Cyclonic Wind Loading for Fixed Plant in the Pilbara
When people hear cyclone rating in the Pilbara, they picture buildings. Reasonably so. Cyclonic wind loading for fixed plant is the part that gets missed. And on a mine site it’s often the bigger exposure. A crusher, a conveyor, a run of pipe rack or a bank of solar panels has to stand up to the same category of wind as the accommodation block next to it. But none of it is a building and who can certify non-buildings? At Element Mechanical Design we assess, test and certify fixed plant for cyclonic wind loads, so the structures that keep an operation running don’t turn into the ones that fail.
The mistake is thinking only about buildings
Building codes and cyclone ratings get a lot of attention, and rightly so. But a mine site is mostly not buildings. It’s process equipment, structures and infrastructure sitting out in the open, and a Category 5 system doesn’t care whether the thing in its path has a floor plan. Wind acts on any object with a surface, and a lot of the fixed plant on a Pilbara site presents a very large surface.
When you’re considering risks in a mine site wind loading, don’t forget the following:
- Conveyor belts and crushers
- Pipe lines and water towers
- Solar panels, communication towers and lighting, both fixed and mobile lighting towers
Why the Pilbara changes the maths
The Pilbara sits in the cyclonic wind regions of AS/NZS 1170.2, Australia’s standard for wind actions. Most of the coast falls in Region C. The stretch around Port Hedland and the north west is Region D. That’s most severe wind region in the country. Design wind speeds in these regions are far higher than anywhere in the populated south. And the standard adds a further factor for the uncertainty that comes with cyclonic wind. A structure designed to a Perth wind load and shipped north is not compliant, and more to the point, not safe.
The wind doesn’t know it’s hitting a conveyor and not a house. If it has a surface, the wind loads it. On a Pilbara site the fixed plant is often the biggest sail you’ve got, and it’s the part nobody thought to check.
Daniel Berti, Head of Mechanical Design, Element Mechanical Design
What counts as fixed plant
Fixed plant covers just about any structure on site that isn’t a building. Crushers and process modules, conveyor belts and their gantries, pipelines and pipe racks, solar panels, lighting towers, communications masts, signage, tanks, shade structures and walkways all carry wind load. And all of it has to stay put in a cyclone. Some are obvious. A large sign or a solar array is clearly a big flat surface waiting to catch the wind. Others are less obvious but just as exposed, like a slender lighting tower that can resonate. It might not blow away, but that intense resonance can damage the tower. Or a conveyor gantry whose length turns a moderate pressure into an enormous total force.
How cyclonic wind loading for fixed plant is assessed
Assessing cyclonic wind loading for fixed plant starts with the same standard as a building but asks different questions. We work out the design wind speed for the site’s region, terrain and shielding. Then the pressures acting on each surface and the way those pressures translate into forces, overturning moments and, most importantly, loads into the connections and foundations. Slender structures get checked for dynamic response, because a lighting tower or a mast can be driven into resonance or fatigued by repeated gusting long before it would fail in a single event. Where the geometry is complex or the standard’s simple cases don’t fit, we use finite element analysis to model the structure and see where the load actually goes.
The failures we’re designing out are rarely the member snapping in the middle. They’re the base plate, the anchor bolts and the welds at the connections.
Nine times out of ten it isn’t the steel that fails, it’s the fixing. The structure is strong enough. But the anchorage was never checked for the real wind load. Then the whole thing lifts or slides off its footings. Very dangerous.
Daniel Berti, Head of Mechanical Design, Element Mechanical Design
Testing and certifying fixed plant
There’s a difference between a structure that looks heavy enough and one that has been checked and certified. Element Mechanical Design assesses fixed plant for cyclonic wind loads to AS/NZS 1170.2, and where it complies we can certify it, giving you the documented engineering sign-off that operators, insurers and regulators expect before plant goes in on a cyclone-exposed site. Where it doesn’t comply, we tell you what needs to change, whether that’s the anchorage, a bracing detail or the structure itself, and we design the fix.
A certificate isn’t a rubber stamp. It means someone has actually run the numbers for that structure, on that site, in that wind region. And they’re willing to put their name to it.
Daniel Berti, Head of Mechanical Design, Element Mechanical Design
If you’re installing fixed plant on a Pilbara site and you’re not certain it stacks up against the wind talk to Element Mechanical Design. We can assess it and tell you honestly where it stands. We can tell you how it can be improved (if it needs it) and certify it when it’s right.