I need details and specific information on how to properly erect a 15′-0″ in diameter half round concrete wall 8′-0′ high for my house project in Vermont. Please respond, thanks.
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Replies
is this an addition to an existing home ?
are you forming an entire house foundation ?
will you see the interior or exterior of the concrete ?
what will be the finish on the exterior wall of the structure ?
what is the wall thickness ?
carpenter in transition
Thanks for your inquiries. Yes it is new construction, and new framing, not much of the exposed conrete wall, will be exposed (12") at the exterior. The wall is 10" thick. We will be conc. parging the exposed conc. wall. Any other questions?
What has your designer/architect/engineer told you about it?
The wall is shown on the foundation plans with all the required size, radius and detail of all reinforcing. I need methods for construction.
Do you need to mono-pour or is a cold joint ok? What exactly are you doing?
my first thought is to cut the radiused walers from 3/4" CD plywood and line the form walls with wacky wood plywood. I dont know if wacky wood would hold the pressure of an 8' form wall. It depends on the thickness and the number of walers
Need more info
I would prefer a continuous (mono) pour in order to avoid water infiltration. I'm building a new home and have drawings, but need methods of construction.
what type of forms are you using to form the rest of the foundation ?
are you the GC ?
are you forming the entire house yourself ?
carpenter in transition
I'm not sure what type of forms are being used, I'm not the GC and I'm not forming the walls myself, I'm just trying to help the owner.
david is right, the cost of this is going to be extreme. at least 3x to 5x compared to a straight wall.
depending on the radius, we do this one of two ways. the first is with Symons panels sized in width with Symons assistance. this gets complicated in trying to get proper tie alignment from inside to outside. with this method, you don't get a true curve, you get a segmented curve.
the second method involves using common framing lumber to build your own forms. 3/4" plywood is used to make the top and bottom wall plates. 2x4 or 2x6 studs are used on 6" to 12" centers, depending on the radius to build the 8' tall walls. 1/4" plywood is applied to the walls in 3 layers with a final thickness of 3/4". again, depending on the radius, two layers of 3/8" plywood may work also. as Tom mentioned, snap ties are used to hold the wall to its 10" thickness. whalers are horizontal braces which are applied to the back of the framed wall to help keep its shape. in this case, the whalers would have to be made from plywood.
we used the second method to form 3 12' diameter cylinders for 12' fans in a commercial concrete cooling tower. the fan blades came within 1/4" of the concrete walls, so the tolerances in this case were extreme.
you can use a combination of the two methods with the standard Symons panels on the inside and custom forms on the outside. this can be done if you are concerned about a true curve only on the outside.
there are whalers which are designed for this purpose. they are metal, adjustable and are installed on custom framed walls without top and bottom plates. the whalers are adjusted after installation to create the desired curve. i have never used these, they are geared toward forming concrete tanks.
while curved walls look great, they have a very high cost. this cost doesn't end at the foundation. everything is more difficult, floor and wall framing, wall sheathing, window installation, siding installation, roof framing, roof installation. unfortunately, most of the time, the radius walls get deleted to save money.
carpenter in transition
Who is doing the foundation? A foundation contractor with panel forms?
You will need a talented form builder to even do a multi-segment corner, with a sequence of flats (think polygon) approximating the curve. Tying with snap ties is easy . . . bracing to fix in position and prevent blowouts is hard.
To do a truly curved wall segment, you'll need a talented form builder you might have to search real hard to find.
I built a house that needed this, but instead of curving the foundation wall, I did a couple 22-1/2 degree bends with flat segments, and made the wall 12 inches thick where it went around those bends, stopped the wall pour right up at grade, and then had my mason do a better approximation of the curve with hand-cut concrete block units above from there. We doweled the block part into the wall below, and filled the block with concrete, then did some serious waterproofing on the outside.
I work for a concrete form company in RI. That out of the way, it is feasable to produce your curved wall out of tee and wedge forms, I know because we did it, but it took 5 of us about 2 hours to set it. Like Stinger said, a lot of 22 1/2 degree panels. I wont post the specifics here because it might take a page or two, e-mail me for the whole story. But fear not, and concrete form company worth their panels should be able to produce that radius.
