Numerical Simulation Research On Fire Resistance Of Steel Portal Frames

Steel has the advantages of high strength and recyclability,and is a green building material with outstanding overall performance.Steel structure buildings have incomparable advantages due to their light weight,and good seismic performance.In recent years,steel portal frames have been widely used in China.However,the material properties of steel will deteriorate rapidly under fire,which leads to the poor fire resistance of steel structure buildings,and the damage and collapse of the overall structure are extremely prone to occur.The research on the distribution law of temperature field and failure process of steel portal frames under fire is helpful to carry out the fire resistance design of steel portal frames,and is very important to the safe application of steel portal frames.Firstly,this thesis combs and updates the component-based fire resistance calculation method in the current “Code for Fire Safety of Steel Structures in Buildings”,and realizes the coordination with the current relevant standards.Secondly,the thermal parameters of the steel under fire are determined,and a finite element example is given to verify the existing steel structure fire test results,which confirmes the feasibility of numerical simulation using sequential thermal-mechanical coupling method.Thirdly,based on the fire resistance calculation of the overall structure,a typical portal frame is selected.The thermal-mechanical coupling analysis is carried out on the most dangerous single-layer variable cross-section steel portal frame directly above the fire source.The thermal dynamic response characteristics of the structure under different fire scenarios are studied.The effects of different fire surface conditions,different fire temperature-time curves and different fire protection measures on the temperature field distribution and overall fire resistance of the structure are analyzed.Finally,the fire protection measures that meet the requirements of fire resistance limit are given.The results prove that:（1）The fire surface conditions,the selection of fire temperature-time curves and the constructions of fire protection measures all have a certain impact on the temperature variation law of node temperature and the distribution law of the temperature field.（2）Under the various working conditions analyzed in this thesis,the failure mode and failure characteristics of the structure will not be changed by changing the number of fire surfaces,changing fire temperature-time curves,and taking different fire protection measures.（3）Taking fire protection measures can effectively improve the fire resistance limit time of structures.However,when the thickness of fireproof coating or fireproof board increases to a certain extent,the promotion range of the fire resistance limit of structures per unit thickness of the material will gradually decrease.In conclusion,the main work of this thesis can provide references for numerical simulation of the thermal dynamic response characteristics of steel portal frames,and provide references for fire resistance design of steel portal frames.