Formwork: Learn its Definition, Components, Types and Removal Period here!

Formwork (shuttering) in concrete construction is used as a mould for a structure in which fresh concrete is poured only to harden subsequently. Types of concrete formwork construction depend on formwork material and type of structural element.

Formworks can also be named based on the type of structural member construction, such as slab formwork for use in a slab, beam formwork, column formwork for use in beams and columns, respectively, etc.

型枠

Formwork refers to the temporary structure used to support concrete until it hardens and becomes self-supporting. It plays a critical role in ensuring the accuracy, quality, and safety of the concrete construction process. Formwork can be made of a variety of materials, including timber, steel, and prefabricated panels, and must be designed to withstand the pressure of the concrete as it is poured and cured.

What is Formwork?

The construction of formwork takes time and involves the expenditure of up to 20 to 25% of the cost of the structure or even more. The design of these temporary structures is made for economic expenditure. The operation of removing the formwork is known as stripping. Stripped formwork can be reused. Reusable forms are known as panel forms and non-usable forms are called stationary forms.

Timber is the most common material used for formwork. The disadvantage of timber formwork is that it will warp, swell, and shrink. The application of water-impermeable cost to the surface of wood mitigates these defects.

Formwork Design and Layout

The design and construction of formwork must consider both safety and the required surface finish. The formwork must be rigid and tight enough to prevent cement slurry loss from fresh concrete or the formation of fins and honeycombing on the surface. IS 14687 can be consulted for more information on design, detailing, and so on.

Formwork and its supports keep their correct shapes and profiles so that the final concrete structure stays within the specified dimensional tolerances. They must be built to withstand the combination of self-weight, reinforcement weight, wet concrete weight, concrete pressure, construction and weather loads, as well as all incidental dynamic effects caused by placing, vibrating, and compacting the concrete. The reinforcement steel shall never be tied to or supported by the formwork.

All horizontal and vertical formwork joints on the exposed surface must be staggered in order for the joint lines to be visible. The size of such panels must be approved by the Engineer in charge before they are used in the construction of the works if the contractor proposes to make up the formwork from standard-sized manufactured formwork panels. The finished appearance of the entire elevation of the structure and adjoining structures shall be considered when planning the pattern of joint lines caused by formwork and by construction joints to ensure continuity of horizontal and vertical lines. 

Formwork Importance

• No doubt formwork is essential for any construction; its main advantage is that it can’t be replaced with any other technology.
• Using formwork, concrete structures can be constructed quickly and in the most affordable way.
• During all construction work periods, a formwork offers appropriate access and working platforms that considerably enhance workers’ scaffold safety.
• Formwork helps in lowering the timeline and costs of the project by lowering the floor-to-floor construction cycle time, which means more projects can fulfil their budgetary demands.
• Formwork facilitates construction managers to offer exact on-time shuttering and de–shuttering of formwork resources, which results in improving project effectiveness and resource usage.
• Formwork is mainly associated with concrete. It helps in producing a smooth finished surface of the concrete.
• It provides good structural safety by offering solutions against all overlay loads, producing exceptionally safe and practical structures.

Components of Formwork

The various components of formwork are shown in the figure below, and let us study them one by one. 

Fig.1. Components of Formwork

• Ties: A tie is a tensile unit used to connect opposite sides of formwork. It serves as a balanced connection or is used to resist the effective pressure of fresh concrete. 
• Braces: Braces are used to keep the formwork upright by deterring form deflection under lateral pressure.
• Studs: Studs in the formwork are used to support sheathing panels and make a framework to keep them in position. 
• Sheathing: Sheathing panel is used to keep the concrete in its required shape and position until it sets and hardens. 
• Wales: Wales are horizontal propping members that are placed against sheathing to directly resist sheathing pressure.
• Battens: Battens are vertical members in the formwork which keep cleats and wales uptight and in position.
• Footing: Footing is the bottommost member which supports the entire formwork.

Cost/Economy of Formwork

Construction of formwork takes much effort and also consumes up to 20 to 25% of the cost of the whole structure work. That’s why it is very important to keep it cost-effective parallel to its strength.

Here are some key points which can help reduce the cost of formwork.

• Try to reduce the variation in the building or structure design. It can help to reuse the shuttering again. And the way of reusing shuttering reduces its cost.
• Economical structure design can reduce the sections of structural members. Reduction of sections can help to fix less shuttering, as a result, costs can be reduced.
• Proper cutting of plywood and timber can also reduce the cost of shuttering.
• The use of the different engineered systems of form-work can reduce labour costs and save time but as per material. They are costly, initially, they are not reducing the cost of shuttering. But in large projects saving time can help to reduce the all-over project cost.

Requirements of a Good Formwork

• It is very important that the formwork is well supported and strong enough to bear all loads applied to it.
• Formwork must be aligned and braced well from all sides to keep its original shape.
• It should be watertight to prevent the leakage of cement grout.
• It should be constructed in a proper way so that at the removal stage concrete can be safe.
• The form-work material must be available locally, cheap, and can be used more than one time.
• Try to keep it lightweight as possible to prevent the extra load on supports. Especially in horizontal shuttering, lightweight formwork also can help to reduce labour costs or effort.
• It must be fixed in line and levels as per the drawing.
• Form-work material should not be damaged or rusted, which affects the quality of concrete finishing.

