40 foot round tank cover ideas
40 foot round tank cover ideas
(OP)
Got an interesting job and I'm interested if anyone has any good concepts on how to approach this.
Client has a 40 ft diameter concrete tank with an arched steel dome over it and is looking to replace the dome. The cover has to take large snow loads (~70 PSF ground snow) plus pedestrian loads. They got a price for an aluminum dome and it's fairly high so they're shopping around for alternative support structures.
So, I'm trying to come up with clever ways to do a precast structure that can be cost effective. We have a prestressing bed for slabs and small beams but it's limited to 18" depth. Any precast structural system ideas you folks think I should look at?
This is sort of the concept I was most leaning towards:
Client has a 40 ft diameter concrete tank with an arched steel dome over it and is looking to replace the dome. The cover has to take large snow loads (~70 PSF ground snow) plus pedestrian loads. They got a price for an aluminum dome and it's fairly high so they're shopping around for alternative support structures.
So, I'm trying to come up with clever ways to do a precast structure that can be cost effective. We have a prestressing bed for slabs and small beams but it's limited to 18" depth. Any precast structural system ideas you folks think I should look at?
This is sort of the concept I was most leaning towards:
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com






RE: 40 foot round tank cover ideas
RE: 40 foot round tank cover ideas
Without a post, I was thinking taking tapered panels up to a peak and installing a tension ring around the tank (assuming the current dome/tank doesn't already have something similar installed).
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com
RE: 40 foot round tank cover ideas
RE: 40 foot round tank cover ideas
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com
RE: 40 foot round tank cover ideas
RE: 40 foot round tank cover ideas
Is it necessary to create a positive drainage slope within the precast?
I've sketched a few options below. Your alternative would likely be preferable with respect to shipping, erection, and ease of drainage slope creation. Pretty much everything really. That said, you indicated that you wanted some options. I take that to mean more than one.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: 40 foot round tank cover ideas
A center column was not objected to by the client so that greatly simplifies things. It appears their only concern is cost and durability, all other concerns appear secondary. From what I gathered the cost being too high means that the project might just stall as they probably wont get funding from the city for a major project at this time.
Apparently waterproofing the tank is required; we typically use a butyl rubber sealant in a shiplap or keyed joint between precast sections. It's been accepted before for wastewater jobs for this city where it's not in direct contact with the sewage. That's a good question about the positive drainage KootK, I'll have to find out about that but I suspect we will need some small slope.
I looked at simple span slabs and it would be too expensive to ship. Your idea of a dapped beam could work, plus it doesn't all have to be precast. I could see a galvanized steel truss or something similar being acceptable down the middle and then precast panels spanning up to that. Thinking out loud though; anything that doesn't involved repetition always costs more with precast so I'd like to keep it as repetitive as possible.
Lastly, your "weird" slab panel idea looks crazy awesome. While I'd love to build it I have no idea how we would get these down the road without making every commuter in the state hate us. Though... do you have a CH-47 Chinook laying around I could borrow? :P
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com
RE: 40 foot round tank cover ideas
RE: 40 foot round tank cover ideas
"do you have a CH-47 Chinook laying around I could borrow? :P "
I actually checked into this years ago. The local helicopter company had about a 5,000 lb limit on their machine. To lift anything heavier, they had to fly a helicopter down from Kansas City, and that would run around $50,000 if I remember right. But the major obstacle was that they weren't allowed to lift a load and then carry it over people, so you couldn't just pick up an arbitrary (oversized) load and fly it to the far side of the metroplex.
RE: 40 foot round tank cover ideas
And, yes, I was definitely kidding about "playing with the contractor". I'm all for trying new and different but only when a clear path forward exists and there is a good chance savings can be realized.
Interesting anecdote about the helicopter. I always assumed it to be some astronomical cost but I imagine if you had a low-ish weight piece and the issue was the cranes reach or lack of access, then I could definitely see a helicopter actually being a practical way to set something. Probably not precast concrete though, darn stuff is usually quite heavy.
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com
RE: 40 foot round tank cover ideas
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: 40 foot round tank cover ideas
Then again, precast gets you better quality control and clear cover requirements. Plus the prestressing can save you a lot on weight which might become important if the walls aren't able to support a heavy concrete slab.
So, maybe you're right; maybe not. We'll submit our price and let the owner decide.
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com
RE: 40 foot round tank cover ideas
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: 40 foot round tank cover ideas
As for the pie slices, that appears to be the way to go right now. It's doable in precast, ship-able, cost effective, wont be the hardest thing to set, and should go very quick once we've finished fabrication. Only other thing I think that could derail this is if the tank walls/foundation can't support the panels weight.
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com
RE: 40 foot round tank cover ideas
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: 40 foot round tank cover ideas
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com
RE: 40 foot round tank cover ideas
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: 40 foot round tank cover ideas
"Very galvanized", hah! I don't know when but I'm going to get those exact words on a drawing one day.
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com
RE: 40 foot round tank cover ideas
RE: 40 foot round tank cover ideas
RE: 40 foot round tank cover ideas
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com
RE: 40 foot round tank cover ideas
RE: 40 foot round tank cover ideas
RE: 40 foot round tank cover ideas
We finished our estimate at $55,000 delivered cost so we're $20,000 cheaper than what they were quoted for an aluminum tank dome. Obviously some things aren't 1:1 as we'll need a bigger crane to set our pieces versus the aluminum dome.
Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com