| Large space steel structures are extensively utilized in public buildings, industrial buildings and warehouses due to their enormous internal space, magnificent and beautiful architectural style. With the fast development of large space steel structures, the fire resistance capability and design method of these structures are attracting more and more attention. Large space building fire is different from the compartment fire, thus traditional fire resistance design approach under standard fire conditions is not suitable for large space steel structures. The performance-based design method as an alternative is appropriate for these buildings.In recent years, a few studies have been carried out to investigate the performance-based design method of large space steel structures. However, the research is still inadequate and the practical fire resistance design approach has not appeared yet. Therefore, based on the concept of performance-based design, experimental study, theoretical analysis and numerical simulation have been carried out to investigate the temperature field and the mechanical response of whole structures under natural fire. At the same time, the temperature development calculation model of steel members and fire design method of large space steel structures were studied meticulously in this dissertation. The main research contains and the main achievements are as follows:(1) By reviewing the relevant literatures and comparing the research results of different researchers, the methods for determining the fire load density and the heat release rate of a fire source were systematically summed up. The criteria related to fire spreading and flashover were presented. A simple procedure was proposed to assess the minimum size of the opening that can supply enough air to sustain the combustion.(2) According to the direct analysis method for steel structures at the ambient temperature and the relevant works, a modified research process has been developed to predict the fire performance of large space steel structures under natural fire. The distinctive aspect of the direct analysis method is that it can be used to predict the global behavior of structures subjected to fire without assuming the effective length. So the analysis approach provided in this dissertation is reliable and effective than the existing method.(3) A portal frame structure with a scale reduction of 1:4 was designed and built for natural fire tests. The structure was a single compartment which covered an area of 6 by 12.5 m. The columns were 2.25 meters’ high and the roof was inclined at 1/10. A diesel pool fire was used as a fire source. Five localized fire tests were conducted in and out this structure. The main purpose was to investigate the fire development and smoke movement, the centerline plume temperature, the temperature development within the whole building and steel members, the radiation heat transfer of flames, and the corresponding structural responses. The results indicate that the integral structure keeps safe due to the mutual effect of the whole system.The FDS was then adopted to simulate the fire scenarios occurred in the building. Besides, advanced 2D and 3D models were built in the ANSYS software to predict the behavior of the test structure in fire. The comparison of numerical results with actual fire test observations is satisfying, which gave increased confidence in using FDS and ANSYS to conduct numerical studies.(4) The various axisymmetric plume models were discussed and amended in this dissertation. Then a simple formula was recommended for determining the plume centerline temperature in a localized fire on the base of experimental researches. The formula can be used to conduct a preliminary evaluation of the structural behavior in fires. So the complex fire simulation and global structure analysis are not needed when the structure keeps safe during the fire.(5) Based on the results of theoretical analyses and experimental studies, calculation models for tracing the temperature development in steel members exposed to a nature fire in large space buildings were proposed for EC3 and 《Technical code for fire safety of steel structure in buildings》 (CECS200). Different formulas and parameters were adopted in the flame zone and the hot smoke zone, the zone under the hot smoke layer. The predictive temperature-time curves from the calculation model agreed well with the test results.(6) By considering the effect of smoke ventilation and fire spreading, fire scenarios occurred in a portal frame factory and a shopping center were simulated with FDS. The fire performance of the portal frame structure and the single-layer latticed cylindrical shell, which is the roof structure of the shopping center, was studied using the direct analysis method. The tendency of the temperature development for the hot gas in the building and steel members was discussed, together with the deformation characteristics and mechanical behavior of the structural system. And some advices were given in the fire-resistant design of related structures. On the base of above research works, this dissertation put forward an improved performance-based fire resistance design method for the large space steel structure. |
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