Types of Formwork for Concrete Structures

13 May.,2024

 

Types of Formwork for Concrete Structures

Concrete is one of the most widely used construction materials, thanks to its exceptional properties. However, to create building elements with concrete, it must be poured into a specially designed mold. This is known as formwork or shuttering.

If you are looking for more details, kindly visit our website.

Formwork can use temporary or permanent molds, which hold the poured concrete in shape until it hardens and achieves enough strength to support itself. Formwork can be classified in many ways:

  • Type of material used
  • By the concrete element supported
  • Removable or permanent

Formwork has a fundamental role in concrete construction. It must have enough strength to bear all the loads present during casting operations, and must then hold its shape while concrete hardens.

Deploy best practices in construction administration for your project.

Which Are the Requirements for Good Formwork?

Although there are many formwork materials, the following are general performance features to meet the needs of concrete construction:

  1. Capable of withstanding dead and live loads.
  2. Retaining its shape with adequate props and braces.
  3. Joints must be leak-proof.
  4. If formwork is removable, the process must not damage the concrete.
  5. Reusable material.
  6. As lightweight as possible.
  7. The formwork material should not warp or distort.

When selecting formwork it is important to consider the type of concrete and the pouring temperature, since both affect the pressure exerted. Also, formwork must be capable of resisting the loads of wet and dry concrete.

Formwork requires structures such as poles and stabilisers to avoid movement during construction procedures, and these are called falsework. To ensure high quality when working with concrete, a qualified workforce and adequate supervision are necessary.

The following sections provide an overview of some common formwork materials.

Timber Formwork

Timber formwork was one the first types used in construction industry. It is assembled on site and is the most flexible type, bringing the following advantages:

  • Easy to produce and remove
  • Lightweight, especially when compared with metallic formwork
  • Workable, allowing any shape, size and height
  • Economical in small projects
  • Allows the use of local timber

However, before using timber its condition must be checked carefully, making sure it is free of termites. Timber formwork also has two limitations that must be considered: it has a short life span and is time consuming in large projects. In general, timber formwork is recommended when labor costs are low, or when complex concrete sections require flexible formwork.

Plywood Formwork

Plywood is often used used along with timber. It is a manufactured wooden material, which is available in different sizes and thicknesses. In formwork applications, it is mainly used for sheathing, decking and form linings.

Plywood formwork has similar properties as timber formwork, including strength, durability and being lightweight.

Metallic Formwork: Steel and Aluminum

Steel formwork and steel hardware is becoming more popular due to its long service life and multiple reuses. Although it is costly, steel formwork is useful for multiple projects, and it is a viable option when many opportunities for reuse are expected.

The following are some of the main features of steel formwork:

  • Strong and durable, with a long lifespan
  • Creates a smooth finish on concrete surfaces
  • Waterproof
  • Reduces honeycombing effect in concrete
  • Easily installed and dismantled
  • Suitable for curved structures

Aluminum formwork is very similar to steel formwork. The main difference is that aluminum has a lower density than steel, which makes formwork lighter. Aluminum also has a lower strength than steel, and this must be considered before using it.

Plastic Formwork

This type of formwork is assembled from interlocking panels or modular systems, made of lightweight and robust plastic. Plastic formwork works best in small projects consisting on repetitive tasks, such as low-cost housing estates.

Plastic formwork is light and can be cleaned with water, while being suitable for large sections and multiple reuses. Its main drawback is having less flexibility than timber, since many components are prefabricated.

Fabric Formwork

Fabric formwork is also known as flexible formwork. This system uses lightweight and high-strength sheets of fabric, designed to adjust to the fluidity of concrete and create interesting architectural forms.

This formwork type uses less concrete than rigid systems, which yields savings. It is an emerging technology in the shuttering industry, especially suited for constructions of irregular and complex shapes.

Stay-In-Place Formwork

This formwork is designed to remain fixed after the concrete has set, acting as axial and shear reinforcement. This formwork is made on-site from prefabricated and fibre-reinforced plastic forms. It is mainly used in piers and columns, and also provides resistance against corrosion and other types of environmental damage.

Another type of stay in place formwork is called coffor, which can be used in any type of building:

  • It is composed of two filtering grids, reinforced by stiffeners and linked with articulated connectors.
  • Thanks to its construction, it can be easily transported from a factory to the point of use.

Tunnel Formwork

Tunnel formwork is a common construction method used in residential apartments & hotels which involves producing repetitive structural elements for buildings with the same layouts. It employs a steel formwork system that is built on the construction site to pour concrete walls and slabs in a continuous cycle. This strategy is especially effective for tasks that require quick construction and consistent design.

