Analysis Of Continuous Collapse Performance Of Steel Frame Structures Under Local Fire

With the development of society,the number of steel structure buildings is increasing,but poor fire resistance is a fatal shortcoming of steel structures.Once a fire structure is damaged,vertical structural damage will cause continuous collapse of the structure,and the consequences are unpredictable.It has important engineering value to study the continuous collapse resistance of steel structures,but China started later than abroad.This paper considers the overall response analysis of steel frame structures under the condition of failure of vertical load-bearing members due to high temperature of fire.Analyze the force transmission mechanism of the structure when the component fails,and accurately play the role of load distribution members around the failed component,so as to lay the foundation for proposing design methods to improve the structural collapse resistance and structural measures to reduce its probability of occurrence.The main research contents of this article are divided into the following aspects:(1)Using ANSYS finite element software to establish a steel frame model.Considering material nonlinearity and geometrical nonlinearity,a column of center columns fails to heat up under a standard temperature rise curve,and the temperature field at each moment of the structure is obtained.Axial displacement of components,fire resistance limit temperature.(2)The life and death element method is used to dismantle the fired column at the moment of component failure,and then the stress distribution of the eleven working conditions of the steel frame in this paper is obtained.The most dangerous positions are obtained and the design method is proposed.The resulting force transfer mechanism and the failure mechanism of the overall structure.(3)The continuous collapse analysis of pure steel frames with different longitudinal spans,layers,and heights in a row of columns under fire failure,and the failure time and limit temperature of fired members under different conditions were obtained;used for load-distribution columns It is related to the stress,deflection,lateral displacement of the beam and the failure mode of the steel frame structure at various moments,and summarizes the influence of different parameters on the continuous collapse performance of the steel frame.The main conclusions are as follows:(1)When a fired column fails,the beam generates a catenary mechanism to transmit most of its bearing capacity to the adjacent participating load distribution center column;when the fired edge column fails,its bearing force will be mainly distributed to Adjacent side pillars and middle pillars.(2)Stress redistribution mainly occurs in adjacent spans,and the number of spans continues to increase,which cannot increase the redundancy of the structure and thus improve the continuous collapse resistance of the structure.(3)The floor frame load applied to the steel frame at room temperature causes the initial stress on the structure.The stress in descending order is center column>transverse side column>longitudinal side column>corner column;beam column node>beam beam node>beam span.After the temperature load is applied,the stress on the column top and the column foot around the fired column first increases into plasticity,indicating that it is a weak position under high temperature and needs fire prevention measures.(4)The higher the number of layers,the shorter the fire column failure time,the greater the stress on steel beams and steel columns used for load distribution,the greater the deformation,the greater the danger under fire,and the lower the collapse resistance of the structure,so the frame should be increased in the design The cross sectional area of the column reduces the deformation at the frame column-steel beam joint.(5)When the floor height is less than 4m,for each additional lm of floor height,the maximum displacement of the fired column and side column will increase by 39.1%and 46.7%,respectively.The maximum stress of columns and side pillars was reduced by 3.4%,indicating that increasing the layer height improves the resistance to continuous collapse of the structure.When the floor height is greater than 4m,the maximum stress of the load-distributing beam changes little,and the maximum axial displacement of the failed column increases due to the increase of the slenderness ratio,and the lateral displacement of the steel frame and the deflection of the longitudinal beam span increase.Large,indicating that the continuous increase in layer height at this time has an adverse effect on the structure’s resistance to continuous collapse.