What is Formwork?
Formwork is a temporary structure or a mould to cast the concrete or other material for getting the required shape and size, assure strength, and facilitate monolithic construction.
As the nature of concrete, fresh concrete is in slurry form, which gets harden after undergoing chemical change (hydration). Hence to get the proper shape of members like column, slab, and beam formwork is required.
Formwork can be divided into 2 parts, Centering and Shuttering.
The main components of the formwork include the column and main bearer. The bearer is a horizontal member to bear the load from several formwork bearers to pass off to the column.
The members of formwork which are used to support vertical and horizontal member of the formwork are known as staging. Props, bullies are examples of staging. Timber or steel tubes are generally used to provide formworks.
Also, one should be clear on the fact that the components of the formwork depend on either we are performing formwork for the wall or foundation, or any other. The shape and orientation of sides depend upon how well the formwork has been done.
Requirements of Good Formwork
- The material used in the formwork should able to resist the pressure of placing and compacting the concrete.
- The joints should be well connected that, there is no leakage.
- Formwork should be rigid enough to resist any deflection on the member.
- Members of the formwork are to be arranged purely mutually perpendicular, to produce a structural component of approved size.
- Formwork should be easily removable after the concrete gets harden, therefore should be arranged in a sequence.
What is Centering and Shuttering?
Centering is a horizontal Formwork whereas Shuttering is a vertical Formwork. For an instance, in a building, formworks for columns, walls, and sides of the beam are examples of shuttering and the bottom of the slabs and the beam are examples of centering.
Centering and Shuttering is a crucial part of the construction. The slab floor should be perfectly horizontal for the purpose to give a good working surface and to transfer load uniformly.
The column should be perfectly vertical to avoid eccentric loading. Also, the inclined member generates a moment that is not incurred in the designing phase.
Equipment’s used for Centering and shuttering
- Ply Boards/Panels
- Adjustable Props with base plate
- Acrow Span
How is centering done?
Centering is done for slab and beam soffits. 3-layer thick waterproof plyboard is used in general. Before casting a mould, the strength of the material and check for damages is performed.
- The horizontal members should be of uniform thickness and properly oiled.
- Plates should be perfectly horizontal and at a right angle with the vertical members.
- Gaps between the plate are to be filled.
- Staging is provided on the interval of about 600 mm center to center.
- The height of the staging is adjusted accordingly and bracing is to be provided at 4 feet from the ground.
- Staging should be rigid enough not to allow deflection.
- The depth of the beam and slab to be cast are to be clearly marked.
- Stripping time for the slab is at least 3 days and for the beam is 7 days but the props are to be removed only after 14 days for a span of 4.5m.
- Repairs are to be done if any damages occur, as soon as possible.
How is Shuttering Done?
There are certain things that need to be considered while performing shuttering work. Before the work to be started, what kind of material to be used needs to be checked, if any damages in the materials or found disfigured they should be thoroughly repaired.
- The inner side of the vertical members is oiled to ease the stripping process.
- The members are clamps together with the help of walers or knot- bolt. Walers are used in about 600 mm center to center distance.
- The walers are used to avoid buckling while pouring the concrete and to resist the pressure exerted on the shuttering members.
- Inclined members are also needed to make stand the member vertical.
- In the case of columns, they should be aligned, which is generally checked by a stretching string.
- The dimension and cover distance should not be compromised, and
- A Plumb bob is used to check the vertical alignment of the member.
- The formwork should be rigid and leakage-free.
- After 16-24 hours of placing concrete, stripping can be done if OPC is used.
- The surface of the member along with its level line is checked.
- If any damages, repairs should be made by consulting site supervisor.
- If everything seems okay, the member is cured for at least 7 days.
Difference between centering and shuttering
|Centering is the horizontal component of the formwork.||Shuttering are the vertical components of the formwork.|
|Stripping time for centering, according to IS code 456 is 3 days for slab and 7 days for beam but the props are to be refixed till 14 days for a span less than 4.5m and 21 days for a span more than 6 m.||Stripping time for shuttering, according to the Is code is 16-24 hours.|
|Centering is supported by vertical props.||Shuttering are supported by inclined Props|
I hope this article on “Difference between centering and shuttering” remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Rukshana Shrestha
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