Analysis Of The Limit State Of The Welded I-Section Steel Beams At High Temperature

The welded I-section is one of the cross section forms of steel beams.Compared with welded I-Section beam with biaxial symmetry,the monosymmetric I-Section beam has a good application value and economic benefit.It's more and more applied to practical engineering.In the design of the overall stability of the beam,the effect of the residual stress should be considered for it is one of the important factors that affect the overall stability of the beam.However,in the case of high temperature,domestic and foreign scholars believed that the residual stress would be completely released in the fire,and the effect of residual stress is abrogated in the stability of steel beam.Some considered the effect of residual stress but used the size and distribution of residual stress in normal temperature,so that the results were too conservative.In this subject,the strain release coefficients which affect the accuracy of the residual stress measured by blind hole method is simulated by finite element method,and the residual stress in the earlier test data were analyzed.At last,the stability of steel beam considered residual stress under high temperature environment is studied.In this paper,through applying theoretical analysis combined with the finite element analytical method,the strain release coefficients is simulated on the basis of earlier test data.And it is presented that when the ratio of hole depth and aperture is about 1.25,the value of the measurement is close to the calculation value of the hole.The influence of the thickness of board to strain release coefficients and calculated stress is very small and it can be ignored.Considered the size and distribution data of residual stress under high temperature environment is scarce,the residual stress of 12 monosymmetric welded I-shaped section(cutting edge)beams in 650? got from preliminary test data is simulated by finite element method,and the simulation results are compared with the results in 70?.The results show that:when the steel temperature is at 650?,the peak value of the residual stress in flanges is about 40%of the peak value at 70?,and the peak value of residual stress in middle web is about 20%at 70?.The distribution modes of residual stress in section are basically no change.At the same time,the calculation results are analyzed in group according to the specimens' depth thickness ratio of web,width thickness ratio of flange and flange width.Based on the finite element analysis of the residual stress under high temperature,the overall stability of the steel beam is analyzed by finite element method.By studying the influence of the size and distribution of residual stress and the depth thickness ratio of web to the specific node displacement in single span simply supported beam and two span continuous beam.It is shown that,(1)for the node displacement in the edge of midspan flange of' single span simply supported beam,the difference between the value with the effect of the residual stress at high temperature and the value with the effect of the residual stress at room temperature is more than 31%;for the node displacement in the edge of midspan flange of main span of two span continuous beam,the difference between the value with the effect of the residual stress at high temperature and the value with the efcct of the residual stress at room temperature is more than 22%.By comparison,the amplitude of the displacement of the single span simply supported steel beam is larger than that of the double span continuous beam,and the choice of the residual stress is more important for the single span simply supported steel beam.(2)With the increase of the web height and thickness ratio,the displacement of the nodes in the edge of midspan flange has a tendency to decrease,so it is appropriate to increase the height of the web in the design of the steel beam;With the increase of the flakiness ratio of the flange,the displacement of the nodes in the edge of midspan flange has a tendency to decrease,so it is appropriate to increase the flakiness ratio of the flange in the design of the steel beam...