huangyhg

slenderness ratio
is there a preferable range for slenderness ratio? i.e. is it preferable to have my slenderness ratio fall into a specific range like, say, 90-150? i have a column that checks out ok, but the slenderness ratio is at 190. my tendency would be to simply bump up a size (increase the radius of gyration). what do you guys think?
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i think there used to a limiting slenderness ratio of 200 for compression
i've attached my calc for this simple design. it is a simple pipe support inside a building, so there won't be any wind load. i didn't attach the base plate or sonotube calcs as they don't really pertain to my question. let me know if i'm doing anything wrong.
slickdeals,
i know that aisc recommends not exceeding 200, but my question is what if you're approaching it? if you see my attachment in the previous post, you will see that my slenderness ratio is 188. is it good practice to bump up my column size to lower the slenderness ratio? thanks in advance.
adam
this thing's going to be pretty wobbly (side-to-side), no ? (with only a cantilevered base) ... if somebody pushed on it at the top, say 50 lbf *17' = 850 ft.lbs ... i'd be looking to brace the support somehow rather than making it a slightly bigger section.
if your limit slenderness is 200, but you in practice avoid it (by designing to say 160), then your limit is 160, no?
rb1957,
actually the base connection will be pinned (base plate). i have it shown incorrectly on my load diagram... bracing is out of the question as the client wants as much open space as possible, in addition to it blocking key access ways.
i'm a little lost as to what you mean by the last line, in which you wrote, "if your limit slenderness is 200, but you in practice avoid it (by designing to say 160), then your limit is 160, no?"
how about extending it up to the roof ?
how about a lateral brace up at the pipe level ?
what's going to keep the top of the support directly above the base ?
how are you attaching the pole to the base ? clevis ? edge weld ? there'll be some moment stiffness there, just not much. as your calc show, the load is off-set from the pole's axis, so statically you need the moment reaction. how is the off-set accomodated in your column calcs ? (fa is pretty darned small, 4ksi)
you're supporting insulated pipes .. these'll impart no (ie zero) lateral load on the pole ?
but even if the calcs based on intended loads and geometry show it good, what unintended loads could produce an unintended geometry that isn't good ?
rb1957,
these supports are inside a compressor building within a large hydrogen plant. the client does not want any bracing of these supports. with that said, the piping itself will add some rigidity, but the pipe stress engineers tell me there is no side load. i cannot go to the roof as it is another 30 feet or so (doesn't make much sense to extend the column an additional 30'). client said no to lateral brace at piping elevation. the column will be welded to a base plate, with the plate having 4 cast-in-place chemical adhesive anchors (1" grout underneath the plate). i designed the base plate to account for the moment reaction. the only unintended loads i can think of is if someone runs into one of these supports with a forklift.
hey, you're the guy signing for it ... to me it looks pretty wobbly ...
just noticed your moent sum is way off (too high, by miles) ...
p1*17' ? should be p1*0.75'
same for others
what about weight ? (17'*7.6in2*0.3 = 465lbs
you can't design a frame with pinned bases and pinned beam connections. it's inherently unstable. whether the pipe engineer says there is a lateral load or not, there will be some lateral load (even is it only nominal), be it from being built out-of-plumb, someone bumping into it, etc. you can't completely neglect a lateral force.

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