3/4" CDX ply with snap ties will work fine, but you're going to have some interesting walers. Likely need to kerf the CDX a few times, shallowly. Bear in mind that the inside and outside radii are quite different. Drilling for snap ties changes accordingly.
No window blockouts in the curve? That gets even more interesting. You have a much tighter curve, but here's my first attempt which had a parallel wall 30' from it. Keeping them parallel was challenging.
PAHS Designer/Builder- Bury it!
Thanks for your reply, I will send it to the owner
tom
are those round columns in between the windows ?
carpenter in transition
Yup. Sonotubes, or the equivalent. And no, they aren't particularly straight. Lots of steel in there to the point of being very difficult to vibrate. But other than not quite straight, they came out great.
Clearly, I like curves. This is our present home. Intended to be my future furniture shop. Plan has changed a bit, turned out to be worth too much as a rental. The new house is out of the ground, same curves, arches, and ceiling height. I'm exploring different shapes for a shop, a little down the mountain.PAHS Designer/Builder- Bury it!
Here you go. Not exactly between the windows. It's a thick wall. DW chose to have the large sill inside.PAHS Designer/Builder- Bury it!
impressive.
is that a horizontal cold joint at the window heads ? did you do two pours ? were the columns done with sonotube ?
carpenter in transition
Thank you Tim. The plan was for me to have an impressive place to hawk my (expensive) commissioned furniture. The site is probably even better. The replacement house will get finished someday. Meanwhile, there are worse places to live...
As this was my first ever concrete experience, having only read a how-to form book, I was very cautious. This was the only time I laid the plywood horizontally. These walls took 4 pours (4'+4'+4'+4') to get to the top. When I built a similar client house the plywood was vertical, 2 pours. Not much about concrete intimidates me any more.
Columns (7') were sonotubes. When I paid for my engineering I made certain to get as much education, in addition to the drawings, as I could. We covered a lot of territory quickly. The engineer was pleased that I had my questions in order. Prior to that, I'd done a lot of reading on the subject. And seen more than a few problematic foundations. One big question was about cold joints. Good place for a leak, but structurally not an issue, due to the rebar. There's a lot of rebar here.
I was running a cabinet shop for an upscale builder when I started this. Had no intention of doing my own concrete, but ran into a major problem finding somebody to do it here at the time. Pretty much everything was cmu. Solution was to be here full-time with a couple of guys who knew less than I did about concrete. Fast, we weren't, but it's here and nobody got hurt.
There's more at: http://paccs.fugadeideas.org/tom/index.shtmlPAHS Designer/Builder- Bury it!
Very few residential builders do stuff like this very often, so we make it up when we have to. A project like you are describing will be very labor intensive and very expensive, and somewhat experimental. Everyone will have a different way of going about it.
I think I'd buy several sheets of 1/4" plywood (CD or AC, depending on how you want the concrete to look. I would use the plywood vertically since you say the wall is 8' tall, and the plywood will bend more readily in that direction. Set up one layer and then set up another with a 2' offset between pieces. 3/8" might work too. I recently bent some 1/2" CDX and it would be tough on a 15' diameter, and 3/4" would be out of the question.
The walers are going to take some serious labor and a lot of wood scrap will be generated. Ideally you plan your forms so that lumber from the forms can either be reused in the framing, or reused for more forms later (i.e. if you are a concrete guy, which you are not).
I would probably plot out the entire thing, full scale, on a floor somewhere so that I could plan all of the necessary pieces and determine the sizes that will work. Maybe something like the attached pic. I think I'd try to avoid cutting a bunch of curved pieces.
An alternative would be to contact a commercial concrete contractor who does curved work. You see stuff like that in fancy downtown areas. There are curved metal forms they use, stuff the average person can't afford.
Thanks for your reply, I will inform the owner and make him aware of the possible higher cost.
horse .. we formed a 14' diameter half circle wall ( 8' high 12" wall ) using regular 12" form panels..
drove a rebar center stake to pull our radius off..
no sweat...Mike Smith Rhode Island : Design / Build / Repair / Restore
A faceted wall or a smooth radius.... do tell?
