Taking a new approach to light mast design

Sports lights are infrastructure that everyone sees, but few take notice of.

There are the sports lights at your local park: the 15-20m light poles that allow locals to enjoy the outdoors and get active after dark. Then there are the stadium lights: the 25-50m towers that set professional sports fields aglow.

Just as the heights of the towers differ depending on their purpose, so too does the luminosity. A local netball court might only require a tower fitted with one or two light fixtures (called luminaries), a local soccer field might need 10, and a large professional stadium might need towers with up to 88 luminaries, in order to offer crystal-clear night-time telecasts.

Typically, there is a lot of input and focus on the light that the tower delivers and the pole structure is supplied as a component of the overall lighting system. There is often very little input on the design of the pole structure that supports the lights – and that can lead to issues of safety and longevity of entire lighting system.

The dangers of traditional light mast design

In concentrating too much on the number of lumens required to light a field, councils and sports bodies don’t give the tower itself enough attention. Sometimes, specifications for the design of the pole structure are not included in the tender document. And because private companies supply and construct the towers, assurance that they will survive a 50-year design life can be lacking.

As a result, there have been a number of events where poles have collapsed.

While these events have most commonly occurred in open fields, there have been cases where poles have fallen on property and caused significant damage. The potential for injury or death is considerable, particularly if we’re talking about a packed sports stadium.

Most towers are designed to what is called the ‘ultimate limit state’. This is the worst-case scenario in terms of the conditions that the structure will be exposed to. But contrary to popular belief, a single high-wind event isn’t the reason that most towers collapse. They collapse due to fatigue – a cumulation of lower wind speeds that cause wear and tear through constant vibrations, rather than a single gust that blows a tower over. Because of this, towers usually fail at a much lower wind speed than they were designed for.

This issue isn’t helped by the fact that the Australian Standards don't offer much guidance on how to design the pole structure to account for fatigue. They provide methods for the engineer to design the structure to survive that ultimate wind speed. But that’s not how most of these poles fail.

Taking a new light mast design approach

At Arcadis we understood this problem and felt compelled to fix it. We wanted to recommend a design approach that councils and sports bodies could use when comparing pole designs from different manufacturers during procurement – one that ensured they went with a supplier that would do things the right way. We also wanted to enable local governments and private organisations to have the structures certified by an engineer once they were installed.

And so we created our Design Approach for Sports Lighting Masts document.

The certifying engineer plays the most crucial role in our new process. Having been certified to a standard based on the procedures outlined in the document, they understand that poles are most likely to fail due to fatigue, and can certify based on that fact.

Fixing this problem is more important than ever. In the fallout of COVID-19 councils want to maximise open air park usage, while stimulating the economy by hiring local contractors. Installing light towers ticks both boxes – between geotechnical, electrical, piling and concreting contractors, the construction of a light tower is a fantastic job creator. They aren’t huge projects – they generally total in the hundreds of thousands of dollars, rather than the millions – but they keep people working.

Proving the Arcadis light mast design approach in the field

Despite only recently releasing the document, it has already shown itself to be incredibly valuable to a wide range of clients. From small local parks to large sports grounds, it is giving councils, sporting bodies and other light tower customers a far better understanding of – and thus far greater control over – the towers that will light their fields.

Two large projects in New Zealand stood out to me this year – one at Hagley Oval and the other at Northland Events Centre. Both jobs required large 45m towers with close to 80 lights on them, both arenas are scheduled to host World Cup events in the next year, and both will not only experience high winds, but potential earthquake activity too. There's a lot of risk there.

As we’ve seen, if you just focus on the lighting performance, with no emphasis on the structural side of things, you’re putting people at risk. But thanks to our hard work at Arcadis, I’ve got the utmost confidence that these towers will be lighting their fields for decades to come.

Ramesh Watson

Structural Engineer Ask me a question
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