Every outdoor rental quote I get asked to review argues about pixel pitch and brightness. Almost none of them contains a wind number. Then the wall goes up 8 m tall on a plaza, the forecast turns, and at 2 a.m. the conversation is suddenly about sandbags.
A rental wall is a sail that happens to emit light. The screen is the easy part. The rigging is where the money and the risk actually sit.
What "6-level wind" means in newtons
Beaufort 6 — strong breeze, the level where flags start snapping — is 10.8 to 13.8 m/s. Dynamic pressure is q = 0.613 × v², so that band is about 72 to 117 Pa. Multiply by a flat-plate drag coefficient of roughly 1.25 and take a 12 m × 8 m wall, 96 m² of sail:
- at 10.8 m/s: about 8.6 kN
- at 13.8 m/s: about 14 kN — 1.4 tonnes of horizontal push
That is not a storm. That is a normal summer afternoon in a city square, and the screen is being pushed with the weight of a small car.
The number that decides whether your wall stands is not the force, it is the moment about the front base line. The load centroid sits near h/2, so 14 kN × 4 m gives roughly 56 kN·m of tipping moment around the front edge of the base.
Ballast is an arm length, not a pile of weights
This is the part that gets skipped. Ballast resists overturning through a lever arm measured from the pivot — the front edge of the ground support. If the ballast sits 1.5 m behind that pivot:
- required ballast = 56 / 1.5 ≈ 37 kN ≈ 3.8 tonnes
- move the same ballast to only 0.8 m behind the pivot and you need 70 kN ≈ 7 tonnes
Same wall, same wind, double the ballast, only because of where the weights were placed. On a real site the ballast is usually whatever water tanks or concrete blocks the venue has, so the arm is the only variable you can still design. Push the base beams back, not just wider.
Two more things disappear from most site plans:
Gust factor. A 10-minute mean wind of 13.8 m/s carries gusts that are 1.5 to 1.8× the mean. The wall does not fail in the mean, it fails in the gust. Size for the gust, then set an operating threshold well below it.
The wall you build is not the wall you designed. Add the ground row, the side return, the cable ramp, and the cover left on overnight, and your 96 m² has quietly become 110 m².
Ground stack versus flown
Ground stack: the base beams and ballast take the moment, and every cabinet above the base is a lever arm. The failure mode is progressive — one loose base beam and the top row walks.
Flown from truss: the wind load goes into the truss legs, roof ballast and guy wires, and the wall becomes a lever on the truss rather than on the ground. You also inherit the truss's own sail area and the roof's. A flown wall at 8 m needs the rigging plan to show the truss, not just the screen.
Guy wires only earn their place when the anchor is real. A wire at 50° from horizontal takes roughly 1.3× the horizontal restraint it provides, so 14 kN of restraint means about 18 kN of tension in the wire — and that load lands on whatever you clipped into. Asphalt in August, a manhole cover, a fence post: none of these are anchors. If the anchor is not engineered, ballast is the honest answer.
What actually fails on site
Not the LED. In rough order of how often I hear about it:
- The bottom row sits in water. The cabinet is sealed; the connector is not a boat. Standing water at the ground row is the most common post-show failure.
- Corner cabinet twist. The outermost column takes the highest local pressure and is usually the last one braced. Two diagonal braces at the corners are cheaper than one corner cabinet.
- Clamps tightened by hand at 6 p.m. Truss couplers and base plates need a torque value and a second check after the wall is fully dressed.
- Cable bundles acting as a rope. A bundled catenary between the wall and the FOH position pulls connectors out of the first cabinet when the wall moves a few centimetres.
- The cover left on overnight. A tarp over an 8 m wall is a second sail, mounted above the first one, in the dark.
A pre-rig checklist that fits on one page
- Site wind data, not the city's average — exposure matters more than the number.
- Design gust, plus a written operating threshold and who calls the strike.
- Sail area including ground row, side returns and any cover.
- Overturning moment, ballast weight, and the lever arm written down separately.
- Anchor type confirmed in writing, or ballast only.
- Torque values for couplers and base plates, checked twice.
None of this is exotic engineering. It is one page of arithmetic that most rental quotes never include, and it costs nothing to add to a proposal — which is exactly why buyers should ask for it before they compare price per square metre.
The cabinets themselves are a solved problem at this point. A 500 × 1000 mm outdoor rental cabinet like the ARC2.604-H is a 12 m × 8 m wall in 24 columns and 8 rows — 192 cabinets, and 192 decisions about where the load goes. The hardware will hold. The plan is what fails.
Ballast only, or ballast plus guy wires — which would you rig at 8 m?
I work with MuenLED, a Shenzhen LED display manufacturer. #MuenLED
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