| The fire resistant capability of steel is very weak，because the strength of steelwill decreases rapidly to1/3of the normal temperature strength when the temperaturereaches600℃. So that a local fire can easily cause steel structures to damage or evencollapse, and the collapse mechanism of steel structures under fire is a hot topic infield of fire resistance of structure.Based on relevant results and the completed fire tests on steel structures, the fireresistance, initial collapse mechanism and simplified analysis of whole structure underfire are studied in this paper. Firstly, the initial collapse failure mechanism of steelstructures under fire are analyzed with nonlinear static analysis method, and collapsemechanism of steel structures induced by the interior heated column is analyzedaccording to the test results. Secondly, a static-dynamic conversion method isdeveloped for progressive collapse analysis of steel structures, and the failuremechanism is analyzed with the nonlinear dynamic analysis method. Finally,according to the initial collapse mechanism, an energy-based simplified analysismethod and structural fire response spectrum are proposed. This will provide a newanalysis method and reference for design and evaluation of collapse performance ofhigh-rise steel structure under fire. The main contents are followed:(1) Numerical analysis has been carried out based on the experimental results ofsteel frame structures under local fire, and the collapse mechanism of steel structuresinduced by the interior heated column is analyzed. Column buckling temperature,column failure temperature, and structural failure temperature are defined based onthe simplified collapse evaluation method.(2) A static-dynamic conversion analysis method has been developed based on thepredefined field and restart function of ABAQUS. Applying this static-dynamicanalysis method, the failure process of a steel structure under local fire has beensimulated and the initial damage mechanism of multiple steel structures caused by thedamage of column has been studied. The influence of restraint stiffness and load levelto the initial damage mechanism of steel structures under fire conditions and dynamiceffect of the whole structure has also been analyzed.(3) A simplified collapse analysis model with single degree of freedom isestablished based on the initial collapse mechanism of steel structures under fire, andthe energy-based formula to calculate the structure response is deduced. Therationality and feasibility of the proposed model and method are validated bycomparing with the numerical analysis results.(4) In order to further simplify the design method of structure under fire, theconcept of structural fire response curve are proposed based on the structural fireresponses, and the corresponding response curve for specific structures is established.. |
