Stability Analysis Of Elastic Steel Beam-columns Under High Temperature

Because of comparing with brick structure and reinforced concrete structure, the Steelstructures which are high strength, small weight, big ductility, good seismic performance,good construction progress, flexible layout, reused, environmental protection and soon,have prominent advantages，so they are widely used in the buildings. But the fatalweakness of the steel structure is fire-resistance. Under the fire, because the temperatureincreases, the material properties and the mechanical properties of the steel structure have ahuge change comparing with the properties in the normal temperature. Such as when thetemperature is300degrees centigrade，the yield strength and elastic modulus of steel began todecreased obviously；when the temperature is400degrees centigrade，the yield strength ofsteel will be halve, the elastic modulus down to about60%than before. After the temperatureis600degrees centigrade, the steel structures have a significantly plastic deformation and itsintensity and rigidity will nearly diminish. Due to the slender beam-columns have the functionof pressed and bended which often in the building of the frame structure,when the firehappened, they are more vulnerable to be damaged, so the people who live in this kind ofbuildings will suffer the great harm in lives and properties. For this reason, I analyzed theslender beam-columns which are in the high temperature in this text.First of all, the steel structures in high temperature are described about the presentsituation of researched at home and abroad in this text, and fire hazard and its developmentare also expounded in this text. This paper describes the physical properties and mechanicalproperties and their change rules of the steel in the fire about the present situation ofresearched of all countries, gives the protection measures of steel structures in the fire.Second, this text summarizes the heat transfer processes and the basic way of heattransfers in fires, and gives the calculation methods in fires of the air temperature rise andsteel structures’ temperature rise. With my hard working, I summarize the stability analysismethod of the slender beam-columns which their both sides are hinge joined and lateral loadseffect on them, in high temperature from the calculation methods of the slenderbeam-columns in normal temperature.Finally, for example, for the uniformly distributed loads and concentrated loads ofslender beam-columns, I analyzed the action of them which are a rounded by the protective layer in the fire and summarize the rules of the changing physical parameter rules. At thesame time, I use the deduction stability analysis methods of the slender beam-columns in thefire,to judgment the example construction members`stabilities. And using the results fromthat the ANSYS software analyses the two kinds of slender beam-columns, comparing withthe formula calculation Results, I get the corresponding conclusion.