In modern construction, formwork beams play an important load-bearing role in formwork systems used to construct cast-in-place and ribbed slabs. Their proper selection and positioning are essential not only for maintaining structural continuity but also for ensuring safety during construction work. This guide provides practical information on the specifications, applications, and principles of using formwork beams, making it useful for both designers and contractors.

The Role of Formwork Beams in a Formwork System

Formwork beams are a fundamental supporting component in slab and roof formwork systems. Their purpose is to transfer the weight of formwork panels, fresh concrete, and reinforcement to props or other intermediate supports. The proper formation of the slab and safety on site depend on the strength and positioning of these beams.

When constructing a cast-in-place concrete slab, the weight of the concrete can reach as much as 500 kg/m² for a thickness of 20 cm. At the design stage, it is therefore necessary to consider both the type and the number of formwork beams. Properly selected slab formwork beams help distribute loads evenly and reduce the risk of uncontrolled formwork deflection. This directly contributes to the slab's durability during everyday use.

Types of Formwork Beams Used in Formwork Systems

The type of supporting beams used depends on the slab structure, its span, and the anticipated loads. Common solutions include timber formwork beams, which offer good load-bearing capacity and are easy to work with. Timber formwork beams are most often manufactured as I-beams made from glued laminated timber. Their lengths range from 1.0 m to as much as 5.9 m. Their lightweight construction makes transport and installation easier, helping speed up assembly work. When properly protected against moisture, they can be reused many times, making them an economical solution for construction companies.

Positioning Roof Formwork Beams

When a design involves longer slab spans, choosing the right type of beam becomes particularly important. In such cases, beams with larger cross-sections are used, often supported by additional intermediate props. The position of each supporting element must always comply with the technical documentation and take the load distribution into account. For longer spans, timber beams may require props to be placed closer together to provide adequate structural stiffness. An error in this regard can lead to damage to the slab formwork panels during concreting.

Applications of Formwork Beams in Roof Structures

In addition to their traditional use in slabs, timber roof beams are also used in the construction of pitched and flat roofs. In roof structures, they act as load-bearing beams that support the weight of the roof covering and resist forces caused by wind gusts and snow loads. In steel-framed halls, particularly those with low-pitch roofs, roof beams form a spatial load-bearing grid that works together with steel components and prefabricated roof panels. They not only transfer loads but can also support suspended building services, such as ventilation ducts.

Preparing the Construction Site for Formwork Installation

Before formwork installation begins, the construction site must be prepared. This includes levelling the ground, providing access for cranes, and designating material storage areas. These measures are important for organising the entire process. Proper storage of components such as formwork beams, props, and panels prevents damage and makes them easier to access during construction. At the same time, work is carried out on the foundations that will support the columns of the slab support structure.

Glued Laminated Timber Beams – Strength Calculations

One important design parameter for reinforced concrete slabs is their load-bearing capacity, which directly affects the possible span between supports. As a general guideline, the imposed load on a floor slab, including people and furnishings, is assumed to be approximately 1.5 kN/m², or around 150 kg/m². The greater the planned span, the higher the load-bearing capacity of the entire system must be. This affects both the reinforcement design and the positioning of the formwork beams. For example, in single-family houses, typical slab spans do not exceed 7 metres. How do you calculate the load-bearing capacity of a timber floor? When the load-bearing capacity of structural elements, including floor beams and formwork, needs to be determined precisely, consultation with a construction specialist is essential.

Timber Floor – Load-Bearing Capacity

Correctly positioning the supporting beams and arranging them in relation to one another allows vertical loads to be transferred efficiently. Formwork systems must be secured against both horizontal and vertical movement using suitable connectors and stabilising systems. These safeguards are particularly important in adverse weather conditions, such as strong wind gusts. In addition, the structure must be designed to withstand the loads imposed by the reinforcement and the self-weight of fresh concrete.

Installing Formwork Beams – Step by Step

Correct installation of formwork beams requires compliance with the procedures specified in the technical documentation. The work begins with positioning the supporting props. Their number and spacing are determined by the length and load-bearing capacity of the beams, as well as the planned weight of the fresh concrete and reinforcement.

Once the vertical supports have been positioned, the formwork beams are laid at specified intervals, usually 50–100 cm apart. Regardless of the type of beam used, stability and level must be checked to prevent movement during subsequent stages of work. The next step is to install the formwork decking using timber boards or panels. Panels cover a larger area, which can shorten installation time and reduce the number of joints.

