Effective Length Of Leg Angles With Alternate Supports In Transmission Towers

Angle is widely used in design of the various structures,such as roof truss,rain cover, .transmission tower,and so on.But due to the monosymmetrical of the angle section,it always need to consider the effect of torsion to the buckling load in the design of compressive members,because of this,the criterion use the method of conversion the slenderness ratio. But to the braced angle members,the effective length cannot simply take as the geometrical length[4],so this method cannot be used in the design of the braced angles directly.To this kind of the structure,Code for design of steel structure.(GB50017-2003) did not give the specific calculate method or the effective length factor,only in the.Code for design of tall-slender structures.(GBJ135—90) or the various reckoners,we can find the request of the effective length factor,and to the.transmission tower,that with alternate supports,the effective length factor is 1.2,and the radius of gyration take along the parallel axes.But there is not any explanation to the value of 1.2.In literature[15],without considering the effect of torsion,there gives some buckling loads of angel members in different spans with alternate supports,and we can find that the effective length factor of them is about 1.2.So we can know that the value 1.2 in the code is calculated only consider the bend by ignoring the effect of torsion.However,In literature[9],by considering the effect of torsion to the buckling load,there gives the effective length factor of the angle in K shape structure.And it indicates that the effect of torsion to the buckling load is huge,and it will change as well as the slenderness ratio and flakiness ratio,so cannot simply use a constant value to design or take the geometrical length as the effective length factor to calculate.Therefore,to the.transmission tower,with alternate supports,because of the support,it cannot ignore the effect of torsion.This paper used the energy method to analyze the flexural-torsional bucking load of leg angles in.transmission tower,with alternate supports,include the infinite spans,three spans and four spans,ultimately,we get the effective length factor of the leg angle calculated along the parallel axes.This paper gives the.effective length factor.with full.torsional restraints.and without.torsional restraints.on the supports.and compared them with the results that calculated by ANSYS.The effect of finite.torsional restraints,and finite bending.restraints.at the supports.to the.effective length factor,is also analyzed.And then a case of real .transmission tower.is calculated to analyze the effect of torsional restraints and bending .restraints.which provided by the supports.Finally,a new formula to calculate the.effective lengthfactor.is proposed.