Another Tricky Question
Another Tricky Question
(OP)
OK all you structural analysis & design experts....I have the joy of analyzing & designing a stage / canopy that looks like a fine piece of oragami (see attached)
Any suggestions on how to approach this one?
Any suggestions on how to approach this one?






RE: Another Tricky Question
RE: Another Tricky Question
RE: Another Tricky Question
See if that helps.
Then again, an invisible orgami canopy is certainly lightweight, but you might have to worry about how to hold it down. 8<)
RE: Another Tricky Question
I need to analyze and do a preliminary design of this canopy / stage. The architect wants to use precast panels for the upper structure, and there will be a cast-in-place concrete slab on the base.
Funny, but when the architect built the model, they put a wire across the top to hold the one corner up (b/c it was tending to fall down), but we can't have any supports in the real structure, it is cantilevering out to the far corner.
I'll post one more picture after this one.
RE: Another Tricky Question
PS - the architect want panels & slabs to be as thin as possible.
We could put a rib on the outside edge if req'd and the end of the "box" can be solid, so I'm thinking a cantilevered triangular rib (along the outside edge), cast monolithically with a solid column / wall & a moment resisting base at the far end....
RE: Another Tricky Question
Indoor (stage only?) or exposed to real world wind and rain/snow/ice loads?
How tall to the points?
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My last attachment was a scanned pdf of photos, with mark-ups that explained all that, but I am having a "trouble with technology" day.
RE: Another Tricky Question
RE: Another Tricky Question
BA
RE: Another Tricky Question
Mike McCann
MMC Engineering
RE: Another Tricky Question
I am most concerned with overall stability & possible wind vibrations of the corner @ 11, but using concrete it should be fairly heavy compared to light steel framing.
PS - For the analysis, I know somebody a lot smarter than me can model this with thousands of nodes in SAP, etc. but I am wL2/8, moment distribution / hand calculations kind of guy - if this problem was in the 1960's, how would you handle it with some relatively simple but accurate enough calcs?
PS - I was in diapers in 1975....
RE: Another Tricky Question
Will it be erected as one piece? If not the joint will have to restore the continuity.
This one can be analyzed as a rectangular (square) plate with two free and two supported sides. It will likely be a plate of constant thickness, as I you can't have clamped sides. Determining the thickness under wind action and checking the frequency (higher than 5 Hz) will take you to a first check of feasibility.
I would also prevent the architect that, if necessary, some angles and inclinations could require changes: the angle between the panels joining at the line 2-11 is unclear in the photos, but seems quite small for transferring the load from panel 2-3-11 to panel 2-11-10.
Panel 2-3-11 is nearly a right triangle: Timoshenko has the formulae for a right triangular plate with two supported sides. Here too you could come up with a required thickness to start with some figures. BTW I don't think that your proposed rib would be very useful, unless you have loads on the edge (that you don't).
This structure doesn't seem so difficult, though it will require lengthy calculations. At a first sight it appears more or less stable, without requiring moment connections anywhere. Of course the free corner 16 need be analyzed firts for feasibility as above.
prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes for fun rides
http://www.levitans.com : Air bearing pads
RE: Another Tricky Question
He must sleep. This is his latest nightmare. I'll bet he sleeps in a "canopy" bed.
WpgKarl,
It might not be too bad for a hand calculations kind of guy. I don't believe it ought to be done by FEA. It is essentially a folded plate type of structure.
Gravity loads should be fairly straightforward. Wind loads would be tricky if this is outside. But I assume it is inside, right?
I would try to get more support for nodes 11 and 16. They appear to be flapping in the breeze.
BA
RE: Another Tricky Question
Never, but never question engineer's judgement
RE: Another Tricky Question
Never, but never question engineer's judgement
RE: Another Tricky Question
LOTS of weight, no tension resistance, no "assistance" across the pivot points (joints) from panel to panel .... And not really very pretty: concrete is about as drab and generic as you can possibly get = rather ugly ordinary typical government-paid-for urban "art" at its Euro-kulture worst.
So, if the arch. needs to paint the concrete anyway, why not use a lighter fiberglass or plastic "foam-filled" panel? The wind loads, snow and ice loads are the same, but the deadweight loads are 1/10 as much. The panels aren't going to be "sidewalks" or "bridges" that need to resist live loads - other than vandals or skateboarders.
RE: Another Tricky Question
Of course the pointy node 9 will get crushed - we would square it off a bit. The open part is about 10 ft high and is a storage closet.
racookpe1978: "And not really very pretty: concrete is about as drab and generic as you can possibly get = rather ugly ordinary typical government-paid-for urban "art" at its Euro-kulture worst."
Awww, c'mon, concrete is beautiful!
RE: Another Tricky Question
Decide on the thickness of the wings (or plates) - but make them all a uniform thickness, or vary the thickness of each based on the twisting load. Make each plate out of C channel frame (C3 or C4 inch if you have to, the smaller sizes will be prettier and "lighter" in appearance. TS2-1/2x2-1/2 or TS3x3x1/4 would also work, but doesn't surround the edges of the concrete as thoroughly.
Weld 3/8 or 1/2 rebar across the fame between the channels or TS members to make a web - wire mesh won't be stiff enough. Add a few diagonals for rigidity. Lay on a smooth form and pour: Use as light a aggregate as possible. The wings and panels are now stiff.
Your problem now becomes attaching (welding) the wing edges together with enough bead in enough length to resist bending. Paint the steel, whitewash the concrete, hang the architect ... You're good to go.
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For the far wall - consider vertical doubletees cantilevered from the ground.
Be extremely careful with how you detail the welded connections. The exterior exposure will require stainless steel connections. For the cantilevered beams I suggest NMB splices or sim.