The Importance of Stability and Precision During Installation

Proper support of the entire system is crucial for achieving the required load-bearing performance of the slab. Every formwork component, from the props and beams to the decking, must be stable and securely positioned. In practice, this means checking vertical and horizontal deviations before concreting begins. For larger slab areas and work involving prefabricated elements, beams support not only the decking but also the handling and installation of prefabricated components. In many cases, they enable panels to be installed quickly using specialist equipment, eliminating the need for time-consuming full timber boarding.

Roof Beams in Production Halls and Large-Volume Buildings

Production halls and warehouses with large structural spans require beams with increased load-bearing capacity. These beams can support heavier loads and allow technical equipment to be installed on steel or reinforced concrete columns. Slab formwork beams in such buildings also allow open-plan spaces to be designed without the need to increase the number of supports. Proper positioning and preparation of connections can also make it possible to suspend building services, simplifying the routing of cables, ducts, and air supply systems.

Safety During Installation Work

Strict safety procedures must be followed when carrying out installation work involving formwork beams. This includes checking the technical condition of the props, verifying the stability of the system, and using safeguards to prevent structural components from moving. Environmental factors, such as wind speed and precipitation, must also be taken into account. Unexpected rainfall can weaken the grip between components or reduce the stability of the ground supporting the props. In such situations, the work schedule may need to be adjusted or additional safeguards installed for the temporary structure.

Formwork Removal and Reuse of Components

Once the concrete has set and the slab has reached the required load-bearing capacity, formwork removal can begin. The timing depends on the ambient temperature, the type of concrete mix, and the depth of the slab section. In practice, formwork is often removed after several days, but the process must not be accelerated without consulting the site manager. Dismantled timber beams can be reused provided they show no signs of damage or loss of mechanical properties. Components with structural damage, such as cracks or twisting, must be taken out of service.

How Formwork Beams Affect Slab Performance

The final quality of a slab depends not only on the concrete mix and the quality of the reinforcement but also on the correct positioning of the supporting components. Incorrect positioning of a load-bearing element can cause deformation or uneven load distribution. High-quality workmanship directly affects structural durability, reduces the need for remedial work, and enables the slab to be used safely over the long term. Correct beam spacing and positioning ensure that loads are transferred evenly, including the self-weight of the structure and the loads imposed by occupants and furnishings.

Installing Steel Structures – Can Timber Beams Be Used?

During the installation of steel structures, such as warehouses or shelters, timber beams can be used as temporary auxiliary supports. They may help stabilise smaller sections of the structure or support components before permanent connections are completed. This type of support can be useful during the initial stages of work, particularly with lightweight components where cranes are not immediately required.

For timber supports to be used safely, the position of each component must be determined precisely, and the connection must be prepared in accordance with the technical documentation. Timber roof beams may also be useful for temporarily suspending building services, such as installation ducts. However, the differences between timber and steel in terms of load-bearing capacity and stiffness must be considered, particularly when dealing with longer spans.

What Should You Consider When Working with Formwork Beams?

Working with formwork beams requires not only knowledge of installation procedures but also an assessment of the technical conditions on the construction site. Key considerations include the loads involved, the type of slab, the planned use of the components, and their storage conditions. Only proper site preparation, appropriate material selection, and checks at every stage—from installation to formwork removal—can ensure high-quality workmanship and reduce the risk of structural damage.

Where Can You Buy Reliable Formwork Beams and Formwork Components?

If you are looking for reliable solutions for slab construction or temporary structures, our formwork store offers a wide range of formwork beams, props, and other components essential for construction work. We offer components suited to a variety of loads and project types.

FAQ

1. Can you design the layout of formwork beams on site yourself?

No. The beam layout should follow the design documentation prepared by a qualified structural engineer. Modifying the arrangement independently can overload components, creating a risk of structural damage or accidents during construction.

2. How should timber formwork beams be stored between uses?

Timber formwork beams should be stored in a dry, well-ventilated place, preferably on supports that keep them off the ground. They should not be exposed to precipitation or prolonged direct sunlight. Proper storage extends their service life and reduces the risk of deformation.

3. Can formwork beams be used for concrete slabs poured directly on the ground?

No. Formwork beams are not needed for concrete slabs poured directly onto the ground. These works generally use perimeter formwork made from timber boards or panels. Beams are required for structures above ground level where the formwork needs full support from below.