K factors of Frame/Platform Legs
K factors of Frame/Platform Legs
(OP)
Anyone have any experience with choosing K-factors of platforms for un-braced and/or braced legs?
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K factors of Frame/Platform Legs
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K factors of Frame/Platform LegsK factors of Frame/Platform Legs(OP)
Anyone have any experience with choosing K-factors of platforms for un-braced and/or braced legs?
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RE: K factors of Frame/Platform Legs
RE: K factors of Frame/Platform Legs
Unless you have diagonal braces, you CANNOT just use K=1. That would be heinously unconservative for many cases.
DBD
RE: K factors of Frame/Platform Legs
RE: K factors of Frame/Platform Legs
RE: K factors of Frame/Platform Legs
-Mike
RE: K factors of Frame/Platform Legs
RE: K factors of Frame/Platform Legs
Also, K=2 is not a catch-all conservative effective length factor. If you have a fixed base, then K=2 is the upper limit. If you have a pinned base, then K will likely exceed 2. There's no substitute for actually calculating the correct value.
DBD
RE: K factors of Frame/Platform Legs
Theoretically a column fixed at the top and bottom with sidesway will have k=1.2 per case(c). If the base were properly shimmed, grouted, and bolted down then that would be the appropriate value. If the bolts would loosen up however, the pinned base assumption would be more accurate. And there are probably many onsite reasons why bolts may not stay tight.
-Mike
RE: K factors of Frame/Platform Legs
I would use k=2 as a starting point and then when you get some preliminary members I would go back and use the logarithmic charts given in the AISC manual to choose a more accurate k. Keep in mind there are a lot of assumptions built into those k charts so they aren't necessarily the "theoretically correct" tools we sometimes assume. The main thing is to provide for your assumptions. If you assume nonsway or braced frames for instance then the top of the column needs to have translation prevented to such a degree that your assumption is correct, and the same for the base fixity at the footing.
RE: K factors of Frame/Platform Legs
RE: K factors of Frame/Platform Legs
-Mike