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CFS: Discussion of Available Info on Design of Built-Up Box Beams/Headers

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Bill,

I used to design a lot of these, and I never used, and have never seen used the composite action of the top and bottom tracks. Think of a wood stud wall, have you ever tried to consider the double top plate in composite action with the header? The top and bottom tracks provide alignment & bracing for the Cees, and help to deal with the lateral loads.

I agree with Raymond's suggested design method of using the manufacturer's design properties for the Cees and the listed screw capacities for the connections.

There are also 2 very good software programs I am familiar with. 1) LGBEAMER, simple beam/column analysis with single members, built-up sections, and custom shapes. 2) CFS, the free version gives design section properties (including effective section), and the pay version includes beam/column analysis. I would recommend the software if you have very many designs to do, as the calculations can get very tedious by hand, especially combined bending/web crippling failure modes.

Hope this helps.

Dmitri Wright PE


From: Bill Polhemus <bill(--nospam--at)polhemus.cc>
To:  seaint(--nospam--at)seaint.org
Subject: CFS: Discussion of Available Info on Design of Built-Up Box Beams/Headers

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Greetings, All:

I am looking at a built-up box beam/header made from two C-shapes facing
lip-to-lip, nested inside a track shape on top and bottom. The C-shapes
face lip to lip but stand off from each other to rest against the
flanges of the tracks.

I'm attaching a JPEG of the shape for clarity's sake (size is only 6k).

Looking through the book "Cold Formed Steel Design" by Dr. Wei-Wen
Yu--assumed to be the Bible of CFS design--I really don't see much about
design aspects for this type of shape. I am assuming that one needs to
design fasteners (in this case, screws) to handle shears, etc., but how
does one approach the various checks one has to do?

Thanks for any illumination.




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