| For its significant advantages in stress simplicity, assemblage and cost efficiency, the portal frame has been widely used for industrial and civil construction. However, the structure generally has capacious space and good permeability. With large amount of fuel, a developing rapid fire can easily cause the portal frame to damage or even collapse under the action of air convection. Therefore, the research on the mechanical properties of the structure under natural fire, and puting forward the scientific and reasonable design recommendations, has important theoretical and practical significance. At present, numerical simulation developed for modelling the behaviour of portal frames subject to fire mostly concentrate on static formulations, while the numerical analysis based on the fire tests and a three-dimensional analysis is insufficient. To counter the problems above, the specific content of this paper is as follows:(1) Based on the brief summary of the characteristics of large space fire, fire loads and fire scenario design method, the FDS (Fire Dynamics Simulator) was employed to simulate various scenarios of portal frames in order to obtain the temperature-time curve of the whole-process in fire.(2) A simple folded beam model was modelled using quasi-static analysis method by ABAQUS. In comparison with the results by static analysis and explicit dynamic analysis, it shows that the quasi-static analysis by introducing specify dissipated energy fraction can improve the convergence rate after an initial loss of stability partial failure of the portal frame. At the same time, it is able to capture the critical temperature and fire resistance time accurately.(3) The experimental model subjected to natural fire was established based on quasi-static analysis method using ABAQUS. Comparison with experimental results shows that the analysis on the basis of a single-span portal frame can’t capture the behavior of portal frame under fire but a three-dimensional model meets well with the experimental results, when the portal frame lose stability.(4) On the basis of analysis of experimental model, three typical portal frame models in Light-Weighted Steel Portal Frames were built using ABAQUS, which is to study the collapse mode of potal frames and the critical temperature. After a large number of numerical analysis, some parameters such as protection measures and column base restriction were investigated when the structure deforms in an outwards way. According to the results of the analysis, fire-resistant design recommendations are presented. |