Tunnel formwork is extensively used in high-rise construction projects when speed and efficiency are crucial. The advantages are faster construction, high quality control, and less labor cost. The approach allows the creation of long-lasting structures fast and efficiently, making it one of the popular choices in the infrastructure industry.

Permanent Insulated Formwork

This is one of the most advanced formwork systems, offering permanent insulation. It may also include thermal, acoustic, fire-resistance and rodent-resistance properties. Insulating concrete forms (ICF) are the most common type of permanent insulated formwork, where concrete structures are insulated with polystyrene boards that stay in place after concrete has cured.

Permanent insulated formwork offers energy efficiency and sustainability, contributing to a lower environmental impact from the building sector.

Classifying Formwork Based on Structural Components

In addition to being classified by material, formwork can also be classified according to the building elements supported:

  • Wall formwork
  • Beam formwork
  • Foundation formwork
  • Column formwork

All formwork types are designed according to the structure they support, and the corresponding construction plans specify the materials and required thickness. It is important to note that formwork construction takes time, and it can represent between 20 and 25% of structural costs. To mitigate the cost of formwork, consider the following recommendations:

  • Building plans should reuse building elements and geometries as much as possible to allow formwork reusing.
  • When working with timber formwork, it should be cut into pieces that are large enough to be reused.

Concrete structures vary in design and purpose. Like in most project decisions, no option is better than the rest for all applications; the most suitable formwork for your project varies depending on building design.

Nearby EngineersNew York Engineers has a MEP design track record of 1,000+ projects. Contact us via email (info@ny-engineers.com) or phone (786) 788-0295212-575-5300, and make sure your building systems meet codes.

 

Types of Formwork (Shuttering) for Concrete Construction ...

🕑 Reading time: 1 minute

Zolo Product Page

Formwork (shuttering) in concrete construction is used as a mold for a structure in which fresh concrete is poured only to harden subsequently. Types of concrete formwork construction depends 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.

The construction of formwork takes time and involves expenditure up to 20 to 25% of the cost of the structure or even more. The design of these temporary structures are made to 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 are called stationary forms.

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

Requirements of Good Formwork

  1. It should be strong enough to withstand all types of dead and live loads.
  2. It should be rigidly constructed and efficiently propped and braced both horizontally and vertically, to retain its shape.
  3. The joints in the formwork should be tight against leakage of cement grout.
  4. Construction of formwork should permit removal of various parts in desired sequences without damage to the concrete.
  5. The material of the formwork should be cheap, readily available, and should be suitable for reuse.
  6. The formwork should be set accurately to the desired line, and levels should have a plane surface.
  7. It should be as light as possible.
  8. The material of the formwork should not warp or get distorted when exposed to the elements.
  9. It should rest on a firm base.

Economy in Formwork

The following points are to be kept in view to effect economy in the cost of formwork:

  1. The plan of the building should imply a minimum number of variations in the size of rooms, floor area, etc. to permit reuse of the formwork repeatedly.
  2. Design should be perfect to use slender sections only in the most economical way.
  3. Minimum sawing and cutting of wooden pieces should be made to enable reuse of the material many times. The quantity of surface finish depends on the quality of the formwork.

Formwork can be made out of timber, plywood, steel, precast concrete, or fiberglass used separately or in combination. Steel forms are used in a situation where large numbers of re-use of the same forms are necessary. For small works, timber formwork proves useful. Fiberglass made of precast concrete and aluminium are used in cast-in-situ construction such as slabs or members involving curved surfaces.

Types of Formwork (Shuttering)

1. Timber Formwork

Timber for formwork should satisfy the following requirement:

It should be:

  1. Well-seasoned
  2. Light in weight
  3. Easily workable with nails without splitting
  4. Free from loose knots

Timber used for shuttering for exposed concrete work should have smooth and even surface on all faces which come in contact with concrete.

Table 1: Normal sizes of members for timber formwork

Sheeting for slabs, beam, column side, and beam bottom25 mm to 40 mm thickJoints, ledges50 x 70 mm to 50 x 150 mmPosts75 x 100mm to 100 x 100 mm

2. Plywood Formwork

Resin-bonded plywood sheets are attached to timber frames to make up panels of the required sizes. The cost of plywood formwork compares favorably with that of timber shuttering, and it may even prove cheaper in some instances given the following considerations:

  1. It is possible to have a smooth finish in which case on cost in surface finishing is there.
  2. By the use of large-size panels, it is possible to affect saving in the labor cost of fixing and dismantling.
  3. The number of reuses are more as compared with timber shuttering. For estimation purposes, the number of reuses can be taken as 20 to 25.

