Look out of the window as your train passes through a tunnel and what do you see? “Not a lot,” could be the answer, but if your window is close to the tunnel wall and the light shines out from the carriage as it does in the London Underground, you’ll see lines and lines of cables hanging from the wall, signalling control cables, data communications cables, maybe even power cables – all suspended just outside your window, appearing to move up and down in space as the train goes past.

Of course, they aren’t just hanging there. They are fastened to the walls of the tunnel by a variety of cable brackets and hangers, some may even be lying in perforated metal troughs or in cable containment.

Designing for applications

Those brackets have been specifically designed to do the job. Their shape, strength, and even the coating on them, all vary with what they are being asked to do. Every tunnel can be unique in its requirements and as such the metal framing support and cable management needs to be flexible enough to cope with these needs.

It is important that, at the engineering stage when considering a suitable metal framing and cable management solution, some key factors are taken into account. These include environmental life cycle of the products, load carrying capacity of the cable management and the support framing, flexibility/breadth of range and special requirements.

Selecting the right material finish to suit the environmental needs dictates the life expectancy of the product solution. Galvanizing is the most widely used form of corrosion resistance and is chosen because it offers a proven and cost effective solution for longevity of resistance to atmospheric corrosion. By increasing the thickness of the zinc coating, the life expectancy of the product against corrosion can be extended. However, galvanising is not the only solution and other specialised finishes may be suitable or even an improvement. Understanding this can be beneficial in reducing costs of a project.

Deciding how to split the runs for the cables and facilities that will run through the tunnel will ultimately decide the loading requirements for support framing. Ensuring the support framing loading capabilities are met can be tricky, but by ensuring the range has full BS standard test certificates brings security to the selection.

Traditional standard straight framing has been used but, with the curved walls of a tunnel, there has always been some compromise having to be made. By using a curved support to match the tunnel radius and adjustable brackets, maximum support and horizontal accuracy can be maintained where needed when it comes to carrying the facilities and cabling.

Nearly a century

Unistrut® began developing and manufacturing cable support products during the 1920s with the original Unistrut metal framing system. Over the years, the company has added an extensive cable management range to its portfolio including cable ladders, cable trays, cable baskets and steel trunking, all available in a variety of finishes to suit different applications.

“We work closely with the clients’ project team, which provides them huge benefits in delivering their project on time and within budget. This partnership approach ensures that we optimise all aspects of the system design and means that we work together with the client to drive costs out of the project”, says Tony Kinsella, EMEA (Europe, Middle East and Africa) sales director. “The best engineered solution at the right cost is our aim when supporting our customers. Our metal framing loading software and published slip-loadings are just a couple of ways that we support our customers, and our engineers would be glad to visit and demonstrate best practice.”

It is often the case that an off-the-shelf solution is unable to answer all of a project’s needs and requirements – especially when there are specific location, timing, or environmental issues to consider. In these situations, a bespoke or tailored solution can offer the flexibility and cost effectiveness needed to successfully deliver the project. Unistrut’s ability to assess, design, build and provide ongoing project lifetime support for its systems has proven to be invaluable on global major projects.

As Unistrut celebrates its 90th anniversary, the company prides itself as much today on the quality of its products as it did in the 1920s.

Written by Paul Pryor is EMEA Marketing Director for Atkore International