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Mswick 02-26-2010 08:59 AM

Round House Foundation Feasibility
 
Hello,

I am in a Technical Reporting class currently, and we are supposed to write a feasibility report on a construction project that was proposed by our instructor, then write about what should be done instead if we conclude that the project wouldn't work.

My section of the plan is the foundation. The proposed foundation is to have a concrete foundation which is in a "bowl" shape with a round concrete slab to cap it off. The inside of the foundation would be sealed and is proposed to hold rain water to use later. This foundation would be supporting a building that is a 30 feet diameter circle, with approximately 8 foot tall, 8" thick concrete external walls.

Similar to this:
http://i983.photobucket.com/albums/a...onProposed.jpg

Would this be a feasible foundation for such a building? The main area that I would be concerned with is that there are no vertical walls to hold the foundation solidly in the correct position. Would a better solution be to create a foundation similar to traditional foundations except in a round shape to fit the house better?

Something like this?
http://i983.photobucket.com/albums/a...ationRound.jpg

Any help would be appreciated,
Thanks, Mike

Bondo 02-26-2010 10:10 AM

Ayuh,... Plan B would work better than plan A,...
With the right loads,+ the right subsoils, Plan A foundation would simply Roll over....

HooKooDooKu 02-26-2010 10:11 AM

Two thoughts to toss out:

1. Do all swimming pools have flat bottoms?
2. What's providing support in the center of the building?

The 2nd question could also be rephrased as "How much load can the center of the building support?"

Just though of a 3rd thing to consider.
3. How are you going to build it?
I know there are standards for how to build flat concrete slabs and strait concrete walls. I'm not sure what standards there are for trying to build a bowl.

Mswick 02-26-2010 10:58 AM

Thank you both for your replies. I figured a design similar to the second one would be better.

As for support near the center of the floor, what would you suggest? Would a center pillar be adequate or should it have some sort of interior wall structure to give a more broad coverage of support?

We are not really looking into the standards for building it and the method of which it should be built, we are just looking to see if it would be feasible.

Thanks again,
Mike

HooKooDooKu 02-26-2010 11:10 AM

Quote:

Originally Posted by Mswick (Post 406234)
We are not really looking into...the method of which it should be built, we are just looking to see if it would be feasible.

Well now if there isn't a way to build it, then it's not very feasible is it?

Mswick 02-26-2010 11:14 AM

Quote:

Originally Posted by HooKooDooKu (Post 406242)
Well now if there isn't a way to build it, then it's not very feasible is it?

You're saying there would not be a way to build the second idea?

HooKooDooKu 02-26-2010 11:20 AM

Quote:

Originally Posted by Mswick (Post 406234)
As for support near the center of the floor, what would you suggest? Would a center pillar be adequate or should it have some sort of interior wall structure to give a more broad coverage of support?

Now isn't that a part of your homework assignment? To propose how to design such a structure?

After all, it is possible to build a concreate floor just as you have it drawn. But such a structure isn't going to be able to support as much of a load in the center of the building compared to the edges. Make the concrete too thin, and it can collapse under its own weight. Make the concreate too thick and it becomes cost prohibitive.

So you have to think through the requirements. The only one that comes to mind is what I've seen in floor joist span tables for residential construction. I don't recall the exact numbers, but I seem to recall that buidling standards (for residential construction) might be that a floor be designed to hold 10 pounds per square feet of dead load (the building structure) and another 40 pounds per square feet of live load (what you put into the house). And then the floor has to be strong enough such that the floor doesn't deflect more than 1/120th the width of the room.

So as an example, if you had a 10' wide room, the floor needs to support a total of 50 pounds per square feet without the floor deflecting more than 10' / 120 = 1".

Again, I'm not sure of the numbers, especially for comercial construction as compared to residential construction. But I point it out as a concept that must be considered in designing any structure.

HooKooDooKu 02-26-2010 11:24 AM

Quote:

Originally Posted by Mswick (Post 406246)
You're saying there would not be a way to build the second idea?

I was refering to the 1st idea mostly. While there might indeed be an industry standard for building a bowl out of concreate, if there is, I'm not aware of how you would do it.

