Research On Analysis Method For Limited Capacity And Damage Immunity Of Spatial Latticed Structures

The damage immunity of spatial latticed structures refers to their ability to adjust the internal forces to avoid the progressive collapse and maintain the whole structure stability, when local members or joints failed as a result of accidental events. Because abnormal events are elusive and difficult to quantify, the effect of abnormal events is not considered in current codes and standards. Only some simple clauses prescribe, "For abnormal load case, the progressive collapse should not occur when the structure is designed according to limit state of bearing capacity". So the engineer has no warrant to consider the abnormal event in design. And the current design method can’t give spatial latticed structures sufficient safety of unexpected accident. Because spatial latticed structures are widely used in large-scale public buildings presently, we should estimate the damage immunity of large-scale public buildings besides analyzing the strength, stiffness and stability due to their significance and higher safe class. The main research work in article concerns the status evaluation method of limited capacity and damage immunity, and the design method based on damage immunity is adopted to improve progressive collapse resistant capacity of spatial latticed structures. Thus the happening of progressive collapse accidents of spatial latticed structures can be avoided. The research work on measurement, estimation and alert to the spatial latticed structures in service is valuable and significant.In this paper, referencing the national and international research findings on limited capacity and resisting progressive collapse, combining the specific demand of spatial latticed structures, the main contents of this dissertation and described as follows:1. The bar element’s tangential stiffness matrixes are deduced, which is based on the finite element method. The geometrical nonlinearity and material nonlinearity are both considered in the non-linear element stiffness matrix. Based on the above analysis and studying equilibrium path tracking method and iterative strategy, the program of full-range nonlinear analysis for spatial latticed structures is developed. Some classic examples are given, and then accuracy and reliability of this program are demonstrated.2. Start from all kinds of influence factors of the structural limited capacity, the main factors influence on the limited capacity was categorized as instability spreading, instability modes, struts instability, joint stiffness and shape deviation, et al. The reasonable strut-and-tie model was used instability members to considerate the influence on structural limited capacity for stiffness weakening. The influence of initial geometric defects was also analyzed. Based on these, proposed procedure of determining limited capacity of spatial latticed structures was brought up, which is verified by some numerical examples.3. Based the finite element method analyzing and probability method, the new method to calculate initial displacement and stress of spatial latticed structures was brought up. Based on the above analysis, the program of finite element analysis is developed. Then, through calculating examples, property analysis of spatial latticed structures with random manufacturing deviation was given.4. So far, the existing formula derived from theory of probability and reliability is suited to structural element, barely involving with the whole structure. Computing the limited capacity of spatial latticed structures by reliability theory was attempted. The checking formula expressed with partial coefficients was suggested. Comparison of the results of numerical examples and test data on formula from related code shows that the checking method determining spatial latticed structures on reliability index is feasible.5. Measure method of damage immunity for spatial latticed structures is presented, and the program of damage immunity analysis is developed. Design method of damage immunity for spatial latticed structures is also presented, which includes structure calculation and construction design. The damage immunity was graded three levels according to the importance and functional requirement of buildings. For the lattice structures of level 1, damage immunity should be considered by structure calculation during the structure design. For the lattice structures of level 2 or 1, damage immunity should be considered by construction design during the structure design. For the lattice structures of level 3, damage immunity could not be considered during the design. And then the structure design procedure based on damage immunity was brought up.