Column/Beam buckling

[cookyb]

Does anyone have good info or know where I can find info on the bracing force required to resist column and beam buckling? I need this for both steel and wood.

Thanks

 

[MotorCity]

A common rule of thumb is to use 2 percent of the buckling load for bracing against buckling.

 

[cookyb]

Thanks MotorCity.

By buckling load do you mean the axial load applied to the column? Also, for a beam are you calling the buckling load the distributed load tributary to the brace?

Do you know of anything in writing I can use to back up my own calcs?

Thanks again.

 

[MotorCity]

Use 2 percent of the Euler buckling capacity, not the actual load. I've heard rumors of this rule being published but I have never come across it.

 

[WillisV]

cookym - AISC provides guidelines for bracing considerations in Appendix 6 of the 13th edition manual (Chapter 3 of the 3rd Edition LRFD manual). The 2% rule MotorCity uses is outdated and though typically adequate for strength considerations, most braces will be controlled not by strength but by the stiffness required to act as a brace as spelled out in the aforementioned AISC provisions.

 

[Denial]

The rule about X% was in several Australian design codes back when I began working, thirty-odd (very odd) years ago. However I think the rule was 2.5%, and was expressed as "one-fortieth". If it was in the Australian codes it would also have been in some others.

The rule disappeared a while ago, presumably as a regognition that the stiffness of the bracing was as important as its strength.

 

[SlideRuleEra]

For wood, see the American Wood Council free .pdf download "Designing for Lateral-Torsional Stability in Wood Members" at this link

http://www.awc.org/pdf/tr14.pdf#search="lateral torsional buckling tech report 14"

http://www.SlideRuleEra.net

 

[JAE]

AISC now has a section in its specification that deals with this....under the newest (13th Edition) AISC Manual its in Appendix 6. Under the Third Edition LRFD - Section C3.

 

[cookyb]

Thanks everyone.

Unfortunately we don't have the AISC 13th edition in our office yet. But what I am looking for is not so much the critical buckling load (Euler), but what force is required to keep the column from buckling. I currently have a column that is 20' tall and is unbraced, and the axial load is higher than the critical buckling force. So if I brace this at the center of the column I can lower my effective length and be able to support more load on my column. But what force/stiffness needs to be present at the bracing point to keep the column from buckling? I would imagine that the bracing force needs to increase with the axial load being applied, but I don't know how to relate the two. Any thoughts on this?

Thanks again!

 

[JAE]

Even though you don't have the AISC manual, I'd suggest you get it as the sections I indicated provide both the required strength and the required stiffness of the braces required to prohibit buckling.

 

[UcfSE]

The new 2005 steel specification is a free download at AISC.org. You can get the specs, just not the whole manual.

 

[JAE]

Yes,....good point UcfSE!

 

[cookyb]

Thanks!