Research And Application On Mechanical Behavior And Evulation Method Of Post-fire Spatial Structure

Spatial steel structure has been widely used in China by its virtue of magnificent shape, attractive appearance and enormous interior space, etc. Steel is the primary building material in support system of spatial steel structure, with the advantages of transport efficiency, convenient construction and industrial-ized, etc. However, weak fire resistance of steel material performance can make spatial structure easy to damage or even collapse subjected to fire.The research on structural fire design is still at starting stage, it is not clear about response mech-anism and mechanical properties of steel strcuture subject to fire, the recover of structural temperature fields lack a certain foundation. Therefore, it is vital important in theory and engineering practice to further understand fire-resistance performance and the reverse problem of presumption of structure tem-perature fields. Theoretical analysis, numerical simulation and fire test have carried out hereby to inves-tigate the mechanical performance of spatial structure subject to fire, on the basis of forward analysis, further investigating the inverse method of structural temperature fields and constructing an inversion optimization algorithm. Space truss structure as illustrator, the main research work covered in this paper includes:In combination with calculation method of spatial structure in room temperature, expanding the ap-plicable scope of equivalent sandwich plate method. Numerical simulating the displacement response of space truss structure in period of temperature rising and the whole process of fire separately, through the study of statistical analysis on numerical results of displacements, a correction formula for displacement calculating of spatial structure in evaluated and post fire based on equivalent sandwich plate method, it simplifies the displacement calculation of spatial structure in fire.Base on the geometric characteristics of space truss structure, a temperature distribution model is proposed which is along the structural height direction. Structural stability discriminant conditions are derived, the geometric and material nonlinear properties are extensively considered, though different structural parameters analysing on the influences of structural stability, the change rule of space truss structure in evaluated temperature is obtained.An inversion presumption method is developed which named Inverse Method for temperature fields (IMTF). Assuming an initial temperature field based on the post-fire structure residual deformations, making the difference between measured and FEM values, and then constructing an inverse algorithm by selecting an eligible weight function to determine the final temperature field. Providing a theoretical basis for scientific evaluating the residual performances of post-fire structure and formulating reliable repair and reinforcement schemes.Fire experiments of Williams toggle frames and space truss structure are processed, the relationship of displacement and temperature are obtained. Appling IMTF on the structure of fire experiments, the collected test data are simular with the inverse presumption results by comparing. It verifies the method is feasible and the results have enough accuracy.The component importance coefficient of space truss structure subject to fire is researched, and the formulas of component sensitivity and structural redundancy are derived. An indicator of structure robustness is presented, which provides a new method for structural damage evaluation of post-fire space truss structure.Applying IMTF method in the post-fire TVCC structure which experimented a fire accident, a finite element model of zone F is established, which is spatial structure. Making the minimum value between measured and numerical solution of displacement points as the optimization goal, to obtain the tem-perature fields distribution that the structure experimented. Finally, make the temperature as the input parameters to solve the FEM structure, to verify the numerical precision of the method in the engineering application.