Lateral Torsional Buckling Of Cold-formed Thin-walled Hollow Flange I-section Steel Beam

Steel beams generally used as bending members in steel structures have mostly I-shaped cross-sections.When the upper flange is subjected to lateral loading or end bending moment loading.In the first,the beam will only bend in the main plane of maximum stiffness.After the load increases to a certain value(the component does not reach the yield strength in the main stiffness plane),Since the inertia moments of the two main axes of the I-shaped section are extremely different,the beam will simultaneously generate a lateral displacement outside its main stiffness plane and be accompanied by a corresponding torsional deformation.Finally,the beam will lose its bearing capacity at an extremely rapid rate.This is where the overall instability of the beam and also called lateral twist instability.At this time,the load that the beam bears is the critical load that causes the overall buckling.This situation is more likely to occur for moderate or large span beams without lateral support.for this beam The load carrying capacity and cross-sectional dimensions are often controlled by its overall stability.The overall instability of the beam is a kind of brittle destruction,which is difficult to detect beforehand,extremely hazardous in the event,and difficult to remedy afterwards.In order to improve the overall stability of steel beams,the cross-section of steel beams are improved in this paper.Two new cross-section steel beams are studied: the I-shaped rectangular hollow flange and the I-shaped triangular hollow flange.Through theoretical analysis and numerical simulation,the expression of the elastic critical bending moment of the new beam is deduced,Both ends of the beam are simply supported and the upper flange bears the lateral uniform load,And analyze the influencing factors,Obtained the following results(1)As the thickness of the slab increases,the aspect ratio increases,and the aspect ratio of the flange increases,the overall stability of an I-section steel beam with cold-formed thin-walled hollow flanges will increase,and its critical mid-span bending moment value Will improve.The effect of the aspect ratio on the overall stability is stronger than the aspect ratio of the flange.(2)With the same thickness,same section size and span,the overall stability of I-section steel beams with hollow flanges is significantly better than that of ordinary I-beams.The critical bending moment at the mid-span of I-section steel beam with rectangular hollow flange is approximately 4 times the critical bending moment value of ordinary I-beam.The critical bending moment at the mid-span of I-section steel beam with triangle hollow flange is approximately 4 times the critical bending moment value of ordinary I-beam(3)When the elastic lateral torsional buckling occurs in a cold-formed thin-walled triangular hollow flange I-beam,the critical expression of the mid-span critical bending moment is the same as that of a rectangular hollow flange I-beam.The difference between the two is that their parameters are different in value,that is,they are different in the principal axis moment of inertia,the warping moment of inertia,the moment of torsion,and the like.