Types of Formwork

There are several types of formwork used in construction. They are discussed below in detail. 

Timber Formwork

Timber formwork is the most common type of formwork among all others. Timber forms are extensively used in construction since the ancient period. Timber formwork is the oldest type of form used in construction.

Timber formwork is one most used in construction among all other types of formwork. It offers onsite fabrication of the required shape and size. It is easily used in any construction but it may prove time–consuming for large projects. Plywood formwork material has a short lifespan. Timber Shuttering is low-cost and easily workable shuttering. It can be cut and joined in any shape and size.

Fig.2. Timber Formwork

Requirement of Timber Formwork

• Light in weight
• Properly seasoned
• Free from any termite attacks
• Easily workable

Advantages of Timber Formwork

• Timber Shuttering is easy to form any shape, size, and height.
• It is proven economical for small projects.
• It can be made using locally available timber.
• Timber is light–weighted compared to steel or aluminium shuttering.

• Column Formwork

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Steel Formwork

Steel formwork has become more popular due to its strength, durability, and repetitive reuse for a long period. Steel formwork is costly for small work but can be used for a large number of projects. Steel shuttering offers a smooth surface finish to concrete compared to timber formwork. It can be used for circular or curved structures such as tanks, columns, chimneys, sewers, tunnels, and retaining walls.

Fig.3. Steel Formwork

Advantages of Steel Formwork

• Strong, durable and longer life
• It offers a smooth finish to the surface of the member.
• It is completely waterproof or moisture–proof and minimises the honeycombing effect.
• It can be reused more than 100 times.
• Steel formwork can be fixed and removed with greater ease.

Aluminium Formwork

As we know the density of aluminium is less compared to steel and that makes it light-weighted than steel. This is the main advantage when compared to steel. Aluminium formwork is almost the same as formwork made from steel. Shuttering down with aluminium form is proven economical if large numbers of repeating usage are made in construction. Its major drawback is that no alteration is possible once the formwork is constructed.

Fig.4. Aluminium Formwork

Plywood Formwork

Plywood formwork is one of re-moulded timber resin-bonded plywood sheets attached to timber frames to make up panels of the required sizes. It is strong, flexible, and easy to handle. Its life is too short compared to other materials.

Fig.5. Plywood Formwork

Fabric Formwork

With the advancement and new technology trends in building planning and designing, the construction of complex–shaped structural members is increased. To satisfy this need the fabric formwork is introduced which makes the flexibility of this material make it possible to produce concrete in any shape. The flexibility of fabric formwork makes it possible to produce concrete members of any shape.

Fig.6. Fabric Formwork

Plastic Formwork

Plastic formworks are lightly weighted, interlocking systems and can be used more than 100 times. It can be used for normal concrete construction. This type of formwork is now becoming popular for similar shapes and large housing schemes.

Fig.7. Plastic Formwork

Advantages of Plastic Formwork

• Plastic forms are light in weight and hence require less handling cost.
• It can be utilised in the large concrete section.
• If careful installation and use, multiple reuses are possible making it highly economical.

Formwork for Column

Formwork for columns is an essential part of the construction process, providing temporary support and containment for the concrete until it sets and gains sufficient strength.
1. Panels: Large, flat surfaces enclosing the column area.
2. Shear Walls or Ties: Steel rods or struts securing panels against lateral pressure.
3. Waler or Strongback: Horizontal member distributing load and providing support.
4. Kickers: Inclined braces maintaining vertical alignment of formwork.
5. Form Ties: Steel ties holding formwork panels together.
6. Formwork Accessories: Wedges, clamps, bolts, and nuts for assembly and adjustments.

Formwork for Slab

Formwork for slabs, also known as decking or form decking, is used to support and contain the concrete during the construction of horizontal slabs. Here are the key components and steps involved:

1. Joists or Beams: Horizontal supports for the formwork system.
2. Stringers: Parallel members aligning and supporting formwork panels.
3. Formwork Panels: Flat surfaces creating the slab structure.
4. Props or Shoring: Vertical supports carrying the formwork and concrete load.
5. Formwork Accessories: Clamps, wedges, bolts, and nuts for assembly.
6. Reinforcement: Steel bars or mesh enhancing slab strength.

Construction of Concrete Formwork

The construction of concrete formwork involves several steps to create temporary structures that shape and support the poured concrete until it sets and gains sufficient strength. Here is an overview of the process:

1. Design and Planning: Determine formwork dimensions and layout based on drawings.
2. Material Selection: Choose suitable formwork material.
3. Preparation of Formwork Components: Cut and treat panels, fabricate additional components.
4. Foundation Preparation: Level and stabilize the ground.
5. Assembly of Formwork: Erect and connect formwork components securely.
6. Reinforcement Placement: Install steel reinforcement within the formwork.
7. Alignment and Leveling: Ensure formwork is aligned and level.
8. Bracing and Support: Provide adequate support and bracing for formwork.
9. Formwork Inspection: Check for defects and rectify any issues.
10. Concrete Pouring: Carefully pour concrete into the formwork.
11. Concrete Curing: Allow concrete to cure under proper conditions.
12. Formwork Removal: Remove formwork systematically, taking care not to damage the concrete.