3. Steel Formwork

This consists of panels fabricated out of thin steel plates stiffened along the edges by small steel angles. The panel units can be held together through the use of suitable clamps or bolts and nuts.

The panels can be fabricated in large numbers in any desired modular shape or size. Steel forms are largely used in large projects or in a situation where large number reuses of the shuttering is possible. This type of shutter is considered most suitable for circular or curved structures.

Comparison between Steel and Timber Formwork

  1. Steel forms are stronger, durable, and have a longer life than timber formwork and their reuses are more in number.
  2. Steel forms can be installed and dismantled with greater ease and speed.
  3. The quality of exposed concrete surface by using steel forms is good and such surfaces need no further treatment.
  4. Steel formwork does not absorb moisture from concrete.
  5. Steel formwork does not shrink or warp.

Construction of Concrete Formwork

This normally involves the following operations:

  1. Propping and centering
  2. Shuttering
  3. Provision of camber
  4. Cleaning and surface treatment

Order and Method of Formwork Removal

The sequence of orders and method of removal of formwork are as follows:

  1. Shuttering forming the vertical faces of walls, beams, and column sides should be removed first as they bear no load but only retain the concrete.
  2. Shuttering forming soffit of slabs should be removed next.
  3. Shuttering forming soffit of beams, girders, or other heavily loaded shuttering should be removed in the end.

Rapid hardening cement, warm weather and light loading conditions allow early removal of formwork.

The formwork should under no circumstances be allowed to be removed until all the concrete reaches a strength of at least twice the stresses to which the concrete may be subjected at the time of removal of formwork.

All formworks should be eased gradually and carefully in order to prevent the load from being suddenly transferred to concrete.

Figure 1 to 6 shows formwork for different types of members in civil engineering construction.

Figure 1(a): Details of Timber Formwork for RCC Beam and Slab Floor Figure 1(b): Details at Section (A) Shown in Above FigureFigure 2(a): ElevationFigure 2(b): Details of Timber Formwork for Circular RCC ColumnFigure 3(a): 150 3D ViewFigure 3(b): Details of Timber Formwork for Square or Rectangular RCC ColumnFigure 4: Sectional Plan Showing Details of Timber Formwork for an Octagonal ColumnFigure 5: Details of Formwork for StairFigure 6: Timber Formwork for RCC Wall

Table 2: Period of Removal of Formwork

S. No.Description of structural memberTime Period1Walls, columns and vertical sides of beams1 to 2 days2Slabs (props left under)3 days3Beam soffits (props left under)7 days4Removal of props to slabs(a) For slabs spanning upto 4.5 m7 days(b) For slabs spanning over 4.5 m14 days5Removal of props to beams and arches(a) Spanning upto 6 m14 days(b) spanning over 6 m21 days

FAQs on types of formworks and their properties

?What are the types of formworks?

1. Timber formwork
2. Plywood formwork
3. Steel formwork

?What is formwork in building constructions?

Formwork is used to describe the process of building temporary molds in to which fresh concrete is poured to construct designated structural concrete elements and achieve its shape.

?What are the requirements of formworks?


1. Adequately strong to withstand all types of loads.
2. Rigid enough to retain its shape.
3. Joints in the formwork tight against leakage of cement grout.
4. Formwork construction should permit the removal of various parts in desired sequences without damage to the concrete.
5. The formwork material should be cheap, readily available, and reusable.
6. The formwork should be set accurately to the desired line, and levels should have a plane surface.
7. It should be as light as possible.
8. It should rest on a firm base.

?How much does a formwork cost in comparison to the total cost of the structure?

The construction of formwork takes time and involves expenditure up to 20 to 25% of the cost of the structure or even more.

?What are the requirements of timber formwork?

1. Well-seasoned
2. Light in weight
3. Easily workable with nails without splitting
4. Free from loose knots

Read More:

Plastic Formworks for Concrete – Applications and Advantages in Construction

Wooden Concrete Formwork Design Criteria with Calculation Formulas

Concrete Formwork Loads and Pressure Calculations

Formwork Removal Time & Specifications

Measurement of Formworks

Formwork (Shuttering) for Different Structural Members -Beams, Slabs etc

Formwork Safe Practices Checklist

For more information, please visit concrete slab formwork systems.