Does bracing requirement change with end conditions? 1

[weron4u]

I have a cantiliver beam loaded at the end. According to AISC Allowable Steel Design, (Lb < Lu). My question is, is the effective unbraced length of a cantilever beam double the actual unbraced length.

I would assume that its ability to twist is greater than if it was a pin-support of the same length subject to the same load.

 

[haynewp]

No, you can use the actual length for the unbraced length for a cantilever beam.
Cantilever columns are a different story.

 

[dbuzz]

In Australian practice (AS4100) the effective length of an unbraced cantilver is:
- the actual length, for load height position at the shear centre
- twice the actual length, for load height position at the top flange

This is to account for the &quot;de-stabilising&quot; effect a load positioned at the top flange, which will increase the twist and lateral deflection.

 

[haynewp]

The ASD 9th clearly states that you can use 1.0 x the length as the effective length. However, there is more to it than either 1.0 or 2.0 times the length. Stability Design Criteria for Metal Structures presents a table regarding this topic. There is also a discussion at

http://www.seaint.org/sealist1.asp

search the archive for &quot;cantilever beam&quot;.