On the other hand, when it comes to making flat surfaces with concrete, you simply build a form and pour the concrete in, smooth the top and you're done. But a bowl shape would have much more involved that that simple procedure.

Even in the 2nd example, if you do indeed need round walls, it's still going to be a bit more difficult than something with flat walls. Forms are usually made with wood. It's not too difficult to build squared wooden forms. It's not impossibe to bend wood to make round forms, but it does take more effort.

Mswick 02-26-2010 11:39 AM

Quote:

Originally Posted by HooKooDooKu (Post 406249)
After all, it is possible to build a concreate floor just as you have it drawn. But such a structure isn't going to be able to support as much of a load in the center of the building compared to the edges. Make the concrete too thin, and it can collapse under its own weight. Make the concreate too thick and it becomes cost prohibitive.

So you have to think through the requirements. The only one that comes to mind is what I've seen in floor joist span tables for residential construction. I don't recall the exact numbers, but I seem to recall that buidling standards (for residential construction) might be that a floor be designed to hold 10 pounds per square feet of dead load (the building structure) and another 40 pounds per square feet of live load (what you put into the house). And then the floor has to be strong enough such that the floor doesn't deflect more than 1/120th the width of the room.

So as an example, if you had a 10' wide room, the floor needs to support a total of 50 pounds per square feet without the floor deflecting more than 10' / 120 = 1".

Again, I'm not sure of the numbers, especially for comercial construction as compared to residential construction. But I point it out as a concept that must be considered in designing any structure.

Thank you very much for this, it is very helpful. I will definitely be taking that into account when I write my report.

Another consideration that I was thinking about was to change the floor material to wood instead of concrete. This will reduce the weight of the slab on top of the foundation and I believe it should be easier to construct. The way the teacher proposed this be constructed is to build the foundation and then using a crane, drop the preformed concrete slab over the foundation. According to some numbers I found online, the weight of the slab would be approximately 71,000 lbs. That would take a beefy crane to lift it into place. So constructing a wooded floor would be easier in my opinion. Am I totally wrong in this assumption?

Thanks again,
Mike

HooKooDooKu 02-26-2010 12:06 PM

To support lengths to 30', your talking about getting into building trusses or construction timbers (i.e. logs).

Dimensional lumber availability start to dwindal get above 16' lengths.

Mswick 02-26-2010 12:09 PM

Quote:

Originally Posted by HooKooDooKu (Post 406271)
To support lengths to 30', your talking about getting into building trusses or construction timbers (i.e. logs).

Dimensional lumber availability start to dwindal get above 16' lengths.

What if I was to use a center column that the supports tie into? Then I could use timber that is a little under 15' (foundation is 30' OD). Then I could put vertical supports at spaced intervals throughout the ~15' timber supports.

nap 02-26-2010 12:19 PM

either system is easily built.

for why you don't build #1; think Tower of Pisa (but even that has a flat based foundation)


#2. Without a lot of additional info such as size, cost constraints, floor loads, foundation loads, soil composition, building design, and many other bits of info, it is simply impossible to determine what would work for you. Way too many variables to even start a design.

Mswick 02-26-2010 12:35 PM

Quote:

Originally Posted by nap (Post 406277)
#2. Without a lot of additional info such as size, cost constraints, floor loads, foundation loads, soil composition, building design, and many other bits of info, it is simply impossible to determine what would work for you. Way too many variables to even start a design.

Here's what we were given. 30' OD circle, exterior walls of house 8' tall, 8" thick constructed of concrete (approximate weight without considering windows and doors, ~74,000lbs), houses family of four, interior walls made of very light material (something like Japanese paper walls), cost is not really an issue, just keeping it as low as possible, soil consists of an above average amount of sand. That's all we were given.

HooKooDooKu 02-26-2010 12:37 PM

Quote:

Originally Posted by Mswick (Post 406273)
What if I was to use a center column that the supports tie into? Then I could use timber that is a little under 15' (foundation is 30' OD). Then I could put vertical supports at spaced intervals throughout the ~15' timber supports.

Yea, that sort of thing is doable, but then why was a flat disk with only outside supports proposed?

Willie T 02-26-2010 12:50 PM

1 Attachment(s)
Why are you trying to reinvent the wheel?

See the picture of a water tank under construction.


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