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Unbraced Length
4

thread507-469169

Unbraced Length

Unbraced Length

(OP)
I have an Unbraced WF beam Pinned at both ends and a post at mid-span which places segments of both the top & bottom flanges under compression. Is it accurate to use the location of the infections points as the unbraced length (where the moment switches from + to -) or the total length of the whole beam?

Thank you

RE: Unbraced Length

It is inappropriate to use the inflection points as a brace point.

You would use the full span length but use a Cb factor (per AISC) on the moment capacity.
Or you could add a positive brace at the inflection point, or anywhere for that matter, to limit the Lb.

RE: Unbraced Length

Search "rafter without fly brace" in this forum smile

RE: Unbraced Length

Do not use inflection points as braces. I believe this is even written in most codes. Inflection points aren’t 100% accurate.

RE: Unbraced Length

Is the post above or below the beam? Is the post braced laterally? There might be more to evaluating the stability of this system than just a standard unbraced length check on the beam. All I know right now is you have a pin-pin (torsionally restrained at ends?) beam that is unbraced and is supporting a post - doesn't sound too stable to me.

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