How to calculate formwork for columns
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Formwork is needed to support vertical concrete forms such as columns, pillars, posts, shafts, struts and walls.
For square or rectangular forms, calculate the perimeter of the base and multiply it by the height.
For round or elliptical columns, calculate the area by multiplying the circumference (2πr) by the height.
If you're making any home improvements involving concrete, you're going to need formwork to hold it in place while it hardens. Knowing how to calculate formwork will make sure you order enough materials and can budget your project more accurately.
Follow this guide to find out how to measure formwork you need. If you don't want to calculate formwork yourself, you can hire a professional formwork estimator to take care of it.
Find out more: What Is Formwork?
While you'll be ordering concrete by volume, formwork is measured by area. Specifically, the area that will actually be in contact with the concrete. This means calculations will be in square meters (or square millimetres if more accuracy is needed).
To measure the area of formwork needed to support your concrete installation, multiply the perimeter or circumference by the length/height of the structure. Each side of concrete will need its own formwork calculation and more complex or irregular shapes will have more complex calculations.
If you're laying a concrete path, driveway, foundations or other base or flat surface, you only need to know how to calculate formwork area.
· For simple square and rectangular forms, simply multiply length x width to know how much formwork you need.
· For a circular base, multiply the square of the radius by pi (πr²).
· For irregular shapes, break these down into simpler squares and rectangles and add up the total surface area.
Formwork is needed to support vertical concrete forms such as columns, pillars, posts, shafts, struts and walls.
· For square or rectangular forms, calculate the perimeter of the base and multiply it by the height.
· For round or elliptical columns, calculate the area by multiplying the circumference (2πr) by the height.
If you're making formwork yourself, plywood supported by a lumber frame is the most economical option, but this won't be an option for round or irregularly shaped columns. These require metal formwork, which may need to be installed by a professional.
Formwork for concrete beams, girders and other horizontal forms should only be fitted on three sides, with shuttering supporting the two vertical sides and the bottom face. The top face should be left exposed.
Add the lengths of the three sides, then multiply by the span of the beam to calculate the formwork area needed.
Square and rectangular beams and girders may be made from plywood supported by lumber or metal. Round formwork should be made from metal.
For an example of how to calculate formwork for columns, let's say you need to estimate formwork for square concrete posts measuring 0.2m in length, 0.2m in width and 3.0m in height. The formwork uses plywood shuttering measuring 1.2m x 2.4m supported by a lumber frame.
To estimate how much plywood formwork you need to buy, you need to multiply the perimeter by the height to get the surface area needed for one column, then multiply this by the number of columns you need. Finally, you need to estimate how much plywood this would take.
Calculate the perimeter by adding the lengths of the four sides (a, b, c, d) and adding an extra 0.2m for overlapping of joints.
In this example, the calculation is:
Perimeter = a + b + c + d + 0.20
Perimeter = 0.2 + 0.2 + 0.2 + 0.2 + 0.2
Perimeter = 1.0m
Multiply the perimeter by the height of the column to get the surface area of the plywood shuttering.
Area = Perimeter x height
Area = 1.0 x 3.0
Area = 3.0m²
Let's say you're building 8 columns. The total area of all the concrete columns will be:
Total area = Area x number of columns
Total area = 3.0 x 8
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Total area = 24m²
Calculate the surface area of the size of plywood you're using. This example uses 1.2m x 2.4m plywood.
Plywood area = length x width
Plywood area = 1.2 x 2.4
Plywood area = 2.88m²
Divide the total concrete surface area by the surface area of one piece of plywood. This tells you how much plywood you need to buy.
Plywood needed = Total area / Plywood area
Plywood needed = 24 / 2.88
Plywood needed = 8.333
This means you'll need to buy 9 pieces of 1.2m x 2.4m plywood along with suitable falsework for support.
The difficulty of how to calculate formwork largely depends on the shape of the concrete form you're supporting. While a square or rectangular form will be straightforward to calculate and suitable for modular formwork, round or irregular forms may be more challenging and needs to be custom made.
If formwork can be reused on the same project or on future projects, this will lower the overall cost. However, the measurements need to be precisely the same each time. Metal formwork can be reused multiple times, but wooden formwork may not stand up to reuse, especially over long periods.
Find out more: How to Remove Formwork
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Measurements of concrete formwork (shuttering) is required for payment to the contractor for the concrete work completed. The payment to contractor depends on whether the cost is included with the concrete construction per unit quantity or formwork is paid separately, as mentioned in the conditions of contract.
The formwork is measured in terms of area that is in contact with the concrete surface.
Parts of Formworks for Beams and SlabsFor example, the formwork for concrete footing will be calculated as the surface area of four sides of foundation only. Bottom of the footing is resting on earth, there is no need of any formwork and top of footing is open.
Plan and Elevation of RCC FootingFrom the above footing plan and elevation, it can be seen that formwork area required will be
2 x (2 + 3) x 0.6 = 6 m2
Similarly, for a reinforced concrete beam, the measurement of formwork will be taken as the combined surface area of two sides and bottom of the beam.
Deduction of formwork area should not be taken for:
Units of Formwork Measurement
Formworks are measured in terms of area. So any unit such as square meter, square foot, square centimetre can be adopted. But generally, square meter and square foot of the contact area with concrete is taken as the unit of measurement.
The dimensions of a formwork should be measure correct to the centimetre or inches whichever the case may be.
Formworks are measured as just contact area, not area of formwork, as shown below:
Contact Area = 2h(L+B)The measurements of formwork are carried out separately for each type of concrete works such as following:
Read More:
Types of Formwork (Shuttering) for Concrete Construction
Plastic Formworks for Concrete &#; Applications and Advantages in Construction
Concrete Formwork Design Considerations &#; Basis for Concrete Formwork Design
Wooden Concrete Formwork Design Criteria with Calculation Formulas
Concrete Formwork Loads and Pressure Calculations
Concrete Formwork Removal Time, Specifications and Calculations
Formwork (Shuttering) for Different Structural Members -Beams, Slabs etc
Formwork Safe Practices Checklist
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