Why our outdoor stages are falling down.

In the last few years there has been a rash of outdoor concert stage collapses in inclement weather, epitomized by the 7 people killed at the Indiana State Fair before a Sugarland concert. Is this a phenomena? Coincidence? Or have things in our industry changed that are causing this trend?

Let’s go fly a kite.

Outdoor concert stages are all pretty similar structures. There is a deck, usually made of platform pieces that interlock with a cross-braced support structure underneath. There is a roof structure that the lighting and sound equipment hangs from which is covered with a cloth to protect equipment and performers from sun and rain, and there are support towers that hold up the roof, at least at the 4 corners of the stage, and for very large stages, there are usually more towers concentrated near the corners of the stage. The corners are guy wired into the ground to keep the hole thing in place. It kind of resembles this:

That’s a little unfair of a comparison, but there is some truth to the fact that there are just large amounts of surface area that the wind can push against on a concert stage when you cover it with fabric, hang a giant video wall in the back, and hoist it into the air.

That last part is the problem. The roofs of these stages are meant to come down during high winds, and design them as structurally sound as you want, but if you leave that roof up in 60 mph winds, there’s a good chance it’s coming down on its own.

But what’s different now?

The one thing that has changed drastically over the last decade is the amount of weight we hang from these structures. We used to light shows like this with a couple hundred 7lb PAR cans. Now we’re using at least a few dozen 40+ lb moving lights, but in some cases we’re using a hundred of those. We are supporting video walls that can weigh a half ton or more, and as stages and crowds get larger and larger, the number of speaker arrays (probably the heaviest thing up there) grows.

The weakest link….

All of that weight amounts to an incredible downward force on the structure. A structure made mostly of lightweight aluminum. There are folks who are arguing that Europeans are using steel and that it’s unconscionable that they we are not just because it’s lighter and cheaper to transport. They argue that steel is necessary to hold up all of that weight. Here’s the problem - any engineer analyzes a structure by it’s weakest link, and generally in a truss structure like this there are two things that must let go for everything to fall apart; the guy wires, and the truss bolts, both of which are already made of steel.

A wirey guy…

Guy wires are a very misunderstood thing. Most people think they are a safety that holds everything in place and keeps it from wiggling. That’s true, but I think we underestimate just how important it is to keep everything from wiggling. Technically, guy wires keep the entire structure from twisting out of true shape in any direction. When the wind blows on the big kite, most of the force is purposefully exerted on the guy wires, which keeps it off of the truss bolts. If the guy wires break (or don’t exist), the whole structure can twist out of shape, and as soon as the truss towers are ever so slightly out of vertical, all of the force from the weight from that roof (could be 10 tons or more!) gradually shifts from being directed down the length of the towers into the ground to truss bolts at joints that start to shear apart. Those big speaker arrays, which are generally held up by one point start to swing like pendulums putting more torsional force on the structure, and the whole thing falls over like it was made of twigs. In the picture below from the Sugarland concert, you can see where the truss towers have severed all at the same place, right where they are presumably connected with bolts to that shorter top piece:

What does all of this mean?

To me, it certainly doesn’t mean steel. I’m no engineer, but I think that’s just more weight. The truss itself doesn’t seem to be what’s failing. It might mean we need an entirely new type of structure. Or maybe it just means we need to size our guy wires bigger and place better emphasis on them. If a cable can hold up the Golden Gate Bridge, it can hold up an aluminum stage, as long as it’s sized and anchored right. That combined with strict weight limits on the roof, and maybe piling more speakers on the ground could save a lot of lives.

None of this matters.

What’s killing people is not guy wires. It’s good old fashioned excess. Look at that stage above again! Several tons of equipment is mounted overhead on a temporary structure that’s taller than it is deep!! It doesn’t take an engineer to know when something is top-heavy! Why does anyone think that’s OK? Our outdoor stages are just too damn big. You can’t build an arena outdoors. Stop trying. Build smaller stages. Stop expecting video walls and the same quality light shows (half the concert is always in daylight anyway). What has made outdoor festival concerts great is that they’re not arena shows, the focus has always been more on the music and the fun of being outside with nature and straw hats and beer listening to Lynyrd Skynyrd. If state fairs and festivals want stages this size, they need to build permanent structures. Or at least bring the damn roof down in a severe thunderstorm warning.