Is this structure safe?

Jeff Kenney

Freshman
Mar 4, 2013
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This is something I don't think I've seen before. I know we've had some pretty big scaff structures built in the past - but nothing like this.

Input? Is this legit/safe?

scaffstage.jpg
 
Re: Is this structure safe?

There appears to be balancing wires running vertically from the top beams, one can only assume they are connected to balancing weights. The roof structure doesn't appear to be very heavy, with only a moderate lighting assembly suspended from the roof, so it probably won't collapse if a mosquito farts on it, but I can't see it being safe for 70 mph winds
 
Re: Is this structure safe?

From a single photo at that distance, there are parts of the structure that would warrant closer inspection to be able to make a determination if it's safe or not. Nobody could look at that single photo and give a passing grade to the structure.
 
Re: Is this structure safe?

Too many people disregard possible wind load. They look at a roof and say, its not that heavy, just some truss and canvas.

But some "back of a unopened junk mail mail" calculation shows that a 20 mph wind at 30 ft above the ground in a generally open area may add up to 4000 lbs of force on the structure in just about any direction. If the wind were to gust to 60 mph that force could jump to 40000 lbs.

I have seen gust fronts blow every directions from straight down to bouncing off the ground and blowing straight up, so a structure would have to resist that in literally 360 degrees.

I am not involved in building these big stages enough to know if this exists, or if it is a regular practice, but I would like to see a roof skin engineered to tear away at a wind velocity low enough that it doesn't threaten the rest of the structure.

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Re: Is this structure safe?

I am not involved in building these big stages enough to know if this exists, or if it is a regular practice, but I would like to see a roof skin engineered to tear away at a wind velocity low enough that it doesn't threaten the rest of the structure.

At the Indiana state fair collapse, the roof tore away as per design, so it definitely exists. I remember seeing some load specific overload release straps that could be used for stage scrims etc., but haven't been able to locate them.
 
Re: Is this structure safe?

At the Indiana state fair collapse, the roof tore away as per design, so it definitely exists.
At the Indiana state fair collapse, half the roof tore away as per design, but the stage right roof skin side remained attached. The wind hammered the structure down faster than the speed of gravity, snapping critical lateral guy cables and straps and dragging weights that other guy cables were attached to.

As Jay mentioned, gust fronts blow every direction, in my back yard saw a thermal "dust devil" pick up a piece of 4x8" plywood and helicoptered it up around 60-80 feet in the air before it spun out of the thermal center and it flew 100' feet away, fortunately not damaging anything.

In another event, the steel roof blew off my guest house, cutting through my neighbor's power mains, the short circuit caused the town's main transformer breaker to trip. When I came home to find the electricity out, saw my fence was trashed, but had no idea the roof was missing until the next morning.

Regarding the O.P.s query, "is it safe?", my answer would be with no wind, it probably is safe, but wind is unpredictable, and worst case scenarios should be anticipated. The lack of any lateral guy wires is a grave concern with as much sail area present on the roof, advertising scrims and suspended PA.

Art
 
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Re: Is this structure safe?

I'm not sure there is enough information in that photograph to judge whether it is safe or not, so I think the best thing to do is not judge it either way and defer to an engineer.

The problem with this industry is that people who aren't competent to make safety assessments are being allowed to do so. And that works both ways....
 
Re: Is this structure safe?

1. It's safe for me to work only when I decide it is safe.
2. It's legal for me to work when all the papers are in order.
3. I don't work if #1 is not satisfied, an engineer's stamp won't bring me back to life.
 
Re: Is this structure safe?

One of the problems in Indianapolis was that the ballast (typical highway divider on grass) was insufficient - it was found that at the guy wire angles they had, it took only 2500 pounds of force to drag one across the grass.