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Depth of Crane Beam Bracing 3

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JoshH726

Structural
Aug 3, 2010
83
Evaluating a 5T crane beam originally installed mid-1970s. Running through preliminary numbers, I'm discounting the bracing shown as any type of App. 6-level bracing. Unfortunately that eliminates all capacity in the system. App. 6 says bracing at or near the compression flange, but I don't see it being effective this far down. However, the question I'm going to get pushed back on if I say to reinforce it is that "we've been using this for years with no issue". My gut says the bracing must be doing "something", but I'm not sure how to quantify it. Any suggestions?
 
 http://files.engineering.com/getfile.aspx?folder=f6e51714-6617-4e7f-aeab-57b214c9ab15&file=20170515163228693.pdf
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Lomarandil, if you go to the amazon page linked by Ingenuity you can actually preview some of the pages relevant to load height on flexural buckling. Should give you a good idea of what the book has to offer.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
 
Interestingly, at today's AISC live webinar Link on the design of underhung cranes the subject of load-height was obviously discussed. The presenter, Lucas Pachal, presented the SSRC 4th Edition method and directly used calculations with the SSRC MODIFICATION, as follows:

Capture_ziourr.png


In the SSRC-4th Edition method, the "beam parameter", W, is identical to Trahair's "torsion parameter", K, so both methods yield the same result.

If you apply the SSRC MODIFICATION method, it assumes a constant load-height factor of 1.4, disregards the type of loading (distributed or concentrated) and simply modifies the bending co-efficient, Cb, so something like this:

Capture_ybgda5.png
 
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