RAB anchors

What is a RAB anchor?

RAB stands for Repair of composite concrete slab floor anchors. Dit speciaal ontwikkelde ankersysteem is ontworpen om constructieve problemen in breedplaatvloeren veilig en duurzaam te herstellen. De ontwikkeling van het RAB-anker kwam in een stroomversnelling na het instorten van de parkeergarage bij Eindhoven Airport tijdens de bouwfase. Uit onderzoek bleek dat een ontwerpfout in de toepassing van breedplaatvloeren de oorzaak was van het incident.

Because wide slab floors have been widely used in the Netherlands, many buildings had to be structurally recalculated according to stricter safety standards. When the load on a floor exceeds a critical limit, immediate safety measures are necessary until the floor structure has been permanently reinforced.

A prestressed concrete slab floor, also known as a ribbed slab floor or hollow-core slab floor, is a type of floor construction used in buildings.

A wide slab floor is a commonly used prefabricated floor system solution in residential construction, commercial buildings, and car parks. The floor consists of prefabricated concrete elements in which the bottom reinforcement and main reinforcement have already been installed at the factory.

So-called lattice girders project upwards from these elements. These hold hollow plastic balls in place, which serve as weight-reducing elements. The thicker the floor, the greater the diameter of these balls.

Advantages of precast floor slabs

Ribbed slabs offer several advantages:

  • Large spans possible
  • Fewer supporting columns needed
  • Fast construction time
  • Weight of the structure itself
  • Suitable for both residential and commercial buildings

The floor elements are connected to each other with special coupling rods. These rods ensure that tensile forces in the transverse direction are safely transferred between the different prefabricated elements.

Once installations such as pipes, electricity and climate control have been fitted, a concrete screed is poured over the floor. The floor must remain fully supported until this concrete layer has fully hardened.

What went wrong with composite floors?

Switch to self-compacting concrete

During the production process, precast flooring was adapted by using self-compacting concrete. This meant the concrete no longer needed to be compacted using vibratory needles, which made the production process faster and more efficient.

Additionally, it was decided to omit the outer vertical reinforcement at the edges of the floors. This reinforcement regularly caused problems during the transport and lifting of the precast elements.

Origin of the constructive problem

These changes created a dangerous situation in practice:

  1. The coupling rods ended up on a very smooth layer of self-compacting concrete.
  2. Due to the absence of the outer lattice girders, there was insufficient connection between the precast floor and the subsequently poured topping layer.

This resulted in insufficient adhesion between the two concrete layers. The starter bars could no longer effectively transfer tensile forces, meaning the cast-in-situ concrete layer could detach from the precast base layer under load.

This phenomenon is also called delamination or the “peeling off” of the print layer.

The solution: the RAB anchor system

Using the RAB anchor system, the structural integrity of the floor can be restored without a complete replacement of the floor structure.

Inspection and scanning

Before the repair begins, a concrete scanner will be used to identify the exact position of:

  • existing reinforcement
  • Coupling rods
  • plastic balls

accurately mapped out.

This allows the anchors to be placed with extreme precision without damaging the existing structure.

How does a RAB anchor work?

The RAB anchor is placed to the left and right of critical floor seams, directly next to the existing reinforcing bars. This reconnects the poured topping layer constructively with the precast floor.

The required quantity of anchors and their dimensions depend on:

  • Floor thickness
  • Tax
  • Structural requirements
  • floor span

Benefits of RAB anchors

Safe refurbishment of existing structures

RAB anchors make it possible to safely strengthen existing composite slabs without large-scale demolition work.

Minimal disruption

As the repair work is largely carried out from below, buildings often remain partially occupied during the works.

Constructively demonstrable reinforcement

The pre-tensioning and testing of each individual anchor provides directly verifiable quality assurance.

Sustainable solution

The system ensures a durable structural connection between prefabricated floor and screed.

Applications of RAB anchors

RAB anchors are used in applications including:

  • Car parks
  • apartment blocks
  • Office buildings
  • hospitals
  • Schools
  • Utilities construction
  • distribution centres

In particular, buildings constructed between approximately 1995 and 2017 could be at risk of structural problems with flat slab floors.

Why constructive scrutiny is essential

Following nationwide investigations into composite slabs, it has become clear that structural safety should never be underestimated. Regular inspection and timely reinforcement are essential to prevent risks for users and buildings.

The RAB anchor system offers a reliable and technically sound solution for the repair and reinforcement of composite slabs.