Question

# How to Calculate the Area of formwork required for a Beam?

How to Calculate the Area of formwork required for a Beam? Calculate the area of the formwork required for a beam of 2 m span and cross-section dimension of 400 mm x 200 mm?

### Where am I?

As per my knowledge, depth of the beam is always greater than the width, that's why 400 is taken as depth and 200 as width.

Formwork shall be measured in square metres as the actual surfaces in contact with the concrete

The formwork or shuttering quantity for the member is measured as per the code of BIS – IS 1200:1982, Part 5- Method of Measurement of Building and Civil Engineering Works.

1. Measure the four sides of column at base or in cross-section.

2. Calculate the perimeter of column base.

3. Measure the Colum height.

4. Multiply the perimeter of base and height of column to give the shuttering area of column.

Or other way, add all 4 sides and multiply it by height of column.

1. Take the cross-section of beam and measure the lengths of the two sides and base of beam.

2. Sum the three measurements.

3. Measure the span of the beam

4. Multiply the span length by sum of the three measurements (beam base two vertical sides) gives the shuttering area of beam.

The top side in cross-section of beam is not considered as it will be part of beam.

Or the other way, add the beam height(2 sides) and beam base and multiply it by beam length.

Other important factors to be considered while picking the shuttering quantities.

• Where formwork is required to be lined with wall board, hardboard, polythene sheet No deduction shall be made for openings up to 0.4sqm.
• No deduction shall be made for any opening/cutouts when slip form technique is used.
• Raking or circular cutting and rounded or moulded edges shall be measured in running meters. Moulded stopping shall be enumerated.
• Formwork to secondary beam shall be measured up to the sides of main beams, but no deduction shall be made from the formwork of the main beams where the secondary beam intersects it.
• Formwork to beam shall be measured up to sides of column, but no deduction shall be made from the formwork to stanchion or column casings at intersections of beam.

Calculation:

Cross section I terms of metres (400 X 200 mm) = 0.4 X0.2 m

Width and depth are given in cross section

Area of the framework = (2 X 0.4 X 2) + (2 0.4  X0.2) + (2 X 0.2)

= 2.14 m²

Result:

The area of the formwork is = 2.14 m².

Your first solution is correct as in the key. But I have one more doubt related to this question.
Usually, we take the first dimension as length/width.
Why we took 400 as depth in 400×200.[Why not 200 as depth??]
If I took 400 as width I got another answer and that option also in the options.
Can you please clarify that. Then i will be really thankful to you.

Area of formwork is the inner surface area of shutter.

Here i attached the solution of the problem. In the problem it is not clear that beam is continuous or not. So,  i do both of the calculation ( solu – 1 – beam consider as continuous, solu – 2 – beam not consider as continuous) For non-continious beam- ends area should be taken for calculation.

In solution, i do the calculation by taking width as 200mm and depth as 400mm.

Yes, you can take opposite of it. For clear and effective answer, question should tell about width and depth of beam clearly.

But, In usual(it is just a general practice, not everywhere this approach will be right) practice of design- we go for larger depth compare to width, for minimum deflection of beam.

So i solve it by using general approach. Hope your doubts are clear.

Thanks