical Reticulated Shells

The investigation on the performances of the single layer reticulated shell, which is adopted widely as spatial structures, is one of the most critical issues in the field of study of spatial structures. Thought the Kiewitt-Sunflower single layer reticulated shells have been applied widely in the engineering practice, the performances of this structure have not been researched completely resulting in the fact that practice is divorced from theory. Therefore, the static stability and seismic performance of this structure are investigated systematically in this paper. The main works in this paper are submitted as follows:(1) Based on the theory of probability and mathematical statistics and on the results of nearly 7900 cases of elasto-plastic stability analysis for single-layer reticulated shells, the introduced method of the initial geometric imperfection in the static stability analysis of such structure is investigated. A new simulation method of the initial geometric imperfection distribution, N-order eigenmode imperfection method, with less calculation and high confidence is developed. The rationality of the proposed method is validated by the random imperfection mode method. Moreover, considering the internal force state of the structure, the influence extent of initial geometric imperfection on the structure and the realistic situation of construction, the reasonable maximum value of initial geometric imperfection is discussed, and the suggestion value is 1/500 of structural span.(2) The static stability of the Keiwwit-Sunflower type single layer reticulated shell is investigated through the large scale parameter analysis. Based on more than 15000 cases of elasto-plastic stability analysis, the buckling modes and failure modes of this structure are concluded, and the influences of the rise-span ratio, cycle ratio of Kiewitt cycles to Sunflower cycles, cross-section of members, load distribution, support condition as well as distribution and maximum value of the initial geometric imperfection on the static stability are revealed. Furthermore, according to linear regression method, the practical formulation of stability ultimate capacity of this shell is developed, which is provided for the engineering application.(3) The spatial hysteretic experiment is conducted for sixteen thin-walled steel circular tubes. The failure process and modes are concluded, and the variation of load bearing capacity, ductility, stiffness degradation and energy dissipation capacity during the loading history are examined. Also, the influences of the loading condition, axial load ratio, slenderness and steel strength on the hysteretic characteristics of specimens are evaluated. In addition, according to the phenomenon of the spatial experiment, a new damage evolution law suitable for steel components is introduced in the Lemaitre’s damage constitutive model, and then a new damage constitutive model for thin-walled steel circular tubes is developed within the thermodynamic framework. On the basis of experimental results, the parameters of the proposed model are determined by the inverse optimization method and the least squares fitting method. Finally, with the comparison of the numerical and test results, the availability of the proposed model is validated.(4) Based on the damage constitutive model proposed for thin-walled circular steel tubes, the seismic performance of the Kiewitt-Sunflower type single layer reticulated shell is investigated with the time-history method. The failure modes are revealed. The influences of the damage accumulation, rise-span ratio, distribution and maximum value of the initial geometric imperfection, seismic wave and adjustment ratio of seismic strength on the dynamic ultimate load are examined. Finally, the structural damage model for single layer reticulated shell under strong earthquake is proposed on the basis of displacement and damage.