#Mechanical anchor

Fixing with steel anchors

6 min

Mechanical fixings have been in use since the beginning of the 20th century, and they still remain the most popular type of heavy-duty fixings, especially when used in concrete.

Some of their numerous advantages include high load capacity, simplicity of installation, and – in the case of screw-in anchors – the possibility of fixing directly next to edges and adjacent anchors.

This article will introduce you to the different types of mechanical fixings and the ways to install them.

What are steel anchors?

Also referred to as mechanical anchors, they are – to put it simple – metal connecting pieces intended for single- and multi-point structural and non-structural fixing. They are made entirely of steel.

What is a throughbolt and how to use it?

This is one of the most common types of steel anchors. The hole diameter matches that of the anchor.
There are two setting depths defined for throughbolts: standard and reduced, making it possible to freely adjust the anchoring depth to the fixture thickness.

kotwa opaskowa jak działa
Zinc-plated throughbolt.

When preparing for an installation job using a throughbolt, you need to prepare the following:

  • drill bit of the right size,
  • hand pump to remove drillings from the hole,
  • hammer to drive the anchor in,
  • torque wrench to tighten the anchor to the correct torque.

Must-know fact

Throughbolts and screw-in anchors can be used for straight-through fixing, which makes work much easier and faster, especially when handling heavy objects. With these two types of anchors at hand, you can quit pre-installing the connecting piece.

What are screw-in anchors and how to use them?

Also known as concrete screws or bolts, their operating principle is similar to that of wood screws. The anchor’s shape and the fixing method employed are the reasons why anchoring takes place along the entire length of the hole, making the most of friction rather than expansion forces. This makes concrete screws suitable for fixing in close proximity of edges and nearby anchors, which proves particularly important when installing elements such as railings or balustrades.

kotwa stalowa wkręcana w beton działanie
Steel anchor for concrete applications, or simply concrete screw.

The screw-in anchors from Rawlplug come in as many as seven head variants, which significantly extends the range of their potential applications. Screw-in anchors also offer the possibility of fixture adjusting, e.g. when it has originally been installed crooked. According to the approval, we can loosen the anchor by up to 10 mm, correct the fastening, and tighten the screw into the concrete again without losing its load bearing capacity. The approval allows this to be done twice.

This is what you need for fixing with screw-in anchors:

  • drill bit of the same size as the anchor,
  • hand pump to clean the hole,
  • impact wrench to tighten the anchor.

Must-know fact!

Screw-in anchors can be removed completely, which makes them suitable for temporary installation. 

Shield anchors – fixing and applications

Shield anchors were actually the first to have been patented as mechanical anchors back in 1934, only to mark the onset of the entire industry’s further development.

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Iconic RAWLBOLT shield anchor.

With the unique design, shield anchors are suitable for use even in weak substrates. Additionally, they come in several variations, making it much easier to select an anchor for a specific application. 

Thanks to the long expansion zone, you can use this type of anchor in the most demanding substrates, such as cracked concrete, but also in solid bricks, precast blocks, or hollow core slabs.

Unlike the steel anchor types discussed above (throughbolts and screw-in anchors), the shield anchor requires using a drill bit of a larger diameter than that of the fixing

Fixing with shield anchors.

  1. Drill a hole to the adequate diameter and depth.
  2. Blow out drillings using a hand pump at least four times.
  3. Remove the nut and washer, insert the anchor sleeve into the hole, and tap it with a hammer until it comes flush with the substrate.
  4. Place the nut and washer on the threaded rod and, using a torque wrench, tighten them to the required torque.

The following table details parameters conditioning the choice of the drill bit size:


Discover RAWLBOLT!

The Rawlbolt shield anchor is available in as many as six variants!

Hammer-in sleeve anchors – how do they work?

Sleeve anchors are typically used for installation of piping, ventilation, and cable tray systems. The design of this particular steel anchor allows you to use both metric bolts or threaded rods for fixing, as they can be screwed directly into the anchor. 

Fixing with sleeve anchors proceeds as follows:

  • drill a hole using a drill bit with a special stop collar which prevents drilling a hole larger than needed,
  • place the anchor inside the hole and hammer it in with a mallet,
  • use the mallet to drive the anchor all the way through to make sure that it has been set correctly in the substrate,
  • the conical section expands the anchor and sets it securely in the substrate.
jak działa kotwa tulejowa Rawlplug
SafetyPlus sleeve expansion anchor designed specifically for heavy-duty applications.

Which steel anchor to choose?

When choosing the right mechanical fixing, consider the following parameters:

  • substrate type – all mechanical anchors can be used in non-cracked and reinforced concrete, while some can also be used in cracked concrete;
  • corrosion category – depending on where the anchor is to be installed and what weather conditions it will be exposed to, choose a solution of the right corrosion resistance category;
Atmospheric corrosion (corrosivity) category as per ISO 12944-2ExteriorInterior
C1 Very low-Interior of ventilated facilities with a clean atmosphere (e.g. shop, office, hotels)
C2 LowAtmosphere contaminated to a small extent, mainly rural environmentNon-heated buildings where condensation can occur (e.g. warehouses)
C3 MediumResidential and industrial areas with moderate pollution and low salinityLight industry with damp and polluted atmosphere (food production, laundries, etc.)
C4 HighIndustrial and coastal areas; atmosphere with moderate salinityChemical plants, swimming pools, sea ships, etc.
C5-I/M Very highInshore and offshore areas with slightly aggressive or highly aggressive atmospheric conditions with high salinity and humidityBuildings and facilities with condensation and high pollution levels
  • fixture design – it is important to check whether the fixture to be installed can be installed using a specific anchor. For example, what may be required when dealing with certain loads is straight-through fixing or the use of a flat head bolt to come flush after anchoring, or even pre-installation using a threaded rod and a nut;
  • load capacity and installation parameters – the anchor’s capability to transfer a specific type of load.

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