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The Girder-Slab System

The Girder-slab systems are made with double T steel profiles and brick elements. Discover their characteristics and how to consolidate them

Slabs are technical elements that divide the building’s floors horizontally and support the loads placed on them. They can be made with different materials and construction solutions.

In this article, we will focus on composite slabs made of girders and blocks. This technological solution has been a fundamental step in the evolution of floor structures over time. We will explore the main characteristics of these elements and provide a clear overview of the related consolidation techniques.

When it comes to designing and verifying slabs (as with any other structural element), it is always advisable to rely on specialized tools that can simplify the structural analysis process. In this regard, we recommend you to try a structural calculation software based on BIM technology with an integrated FEM solver. With the support of this tool, you can model your structures using intelligent parametric objects and perform advanced analyses, both static and dynamic, to quickly and reliably assess the structural behavior of your buildings.

What is a Girder-slab system?

Girder-slab flooring systems represent a particular construction technique used for building floors. This technique can be considered as the evolution of traditional wooden floors, which became prominent after the introduction of steel as a building material.

This type of structure essentially consists of two elements:

  • girders: these are structural steel elements, usually made with double T profiles. Girders serve as the main support for the floor and are placed parallel to each other at regular intervals. Their double T shape provides the necessary strength to support the loads applied to the structure;
  • blocks: these are support elements placed between the beams. Usually made of brick, blocks are positioned at the lower flange of the double T profile. These elements are arranged to evenly cover the distance between the beams, forming the actual floor surface.

The floor is completed with a concrete pour that is poured over the blocks. This pour, often reinforced with welded mesh, serves to create a solid connection between the girders and blocks, forming a monolithic floor. This structure is designed to evenly distribute the loads on the floor surface, ensuring the stability and structural strength not only of the floor but also of the entire building.

Types of girder-slab systems

Girder-slab floors can be constructed in different variants, as illustrated below:

  • floor with block resting on the lower flange of the profile: this is the basic variant, where the brick blocks are placed directly on the lower flange of the steel beams, covering the distance between them. The structure is completed with a concrete pour reinforced with welded mesh. This type is certainly the simplest to construct but presents some disadvantages related to the excessive weight of the structure and the unevenness of the intrados caused by the alternation between iron and brick;
  • floor with block resting on a cover iron: it follows the same logic as the previous variant. However, it involves the introduction of an additional brick element, known as a cover iron, which covers the lower flange of the beam, providing support for the block. This configuration is designed to overcome the issues arising from the material unevenness at the intrados;
  • floor with block resting on the upper flange of the profile: in this variant, the brick blocks are placed on the upper flange of the steel beams, creating an air gap that lightens the entire structure. The floor is completed with a concrete pour over the blocks and the use of elements fixed below the lower flange of the beams, which serve to close the void between them and create a uniform surface at the intrados;
  • floor with block and small block: this represents the most complete and complex variant. In this configuration, the cover iron takes a more articulated form that allows covering the lower flange of the beam and providing support for two elements, namely a small brick block placed at the lower flange of the beam and a block glued on top of the small block with an air gap in between. This solution overcomes both the issues related to the weight of the structure and those due to material unevenness. The floor is completed with a concrete pour poured over the blocks up to the upper flange of the beams.
Types of beam and block floors

Types of beam and block floors

What are the main characteristics of a girder-slab system?

Composite floors made with beams and blocks have several advantages and ease of execution that have made them a particularly popular choice in cases where it was necessary to replace an existing wooden floor, especially in older masonry buildings.

Below are the main characteristics that have widely spread these structures:

  • high load-bearing capacity: the use of steel beams as load-bearing elements gives the structural system a considerable load-bearing capacity. Beams are designed to withstand significantly higher loads than wooden floors. This feature allows the construction of robust and reliable structures, thanks to the intrinsic strength of steel that can withstand high stresses;
  • lightweight: in some variants, the use of small blocks or lightweight solutions helps reduce the overall weight of the structure without compromising its strength;
  • durability over time: steel and brick, being resistant and durable materials, are not subject to decomposition, rot, or insect attacks like wood. Consequently, the beam and block floor offer greater durability over time and require less maintenance and repairs compared to wooden floors;
  • fire resistance: the components of the beam and block floor are non-combustible materials. This means that the floor offers better protection against fires and flame spread, significantly contributing to the safety of buildings;
  • design flexibility: the versatile nature of composite floors allows for a wide range of design configurations. This flexibility allows architects and designers to adapt the structure to the specific project requirements and contributes to achieving highly effective aesthetic and functional solutions;
  • ease of installation: the use of steel beams and brick blocks simplifies the floor installation process. These elements are manufactured in factories and transported to the construction site, reducing construction times and costs. Furthermore, their installation is straightforward, allowing for quick and efficient installation;
  • cost-effectiveness: the combination of materials such as steel and brick can be a more economical choice compared to other solutions and helps contain construction costs.

Consolidation techniques for girder-slab floors and load analysis

Despite the multiple advantages, beam and block floors also have some defects, due to the excessive deformability of steel profiles and the vulnerability of brick elements, especially when the completion concrete pour reinforced with welded mesh was omitted. Additionally, these floors were designed in the past for modest loads. This is why it is often necessary to undertake structural consolidation interventions.

The most effective actions to restore or enhance the strength of a beam and block floor include:

  • overlaying a concrete slab: this technique involves creating a concrete slab on the existing floor surface. The slab should have a thickness of at least 5 cm and must be reinforced with welded mesh. The slab is connected to the load-bearing steel beams using connectors. This method allows adapting the floor to current construction needs and creates a composite structure that leverages the positive characteristics of both steel and concrete, increasing the overall strength and stiffness of the floor;
  • addition of support beams: in case of weak or undersized floors, it may be necessary to add support beams to increase the load-bearing capacity of the floor. These beams are placed parallel or perpendicular to the existing beams and distribute the load more evenly, reducing floor deformation;
  • repair or replacement of damaged elements: if specific parts of the floor, such as beams or blocks, are damaged, it is necessary to proceed with the repair or replacement of these elements. This ensures the structural integrity of the floor and prevents further deterioration;
  • application of fiber-reinforced materials: the use of fiber-reinforced materials, such as glass or carbon fiber meshes, is an effective and innovative option to reinforce the floor. These materials are applied to the floor surface using special resins or mortars, providing additional strength and improving structural performance.

Before proceeding with any intervention, it is important to verify the behavior of the floor under the action of loads through structural analysis.

You can simplify and make the entire process more reliable by using a structural calculation software.

To delve into defining load analyses of elements like beam and block floors, I recommend watching the video below.

With this tool, you have an advanced system that allows you to model your structures in a BIM environment using intelligent parametric objects. Each element will have a unique information database that will allow you to identify its physical, geometric, and dimensional characteristics uniquely.

Thanks to the power of the integrated FEM solver, you can perform advanced analyses in extremely rapid times with highly reliable results, which you can also visualize graphically. You can discover these and other features by trying this tool for free for thirty days.

 

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Edilus