12" facets... since only 18" or so of the concrete is showing.. it turned out greatMike Smith Rhode Island : Design / Build / Repair / Restore
If 12-inch wide panels would result in a an effect that is too faceted for what you want, you could save a bundle by using actual lumber. 1X stock placed vertically, like barrel staves - and then you could use the stuff later for something else. Sounds like fun.
Are you familiar with formwork? If so read this post.If not ,hire someone who is familiar.Cut top and bottom plates out of 3/4" plywood. Use a router for best results. You have to cut two different radius, 15'-0 minus 3/4" for the sheathing.
Then if the wall is 12" thick the inside plates will be 14'-0 minus 3/4" for the plates again. The plates are doubled,arranged so the joints are spliced. You can eyeball or use a center square for the stud layout. The studs are 12" on center and nailed squared to the radius. This is where the plastic center square helps (any woodturning website will carry them)
I would use Gates ties , they work well for radius work. Ties are set up same as a straight wall,2'-0 centers horizontal , 2- 5/16" from the top and bottom. 15 -5/16" centers inbetween.
Walers are not needed, the studs are the walers.The studs are nailed flush with the plates you cut. Make each panel long enough to accomadate the sheathing. You may need to put two layers of 3/8" instead of one 3/4".Close up panels are made the same way .You need a lot of clear space to walk the ranel in, won't tilt like a straight wall.Plumb and brace as usual.
mike
Horse,
The key to this problem is the horizontal rebar radius.
For the purpose of explanation, I will assume that the 15' radius is the outside radius of the wall. The inside radius of the inside horizontal rebar will be 14' 3" ±1/16". The outside radius of the outside horizontal rebar will be 14' 9" ±1/16". The inner verticals must be in radial line with the outer 12" OC vertical rebar. Place two rows of horizontal rebar chords near the middle and top of the wall, such that each chord spans the outer rebar grid and touches the inner grid. This will prevent the grids from distorting from the pressure of the forms. Place 3" adobes on the horizontal rebar.
Create continuous panels of 1/4" ply to match the 14' and 15' radii + 4 1/4" for each endcap. Endcaps will be made of standard 3/4" ply and 2x4 framing. I suggest attaching ply sheets together with 1 1/2" metal strapping sandwiched to the ply edges with self tapping self drilling screws 3" OC. Place the screw heads on the outside of the forms so they can be removed before stripping the forms from the cured concrete.
Predrill the forms for the snapties. Use OC measurements like 15 X/Y (outer) and 14 X/Y (inner), where X/Y is a fraction of which a multiple of 15 aproximates 12" or 16" (15 x 25/32 = 11.71875" and 14 x 25/32 = 10.9375". Someone with a CM can convert that to 32nds for you. 15x 1 1/8 = 16 7/8" and 14 x 1 1/8 = 15 3/4") I suggest creating a table of dimensions so that measuring errors do not compound. Don't forget the 8 1/4" from edge starting dimension, (4 1/4 Endcap, 3" rebar to concrete face, and 1" clear to rebar.) When rebar interferes with a snaptie, new holes can be drill on the spot with a 15" drill bit.
Attach the endcaps to the inner form sheet, stand the sheet up to the rebar and push the center in towards the rebar. Attach 2 come-alongs to the endcaps and start tightening them to pull the form towards the final shape and to hold it in that position while you. . .
Attach the outer form to one endcap and place the first vertical row of snapties. Using 2x8 studs (Sidebar - standard snapties are sized for concrete plus a total of 2 ea 3/4 plys and 4 ea 2x4s or 15 1/2". 2 ea 1/4" plys and 2 ea 2x8s are also 15 1/2") clip the snapties in place. Repeat for the second vertical row of snapties , then check the tension on the come-alongs. Continue the length of the wall, always checking tension on the come-alongs every two rows of snapties.
When you are done the forms will be firmly forced against the adobes. Since this is a strongly curved wall, walers and plates will not be needed because of the circumferential tension and compression of the plywood. Adjust the come-alongs to keep the ends of the wall on line untill you get them braced.
SamT