Research And Application Of Mechanical Properties Of Steel Structure In Fire Conditions

The steel structure has excellent strength and extension attributions,and also has the advantages of light self-weight, short construction cycle, being easily industrialized and commercialized over other structure forms, so it is widely used in workshops, huge public facilities and high-rise buildings in China. However, its poor performance under high-temperature conditions is an inevitable fault of steel structure preventing its more widely application in engineering practice. For example, yield strength of steel will halve at the temperature of 400℃, and its intensity and rigidity will nearly diminish at 600℃. Research on fire-resistance characteristics of steel structure can not only reduce or avoid the possibility of structure destroy under fire, but also provide scientific basis on how to save material and raise stability coefficient of steel structure in its fire-resistance design.Taking steel Q235 as the test object, the change of mechanical attribution indexes such as yield strength, ultimate strength, elasticity module and extension rate under high temperatures and stress-stain relationship curves are summarized from experimental data, and are compared with the related research results obtained by some domestic and foreign researchers. Thus the selection method of some parameters of steel Q235 in its fire-resistance design is suggested.Subsequently, basic steps of steel structure fire-resistance design are described in the thesis. Having compared the domestic and foreign steel structure design regulations under fire, we discuss main measures on steel structure fire-resistance. On the basis of the research achievements of domestic and foreign steel structure design under fire, the calculation principle of steel structure fire-resistance in the ultimate bearing capacity conditions is presented, the computing methods of fire-resistance time, temperature increment and temperature inner fore are suggested, several required emphatic problems in its fire-resistance design are listed as well.Experimental and theoretic research results developed in the thesis are applied to the fire-resistance design of steel structure project of Dongfeng-Nissan motorcar 4S shop on XiangFu Road in Changsha. This design wins good feedback from the owners.