If you read these two posts — how to calculate shuttering quantity for footing and how to calculate shuttering quantity for column, you’ve already got the idea of how to calculate shuttering quantity for beam.
However, if you didn’t get the point, here is the step-by-step process of…
Calculating Shuttering Quantity For Beam
Step-1: Calculate The Total Length Of Beams
For that, get the beam layout plan from your structural drawing book. That’ll look like the image below:
This is an example of a beam layout plan.
With that:
Get the length of all the beams.
That will look like this:
[Note: sometimes, you won’t get the dimension of beams on the Beam Layout Plan. In that case, look in the Column Layout Plan.]
Now calculate the total length of beams.
In our example, that is,
= 3 × 21′-6″ + 3 × 19′-7″ + 3 × 4′-11″
= 138 feet.
Step-2: Calculate Sheathing Materials
Sheathing materials wrap three sides of a beam. The top face is normally kept open.
You can use plywood or lumber as sheathing materials.
To calculate these…
First, Calculate the perimeter of three sides of the beam.
And, the formula is,
= 2d + b + 4
Where,
d = depth of the beam
B = breath of beam
And for the lapping of form joints, the constant value 4 is used.
So,
= 2 × 20″ + 10″ + 4″
= 54″ or 4.5′
Next, calculate the sheathing area.
The formula is,
= Perimeter of three sides of the beam × length of beams
= 4.5′ × 138′
= 621 square feet.
Finally, Calculate the number of plywood or lumber.
Here is the thing.
There are some commercial sizes of plywood or lumber available in the market.
The available commercial size of ½″ thick plywood is 3′ × 6′ or 4′ × 8′.
Let’s say you’ll use 3′ × 6′ plywood.
Then the area of a plywood board is,
= 3′ × 6′
= 18 square feet.
So, the required number of plywood boards are,
= Sheathing area ÷ area of a plywood board
= 621 ÷ 18
= 34.5 nos
Say, 35 nos.
If you want to use lumber instead of plywood, then the available sizes of 1″ thick lumber are 5″ × 72″ or 6″ × 72″.
Let’s say you’ll use 5″ × 72″ size. Then the area of the lumber is,
= 5″ × 72″
= 360 square inches or 2.5 square feet.
So, the required number of lumber for our sheathing area is,
= 621 ÷ 2.5
= 248.4 nos
Say, 249 nos.
[Note: If you’re constructing beams on the ground, these are called grade beams, you don’t need sheathing materials for the bottom of beams. In that case, you just need sheathing materials for two sides of the beam instead of three sides.]
Step-3: Calculate The Required Quantity Of Struts
Sheaths are nailed to 2″×4″ struts placed on 3-foot centers.
For calculating the quantity of struts…
First, get the required number of struts.
The formula is,
= (Total Length of beams ÷ Distance between struts) × 2
= (138′ ÷ 3′) × 2
= 92 nos.
Next, Calculate the total length of struts for both sides of beams.
The formula is,
= Number of struts × Length of a strut
= 92 × 20″ (Length of a strut is equal to the depth of the beam)
= 1840″
= 153′-4″ (12″ = 1′)
Say, 154 running feet.
Finally, calculate the length of struts for the beam bottom.
To hold the beam in its place, you need to use struts at the top of the props. And props are normally placed at 2-feet centers.
To calculate the struts for beam bottom, apply this formula:
= (Total length of beams ÷ Distance between props) × Length of a strut
= (138′ ÷ 2′) × 1′ [Length of a strut for beam bottom is normally considered as the width of the beam. Although the width of the beam in our example is 10″, you can consider it as 1 foot.]
= 69′
[Note: For grade beams, you won’t need sturts for beam-bottom.]
Here, the total length of required struts are,
= 154′ + 69′
= 223 running feet.
Step-4: Calculate The Required Quantity Of Props
Props are used at 2-feet centers.
The formula for calculating props is,
= The total length of beams ÷ Distance between props
= 138′ ÷ 2′
= 69 nos.
[Note: If you’re going to build grade beams you won’t need props.]
Summary:
The required shuttering quantity for our beams are:
- Plywood (3′ × 6′) — 35 nos or 1″ thick lumber (5″ × 72″) — 249 nos
- 2″ × 4″ struts — 223 running feet
- Props — 64 nos
That’s it.