how to build?

[tompapa]

Any architect types out there have an idea on where to look for various methods of accomplishing the construction of decks like this? It would be great to be able to do them out of cast concrete but I have no idea where to go for information on that. I've found a lot of dead ends on the internet. If anyone knows, I'd appreciate the guidance. Tom

[WendyWelton]

You'll need a structural engineer to design the support for a deck like that.

[tompapa]

Yes, I realize that but I thought I'd draw it like I want it and get the engineer to match things as close as he can. I'm really trying to get thin decks. If I can read up on the possiblities I can present that information to my structural engineer. I like the guy a lot but he's not the most creative person in the world so I'm guessing I'll have to look into the options.

[dstig1]

Not perfect as it is precast, but might give you a lead or some other ideas. The vendors vary locally, but here are a couple in the upper midwest. They can do some degree of engineering and have span tables on their sites.

http://www.spancrete.com/
http://www.molin.com/

I'd be real leery of that cantilevered section. Just ask these folks:

http://www.paconserve.org/fw-building.asp
Try the very bottom of the page...

[tompapa]

Thanks Dave. This is interesting stuff. I'll be delving into it tomorrow. I've read about the problems at Falling Water but I'm thinking technology must have improved since then and my canitlevers aren't anywhere near as radical as those. The decks are essential to the look though. Plus, I think it would be an enjoyable space.

[mbbailey]

There is a product called Lite-Deck that may give you a hint. The product is constructed over a temporary platform and forms a series of reinforced concrete beams 12" O.C. with about a 20' span for 40psi live load. The cantilever would still be the problem and you would probably have to use steel I-Beams for that purpose. Take a look at their web site to get a picture of how it is constructed.

http://www.litedeck.com/

[hawkmoon36]

Just from what I've seen over the years, I have just 2 words for cantilevered concrete decks. BAD IDEA

Most codes don't allow wood decking to be cantilevered much beyond 4' and the amount of steel needed for a concrete deck would be immense. I mean you could get fancy and go with autoclaved concrete which is quite light, but it has to be made off site and I think there are only a few places in the US that sell it.

[jerryc]

You may look into Post-tension slabs, or pan decking. These products are used for commerical buildings and parking structures. For a standing or walking deck both may work.
use both and you may get what you are looking for . Talk with you engineer.

jerry

[ChiefChris]

That's what Frank Lloyd Wright did here in PA at fallingwater....very low ceilings, but nice decks.

He cantilevered concrete with huge steel T shaped peices...although the house undwent major renovations in the 90's...it still works.

[hawkmoon36]

I remember reading something about FallingWater. How the engineer suggested a certain amount of steel in the decks and Wright turned it down. He put in double the amount of steel and they still sagged. It's known as "creep" in the structural world.

[Allen42acj]

Just thinking/playing..
Maybe some thing like this..

[sutcac]

As I recall from structures classes in architecture school, there is sort of the Goldilocks' porridge principle in re-inforced concrete. Too little is bad, and too much can be bad too. You have to have the steel "just right"

[Allen42acj]

Wood beams can be the same way.To big and they have to be bigger to hold their own weight..
Quantum mechanics is easier to understand..

[Joe Carrick]

The easiest and least expensive way to do this will be with wood or steel. It appears that you have a support designed about 8' back from the railing. If you taper the beams/joists you can cantilever 8' while still keeping the edge thin. The structural principle is similar to a retaining wall turned on it's side and you could do it with concrete, but the potential for the reinforcing to rust in the future is pretty high, since water will inevitably penetrate into the deck. When steel rusts, it expands to about 7 times it's original size and will break concrete from the inside.

If you use tapered wood joists or beams, you should be able to cantilever 8' with members that are tapered from about 14"-16" at the support down to 8" at the deck edge. Your structural engineer should be able to check this and figure out what sizes and spacing to use.

[hawkmoon36]

OR... you could just stucco the whole kit 'n kaboodle. LOL