Analysis Of The Steel Frame Structure Of Progressive Collapse Performance In The Case Of Fire Failure Of Column

Steel structure is widely used in building systems due to its advantages such as high strength,light weight and good toughness,but poor fire resistance is a fatal disadvantage.In the event of fire,the steel structure may occur serious local damage and cause progressive collapse.A brief review of the research process of progressive collapse,foreign scholars have been studying this for fifty years since the terrorist attacks collapsedin New York World Trade Center in September 11,2001.However,the research on progressive collapse started late in China.In the analysis of resisting progressive collapse of structures currently,a method the dismantled component which only pays attention to failure local member is used to assume member failure in general,but it can not be applied to the actual accident.In this paper,it was considered the whole collapse process of steel frame structure and evaluated the effect of each member accuratelyin the whole collapse process under the fire.The results lay a foundation for putting forward a method to resist progressive collapse mechanism and prevent the structure progressive collapse under accidental load effectively.The main contents and conclusions of this paper were shown as following aspects:1)Based on the finite element software ANSYS and collapse conditions of multi-storey steel frames in the existing literature,three different working conditions in the middle and corner regions were selected.A model of five stories and seven span steel frames under the fire model,external force and temperature load was established,at the same time,the nonlinear problem of physical properties and mechanical properties of materials was considered.The distribution of temperature field at any time was obtained,and then the calculation results of the stress field were obtained by using the indirect coupling method.Finally,the fire resistance and failure time of the fire member were obtained.2)Based on the method ofunit oflife-and-death,when the failed component of fire-affected component was demolished.The whole structure was analyzed by mechanics to simulate the deformation of the whole structure after the failure of components.Through the comparison of different working conditions,the damage mechanism and the collapsing danger of the whole structure under different failure conditions were obtained.3)In contrast to the existing literature directly lead to dismantling steel frame structure progressive collapse of[1]and considering the failure of fire numerical simulation results under the column,the column directly removed and did not consider the failure cause analysis of steel frame progressive collapse when the results were too conservative.The number of allowable failure columns for steel frames was determined in this paper.And through the calculation and analysis of the progressive collapse behavior of the remaining structure after the destruction of the local bottom column,the progressive collapse mode of the five story seven span steel frame structure was obtained.Based on research resultsabove,it was shown that the thermal structural coupling function of ANSYS was used to simulate the fire situation,combined with the life death element method to remove failure components,it can well simulate the progressive collapse process of steel frame under fire.It depended on whether the internal force redistribution can reach a new equilibrium state by analyzing the continuous collapse of each working condition structure.Compared with the existing literature[1]and results of this paper,it was found that the fire caused the failure of the column was close to the collapse of the real structure.For the analysis of the critical and collapse conditions,the collapse time and order of various working conditions were obtained,so that the collapse process of the structure was more specific and visualized than before.Finally,the condition of the middle part of the steel frame structure was obtained based on the selected working conditions,the number of failure columns allowed was less than three;For corner regions,the number of failed columns was one.It can be seen from the number of failed columns in the central and corner regions that progressive collapse was more likely to occur around the floors than in the center.