Lateral buckling force 1

[pphawk]

Hi everyone. I'm trying to calculate the force magnitude of the lateral buckling of a slender steel girder. I know that my beam is going to buckle so I will use lateral support attached to a wall but I dont know how to calculate the strenght of this lateral supports because I need thid force. Thanks for your comments.

 

[CJJS]

2% of the axial load is the generally accepted rule for the lateral brace force.

 

[UcfSE]

You should follow the AISC's bracing strength and stiffness requirements. The specification is a free download from AISC.org and can be found here.

 

[blake989]

Also see AISC LRFD 3rd Edition...specification Chapter C, use relative bracing formula, not the nodal. the required force in the brace will pop out of the Pbr equation.

 

[RARWOOD]

UcfSE

I went to the AISC web site but didn't seem to find information on bracing and stiffness requirements. Could you provide a little more information on the title of the document.

I work with wood trusses and deal with questions about truss bracing a lot. The question comes up when bottom chord bracing is not provided.

 

[pphawk]

Because of space and money, I couldn't use a non compact section so I decided to use a slender section girder near to a concrete beam. the distance between both is almost 6 inches. I have to use lateral support in order to avoid lateral torsional buckling but I need to calculate the load applied to these supports. I will find out what is wrriten on the AISC-LRFD about this subject. Is there another way to find out this load?

 

[UcfSE]

On the site page from the link I provided, under Related Files, you find a link to the 2005 specification. Section C1.2 of the 2005 specification directs you to Appendix 6: Stability Bracing for Columns and Beams. That may or may not help you with requirements for wood.

 

[J1D]

UcfSE,
I'm not sure the meaning of the "brace stiffness" there. Fox example, I calculated BETAbr = 6 kip/in from Eq. (A-6-2) in the Appendix. Does this mean the 6k/in is the minimum EL/A value of the bracing member?

 

[J1D]

I mean EI/(AL), the unit is k/in as well.

 

[UcfSE]

I don't use the spec too often but that sounds like a reasonable conclusion. I believe you mean AE/L.

 

[RARWOOD]

UcfSE

Thank you for the additional information on the AISC web site. I down loaded Appendix 6,which will be helpful to me, in some applications.

 

[J1D]

You're right, UcfSE. EA/L is the axial stiffness of a prismetic member. Thanks