Origin of the 2% Bracing Rule

[KootK]

Engineers often brace compression members with bracing elements capable of resisting 2% of the axial force in the compression member.

Does anyone know how this rule of thumb was derived? Is it based on an assumed amount of misalignment / load eccentricity perhaps?

Given how universally this rule of thumb seems to be applied, I would find if comforting to know how it was developed.

Any insight would be greatly appreciated.

Thanks,

Kootenay

 

[WillisV]

thread507-240591

 

[KootK]

Perfect. Thanks WillisV.

 

[GalileoG]

The question that never dies...

Clansman

If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.

 

[msquared48]

Is that like the song that never ends?

Mike McCann
MMC Engineering

 

[demayeng]

I was told that if you had a perfect beam (or column) made from a completely homogeneous material the lateral restraint required would be zero. Even though the Euler buckling mode exists and the beam is in an unstable state, there are no forces telling it which way to buckle.

Natural material variations and out-of-straightness in real beams generate small P-delta effects - the 2.5% (or 2% in the US) restrains against these.