Concrete Formwork Design Question
Concrete Formwork Design Question
(OP)

I have to check the following concrete formwork layout. It is to be used for walls and footings. All the studs, braces and wales are 2x4's and the sheathing is 3/4" plywood. I have checked the wales and studs for bending and the braces for compression and they seem okay but I can't figure out how to check the plywood. Is there any chance of the plywood failing? The formwork is only 5 feet high but the spacing is 3' wide.
I have been looking at the ACI formwork guide but I can't figure out what they are doing. Can someone explain to me what "Rolling Shear" is? Is there any chance of the plywood failing in shear? would this be a "blowout"?
Please see attached sketch for reference.
Incase the image doesnt work: Wale (vertical) spacing is 2.5', the stud spacing is 3'. The design does not use ties but instead 3 braces at different angles per stud.
Any help would be much appreciated!!! Thanks!






RE: Concrete Formwork Design Question
If you can live with that, you should be ok. However, I always use ties and 24" max spacing with 3/4 inch ply and 2x4 walers.
Mike McCann, PE, SE (WA)
RE: Concrete Formwork Design Question
RE: Concrete Formwork Design Question
Plywood has an odd number of layers. To get best performance (shear, rolling shear, moment, deflection) orienting the face grain perpendicular to supports (wales) will align the maximum number of layers in the correct direction.
Rolling Shear: The alternating layers of wood that are glued together to form a sheet of plywood guarantee that some of those layers will be positioned in the worst possible way. In the layers that are perpendicular to the horizontal shear the fibers tend to "roll" over each other.
I have not performed any calcs on your sketch, however, the plywood is overloaded. It probably won't actually fail but the results won't be "pretty".
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RE: Concrete Formwork Design Question
I will lower the spacing to 24".
How do I calculate the maximum moment on the wales when there is a non-uniform load? In this case the lateral pressure of the concrete. I can't figure out the load (w) is for Mmax=(wL^2)/10
RE: Concrete Formwork Design Question
www.PeirceEngineering.com
RE: Concrete Formwork Design Question
RE: Concrete Formwork Design Question
www.PeirceEngineering.com
RE: Concrete Formwork Design Question
RE: Concrete Formwork Design Question
My copy is the fourth edition and was published in 1981 as the revised second printing.
There is probably an updated edition.
Mike McCann, PE, SE (WA)
RE: Concrete Formwork Design Question
8th Edition of SP4 was published in 2014.
RE: Concrete Formwork Design Question
"Formwork for Concrete"
https://www.google.com/?gws_rd=ssl#q=formwork+for+...
Seems pretty complete.
However, no design like you propose, which may indicate my warning above is correct. I hate to imagine the unholly mess when the form gives way.
RE: Concrete Formwork Design Question
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RE: Concrete Formwork Design Question
Five feet tall isn't the tallest form in the world, but you don't want your form to slide an inch into the site either.
"We shape our buildings, thereafter they shape us." -WSC