AISC Table 3-10

[jreit]

Hello everyone.

I had a question about Table 3-10 of the AISC Steel Manual 14th edition.
I wanted to know what the dashed lines being cut off beyond a certain Lb represented.
For example, on 3-134, a W12x19 member does not extend beyond a Lb of ~10.25'.
Does this mean if I use a W12x19 with a Lb of 12', it will not behave according to the equations in Section F2 and it will not have a flexural capacity of 22 kip-ft (with Cb = 1.0)?

Thank you.

 

[WillisV]

Solid Line = W-shape for that curve is the lightest cross section for given combination of flexural strength and unbraced length
Dashed Curve = not the lightest cross section that could be used
Capacities are still correct.

 

[Archie264]

And, "...the plotted curves are arbitrarily terminated at a span to depth ratio of 30 in most cases."

 

[JAE]

The end of the line represents the maximum Lb that can be used with that beam - beyond that I believe it is simply unstable and should not be used.

The discussion for that table (prior to the table)in the manual suggests a cut off of span/depth = 30. However, the table isn't based on span but Lb so I'm not sure what they are talking about.

For your beam (W12x19) the limit appears to be 1/3 of a span/depth = 30.

 

[JAE]

Sorry - Archie beat me to it.

 

[jreit]

Thanks a lot everyone.