hey, y'all.
my camp has a 32' diameter 4v dome that's been to the playa a few times. This year, we've built a sign to put on top of it. I'm curious what folks think about load bearing limits for domes.
The dome is constructed of 1" EMT.
The sign is approximately 4'x'4 in the shape of open lips (it has an opening to hopefully reduce it's wind load a little bit). It weighs roughly 80lbs.
Currently, my plan is to attach a 5 legged 'tripod' to the top pentagon of the dome, with a joiner plate at the top of the 'tripod' that the sign is bolted to. there's also a support that rises from the center point of the dome, to the bottom of the connector plate. I'll also have 3 guy wires from the top of the sign to lower points on the dome, to try to minimize sway. (if i've just confused you, i can try to draw it up later)
When I mocked it all up on just the top section of dome in the shop, it felt quite solid. I'm now just concerned about how it'll work on the playa, in the wind...
whatchaall think?
my camp has a 32' diameter 4v dome that's been to the playa a few times. This year, we've built a sign to put on top of it. I'm curious what folks think about load bearing limits for domes.
The dome is constructed of 1" EMT.
The sign is approximately 4'x'4 in the shape of open lips (it has an opening to hopefully reduce it's wind load a little bit). It weighs roughly 80lbs.
Currently, my plan is to attach a 5 legged 'tripod' to the top pentagon of the dome, with a joiner plate at the top of the 'tripod' that the sign is bolted to. there's also a support that rises from the center point of the dome, to the bottom of the connector plate. I'll also have 3 guy wires from the top of the sign to lower points on the dome, to try to minimize sway. (if i've just confused you, i can try to draw it up later)
When I mocked it all up on just the top section of dome in the shop, it felt quite solid. I'm now just concerned about how it'll work on the playa, in the wind...
whatchaall think?
posted by:
|
New York City
|
-
Re: weight on the top of a dome?
Wed, August 15, 2007 - 6:10 PMI'm not a structural engineer, but the weight is, in my opinion, not an issue at all. The only real issue is wind load -- sideward stress which might strain and break whatever mounting mechanism you devise. I think the sign itself is more likely to fail than the dome. I think you should add a redundant chain or cable to catch the sign in case its mounting completely fails and it would otherwise blow off the dome. A sign that large would easily kill someone if it flies off the dome. So, attach a chain or strong steel cable in such as way so it acts as a failsafe in case all else goes badly.
-
Re: weight on the top of a dome?
Sat, August 18, 2007 - 4:52 AMAs is becoming usual, I pretty much agree with Hoco <grin>
I have an approx 20' diameter 3v dome with 3/4" EMT that has had multiple people in sky chairs suspended from single vertices.
Hoco has some great advice RE your mounting mechanism. I agree completely.
On the weight issue I would like to add one caveat-- as the frequency of a dome increases, as it, say, gets closer to a sphere, (and/or as the hub mechanism gets less rigid/has more play in it) the vertices can "pucker" inwards. This is why Fuller's ginormous dome in the, was it Toronto? expo or worlds fair or whatever it was had to have two layers, with bracing in between.
So given that you have a higher frequency dome than the one I described above, you may be more prone to puckering vertices. Since you've had it out to the playa a few times, I reckon you have a pretty good idea of how prone your dome is to this effect, so keep that in mind.
Good luck and happy experimenting!
Bruce :-) -
-
Re: weight on the top of a dome?
Sat, August 18, 2007 - 3:53 PMthanks for the advice!
I am slightly nervous about the sign buckling, and am planning on having a few folks take a look at it before it goes up next weekend. I've got a perfectly acceptable backup plan, if I decide it's better to not risk the thing falling off the dome...
I think having the higher frequency dome could be a double edge sword... On the one hand, yes, it might be more likely to pucker the vertices (never thought i'd be saying that...). But, on the other hand, it might be less likely to crumple the dome under wind load... (the sign, on the other hand...)
I think adding the safety chain is a pretty good idea, as in a complete failure, it'll at least slow the sign down a bit, though i'm betting the shock load of the chain catching the sign would do a fair bit of damage itself.
Come by and see us, if you're going to be on the playa, we're Smoochdome, and will be near 3:00 and Arctic...
thanks! -
-
Re: weight on the top of a dome?
Sun, August 19, 2007 - 2:17 PMLet me add that installing the sign is liable to be the most dangerous part of your project. Even a small breeze will apply a lot of force to the sign and whoever is positioning it could easily be overwhelmed, given that they may be standing on ladders or on the dome itself. Perhaps it is possible to attach the base and then pull it up with ropes from the ground, and attach those ropes to the dome until the rest of the signs supports are in place.
Bruce is right about the higher V domes being more susceptible to buckling; however, they are also better at supporting weight and distributing forces throughout the structure. Your dome will be very strong. Just FYI, I made a 28' diameter 2v dome from 1" conduit and it was insanely strong. 1" conduit is at least 4 times stronger than 3/4" conduit, according to a structural engineer friend of mine (Tara of desertdomes.com, who would definitely know!) However, I don't think I'd be too concerned about buckling. Thunderdome is a 4v dome, and it often has people on every vertex and strut. Of course, it is steel pipe, not conduit, but if buckling was going to happen because of being a 4v with weight on it, it would probably have happened already.
We're neighbors, by the way. I'm in camp Nose Fish in the 3:00 plaza. Come by in the morning for espresso (courtesy of Espresso Camp) and biscotti (courtesy of my camp). -
-
Re: weight on the top of a dome?
Tue, September 11, 2007 - 10:48 AMFirst many props to Hoco and nosefish for all of your website contributions to the world.. I have been noodling the addition of a deck to the top of my dome and your design is a great help to that effort..
Second, I'm going to contact desert domes but in the interim does anyone know of a resourse for actualy calculating the live load bearing ability of a dome.. I have all of the specs on the conduit and bolts but I need to translate that into an actual live load strength for my deck so that I can then build in a safety margin and socially limit it's loading (through limited surface)..
Thanks for reading..
John -
-
Re: weight on the top of a dome?
Thu, September 13, 2007 - 11:46 AMSo, I did some practical experiments on my dome deck this year at Burning Man. At one point we had 815lbs on the deck and it worked fine. I figure it could handle 1000lbs and then failure would occur. Failure would most likely be bending of the struts in the top pentagon of the dome. Those five struts are under compression and as the weight goes up they will eventually bend. If they bend enough the deck will descend into the dome as the dome bends from convex to concave.
The solution would be to make those top five struts out of 1" conduit instead of 3/4" conduit. Then they would be 4 times stronger. I would still estimate the limit at 1000lbs but I wouldn't worry about collapse based on those struts. Some other struts would likely fail first.
I put up signs on my dome deck saying the limit was 600lbs or 4 people, and asked people to distribute their weight. I still think this is the right weight limit to post on a 2v optimal dome made exclusively of 3/4" conduit, even though I experimentally determined that the weight limit is higher. If one used 1" conduit for the top pentagon of the dome, I'd make a sign that says 750lbs or 5 people. I would not post a higher weight limit even if the dome could handle it, because people notoriously bend the rules and one must underestimate the limit to take that into account.
By the way, people loved the dome deck! There were people up there a lot of the time during the day. It was a lot of fun to sit up there during the dust and wind storms.
-
-
-
-
