Site icon Building & Decor

Mounting through bolts: Getting it right

Mounting through bolts

Through bolts are frequently used as mechanical anchoring solutions for heavy loads in cracked or non-cracked concrete. 

Market leader in engineered fasteners and joining technology, EJOT, advises on the special features and functionality of through bolts, and offers valuable tips on how to avoid installation faults. 

What is a through bolt? 

A through bolt is a torque-controlled expansion anchor (frictionally engaged) for fastening metal and wooden attachments (medium-heavy to heavy loads) to concrete. It meets high requirements for loadbearing capacity and safety. 

Through bolts are used for fastening heavy and safety-relevant attachments in both indoor and outdoor areas. These include: 

For outdoor areas, through bolts are made of A4 stainless steel or HCR 1.4529 stainless steel, which is well suited for highly corrosive environments. 

How do through bolts work? 

Through bolts work by driving a steel bolt into the base material. The correct setting depth can be easily determined by the black marking on the anchor. When installed, this marking must be flush with the concrete surface. 

When the nut is tightened, a metal shield expands, which in turn clamps the bolt into the substrate. Depending on the respective assessment, through bolts are suitable for anchoring in cracked and non-cracked concrete. 

Caution on edges 

Due to the expansion forces, the through bolt as a fastening element has limits in some applications. This is mainly when the fixing points are close to the edge of concrete surfaces. 

If the concrete does not have enough mass to absorb the expansion forces, the result may be splitting of the substrate material and in the end even complete failure of the fixing point. 

In these cases it is better to use a concrete screw, undercut anchor or chemical anchor. 

Installation mistakes 

There are three common mistakes when installing through bolts. 

Fastening point too close to the edge 

This example shows a metal handrail that has been fastened to concrete steps with through bolts. The fastening points are at the outer edge of the steps. 

The occurring expansion forces have damaged the surface of the concrete. In some parts the entire concrete corner has split. 

The fastening point is too close to the outer edge of the step (top). The corner of the step is broken – this is not going to bear loads (bottom).

Angled through bolts 

This installer knew that edges are critical and tried to prevent splitting by installing the through bolts at an angle. This second installation error is the reason why the through bolt could not be mounted flush with the attachment. 

The through bolt was installed at an angle and could not be mounted flush with the attachment.

Selection of the wrong attachment point 

Out of four possible attachment points, only two were chosen – the two least favourable ones, sitting directly on the edge. 

Here the expansion forces of the through bolts create a risk that the edge areas of the concrete will split, and the fastening will completely or at least partially lose its loadbearing capacity. 

The fastening points were chosen poorly, too close to the edge area.

Not cleaning the drill hole 

All concrete anchor drill holes must be cleaned of dust and debris before anchor installation, using a suitable hole-brush and blow-out pump (or compressed air). Debris prevents the anchor from being installed to its correct depth, and dust reduces the anchor’s pull-out capacity. 

Avoiding damages 

When using through bolts in concrete, the minimum edge distances must be observed and strictly adhered to, to ensure the comprehensive loadbearing capacity of the fastening. Additionally, drill holes must always be made perpendicularly and cleaned as instructed. 

To avoid errors use EJOT’s free to use anchorage design software, Anchorfix. It can be downloaded from www.ejot.com. 

Spacing, edge distance and performance information can also be obtained from the anchor’s European technical Assessment (ETA) document, which can also be downloaded from www.ejot.com. 

Alternative Anchorages 

If it is not possible to observe the minimum distances for structural reasons, there are three alternatives to use which have better edge distance tolerance: 

  1. Concrete screws such as EJOT JC2 Plus 
  2. Chemical anchors such as EJOT VSF+ Seismic 
  3. Undercut anchors such as EJOT Liebig Superplus 

 

Avoid installation faults when mounting through bolts with these practical tips from industry experts.  

 

For more information, contact EJOT: 

Tel: +27 21 830 5420 

Email: infosa@ejot.co.za 

Website: https://www.ejot.com/ 

Exit mobile version