Study On The Limit Temperature Of Steel Frame Structure Using Quasi-Newton Method

Because of light weight, high strength, high reliability and good aseismic performance of mechanical properties and building utility, steel is getting more and more widely in industrial and civil buildings。But steel is a kind of material which is more sensitive to temperature, once structural fires, steel strength will be reduced in a short time, deformation increase quickly, when the temperature is more than 550℃, steel will lose most of strength and rigidity。In order to make steel structure can keep persistent under the fire, we must calculation and analysis ability to resist fire of steel structure for the ultimate temperature of the collapsed structure, According to the extreme temperature, we must be ready for against fire of component or structure in order to make structure meet the design requirements of limit state for fire resistance。Currently, there has been some relevant design specifications of fire to the civil building, For the steel structure of the large petrochemical facilities, due to the steel structure to meet the hydrocarbon fire resistance requirements, both design specification and performance analysis are the lack of sophisticated methods, this paper carried out the corresponding research.in order to solve this problem。Steel frame structure is as a whole to withstand loads, The destruction of a small number of components does not mean a whole structural damage under the high temperature in the fire. Since the destruction of a small number of crossing a component will lead to redistribution of internal force of structure, therefore, the structure can still bear load, and will not immediately collapse。The study about the limit temperature when the structure collapsed is more realistic significance than the limit temperature of single component damage, For relatively simple structure model, we can use the superposition method of the basic failure mechanism to the extreme temperature。But for a relatively complex steel frame structure, If we still use the superposition method, enumeration method will make huge computation。Therefore, in order to to solve this contradiction, this paper proposed the use of quasi-newton method, established format of the corresponding numerical calculation, writed the corresponding computer program, And through six specific engineering examples of calculation results compared with the enumeration method to verify the correctness of this method, This method not only solves the limitations of commonly used analysis methods, but also the use of computer programmed to make calculations easier。The core of this method is transformed a very complex proplem of structure collapse due to fire load into solving extremal problems of multivariable function with quasi-newton method。...