Construction form work question.

[SF_century]

When estimating how much plywood needed for a retaining wall do we include plywood on all four sides of the retaining wall? Or do we allow the soil on the bottom and sides of the footing act as the plywood ?

 

[Dexman PE PMP]

For the sake of estimating walls & their footers, you assume forms for all vertical faces unless specifically noted otherwise.

Formwork includes the full wall face (front and back) as well as the bulkheads at the end. You do not place forms for the bottom or top (unless specifically noted). One other thing to keep in mind is the units. If they ask for total SF of formwork, you only calc the surface area of front, back, and ends. But if they as for "how many sheets of plywood" then you divide the total SF by 32sf and round UP to the next full sheet.

For example, a wall is 10' long, 5' high, and 6" thick. Total SF would be 10x5 (face) + 10x5 (back) + 2x5x0.5 (ends) = 105 SF. However, since plywood comes in 8'x4' sheets (32sf each), you would need 4 sheets (3.3 sheets, rounded up).

 

[John QPE]

Great explanation. Thanks

 

[SF_century]

Thank you!

 

[ptatohed]

Be prepared for the problem to provide an allowance for waste too.

 

[NJmike PE]

Be prepared for the problem to provide an allowance for waste too. 

This

 

[ThoroughPM]

You might also try and work an example of an elevated slab. There were examples in some of my exam study guides that would be a little different take but good practice.

 

[thechosenone]

Formwork at the ends: Does it mean if the wall is 10' High and 1' wide thick:

The formwork at the ends would be:

1'w x 10'H x 2 ends= 20 SF?

 

[thechosenone]

in the grand scheme, practically it would be negligible effect....

 

[desantmf]

Yes, you are correct with the above answer. That amount does matter on the test though. So make sure you account for all of it.

 

[Dexman PE PMP]

Formwork at the ends: Does it mean if the wall is 10' High and 1' wide thick:

The formwork at the ends would be:

1'w x 10'H x 2 ends= 20 SF?

The answer is correct.

The quantity may be negligible if the wall is significantly long, but it still matters because it adds a good portion of another sheet of plywood to the answer.

 

[SF_century]

Thanks to everyone for the help on this one!