Choosing the right anchor to fasten channel to concrete

Channel support systems are often fixed to walls or ceilings to provide solid support for other building services. Whether you are using Unistrut fixings or generic strut work, you probably don’t need to be told that, when anchoring structures to concrete walls or ceilings it is important to use the right sort of fixing for the job. When you fix something like Unistrut channels that will be used to carry ducting, plumbing, electrical cabling, or data wiring, you want the structure to stay fixed. You also want to get the job done quickly and economically with the minimum of fuss and waste. So, what are the options and the pros and cons of each alternative method of fixing? There are many options for providing a solid fixing for a channel to concrete or other substrates including:

Expanding anchors

One of the cheapest options in terms of unit cost, expanding anchors are inserted into a pre-drilled hole of the correct diameter. When the bolt or stud is screwed in and tightened up, the anchor expands against the sides of the hole making a solid fixing.

Advantage – relatively cheap and simple.

Disadvantage – expansion requires sound concrete, and the fixing cannot be repositioned.

• Wedge anchors

Wedge anchors are cheap and simple to use and can be combined with a bolt or stud to provide effective fixing. As the stud is tightened it forces the wedge to open up into the hole in the same way as a rawlplug.

• Through bolt anchors

A high-performance one-piece expansion bolt ideal for heavy duty through anchors into concrete and brick. On tightening, the bolt expands the collar at the end to provide the fixing.

• Shield anchors

Shield anchors can be used with any bolt, stud, or other threaded fixings of the right size. The tightening of the bolt pulls a wedge which forces the surrounding shield to open up into the hole.  

• Sleeve anchors

A through fixing with an elongated expansion sleeve for use with brick as well as concrete.

All these anchors are available in a range of lengths and thread sizes.

Resin anchors

For certain applications, a resin anchor system is needed. Although more expensive, this system is ideal when an exceptionally secure fixing is required, such as where the fixings are overhead or in any situation where a failure would be catastrophic. The resin capsule is inserted into a predrilled hole and the thread is then screwed into it. This gives a very high strength fixing which benefits from not expanding into the surrounding material meaning it can be used in wet or cracked materials and close to edges.

Advantage – very strong reliable anchor, doesn’t expand.

Disadvantage – high cost.

Concrete screws

While rather more expensive to buy than expanding anchors, concrete screws offer several advantages over traditional concrete fixings. Since they are self-tapping with only a small pilot hole required, they are a lot faster to install, and there is considerably less dust produced. They also require less skill to use correctly and can be used close together or close to edges since they do not significantly expand in the material. Another advantage to concrete screws is that, unlike resin or expansion fixings, they can be repositioned. In a great many installations, the additional cost of the product will be more than offset by cost savings for time and manpower.  

Advantage – easy and quick to install and reposition.

Disadvantage – high cost.