Load position (load height)for LTB (AISC-360)

Yours_Sincerely · Aug 18, 2024

Hello everyone!
Could you help me to understand how to account for load height factor by AISC-360 when you calculate LTB? For example, if the lord is applied to the top flange then it is the worst case, if to the bottom flange the get restoring moment etc. I haven’t found any parameters considering this in AISC 360 or maybe I have just missed it.

Could you please help me where exactly in the code I can find any coefficients for it? Or are there are any other documents where it could be found?

lexpatrie · Aug 18, 2024

It's not in AISC, the more involved stuff is in the Stability Design Guide for Metal Structures (Ziemian ed, previously Ted Galambos).

The AISC code allows more sophisticated approaches to C[sub]b[/sub] (and other items) but I forget the language or where it is, precisely in the code.

C[sub]b[/sub] is only relevant for unbraced lengths beyond L[sub]p[/sub], and will not exceed the plastic strength of the section.

Smoulder · Aug 20, 2024

The commentary gives a method for top flange loading on I beams. Ignore part of the capacity formula so you get a lower capacity.

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Load position (load height)for LTB (AISC-360)

Yours_Sincerely

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