Temporary Stage Collapse at Indiana State Fair 1

[Forensic74]

http://www.cnn.com/video/#/video/us/2011/08/14/hall.in.state.fair.stage.collapse.cnn?iref=allsearch

In the wake of the stage collapse at the indiana state fair, what are the design requirements on this type of structure? Are they even inspected??

 

[BAretired]

It probably depends on the jurisdiction. They should be designed for full wind load just like any other structure and the work should be inspected.

BA

 

[Forensic74]

I found this interesting article on temporary stages. Seems like it's not so straightforward.

http://www.structuremag.org/article.aspx?articleID=833

 

[IDS]

From the link:

"Accordingly, engineers are designing temporary structures that are strong enough to survive a once-a-century hurricane when in fact they will be used for only a short period - sometimes just a day or two - and would never be used to shelter people during a strong storm. The most these structures are likely to face is a thunderstorm, but the building codes call for designing for hurricanes, which drives up costs unnecessarily without increasing safety."

I disagree, and agree with BA.

These stages for mass popular events have the same useage as a stadium and the same consequences of failure, so they should be designed to the same standards as a permanent stadium. The fact that they are moved around between uses is surely grounds for additional caution, not reduced loading.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Ron]

MM10...BAretired is exactly right. If the stage in Indianapolis had been designed for the code winds (90mph) the 60 to 70 mph gusts as reported would not have been a factor. Couple that with adequate inspection and you have 5 people still alive rather that a large group of grieving family members. Sad that such is allowed to happen.

 

[Marksen]

There was already a thread open on this topic at

http://www.eng-tips.com/viewthread.cfm?qid=304714&page=2

where I quoted a European company which said it was using the German DIN4112 standards.

There is an interesting 2008 article on the US standards for wind loads on temporary structures at

http://livedesignonline.com/theatre/mighty_wind_load_1008/index.html

 

[Marksen]

I was also wondering if there should not be a strong requirement to be equipped with an anemometer, to know the exact wind speed, as you have on the top of tower cranes.

 

[JAE]

Marksen - that is a good article that provides an overall discussion of the issue. They also refer to ASCE 37 which I was going to mention.

For short term duration wind loads, a smaller (statistically speaking) wind load might apply. However, ASCE 37 uses a time duration of the structure to determine the wind load reduction from the standard 90 mph.

For the case of a traveling stage rigging, what is the time duration? I wouldn't necessarily say it was just the 3 days or 1 week that the concert was occurring. But as it moves around the country, it is constantly exposed to the wind and perhaps has the same statistical exposure as a 10 month structure, or a permanent one.

 

[msquared48]

"But as it moves around the country"

In that statement is the problem. Different juristictions, different requirements, BUT FOR THE SAME STRUCTURE. This is not a normal situation necessitating professional consultation, not some backyard podunk musician's trainee.

I apologize for my french...

Mike McCann
MMC Engineering

 

[firai]

The requirements depend highly on the local jurisdiction. I know some colleagues who specialize in stage work engineering, but there are surely many temporary structures out there that haven't been engineered, reviewed or inspected.

As a side note, from a public safety point of view, I would agree with BA, Ron and others and advocate that temporary systems should be designed for the same magnitude of loads as buildings. Although many temporary structure designs have the disclaimer that they must be taken down before adverse weather conditions occur, many irresponsible contractors disregard the advice. Therefore, the structures are still subjected to the same loading risk/probability at any instance of time and should be designed as such (without regard to how long the structure is used).

Structural Design Engineer
New York, NY

 

[hokie66]

Agree with others that temporary structures of this nature should be designed, constructed, and inspected to the same strength standard as permanent structures. Provisions requiring partial or complete disassembly before the high winds hit are ridiculously impractical and unenforceable.

 

[ishvaaag]

... and then is when the matter becomes interesting from an engineering viewpoint, since such opinions suppose a direct hit at the line of flotation of what is assumed as "acceptable" risk, as related to the temporary nature of the works and lower likelihood of the extreme event being met.

Certainly some simple importance factor changing how to could signify a safer design through other rules. But for temporary what we see are waivers, exceptions, more than anything. Philosophically, it looks as if construction wants to retain not only gains from risky business, but a reputation of still being so through lamentable particular cases like the one causing these comments.

 

[Marksen]

Agree with others that temporary structures of this nature should be designed, constructed, and inspected to the same strength standard as permanent structures. Provisions requiring partial or complete disassembly before the high winds hit are ridiculously impractical and unenforceable.

Tower cranes are temporary structures with regulations that require putting them into free slew under strong winds. And it seems practical and enforceable.

Perhaps stronger regulations should be decided for temporary structures which involve the presence of the general public, and even stronger regulations if this general public is a crowd with hundreds of people of more.

Mr Gorlin's comparison with umbrellas or even market tents in

http://www.structuremag.org/article.aspx?articleID=833

is a bit hard to swallow because their weight is much smaller than that of the music stage we are talking about and they cannot harm so many people at the same time.

It seems impossible to have one single regulation that would encompass all temporary structures.

 

[hokie66]

Tower cranes are allowed to freely slew whenever unattended. An entirely different thing than dismantling a structure or parts thereof with limited time after a severe storm warning is issued.

 

[Grahammachin]

In a previous company we did a lot of design work for stages, generally we designed in accordance with The IStructE "Temporary demountable structures. Guidance on procurement, design and use"

In the document it stipulates a minimumn wind speed for which a temporary structure should be designed based upon it's location, time of year it will be in place and length of time it will be in place.

A management regieme was to be in place with Anemometers measuring wind speeds (gusts not average). At certain wind speeds ie. 60% and 80% of max design wind speed (whether this is as specified above or the maximum the weakest member can accept) the following would be carried out.
At 60% staff whould be put on alert that action may be required.
At 80% with an increasing trend, cladding would be removed and the site would be secured against access by the public within specified zones (ie areas around the structure into which it may collapse).

 

[Grahammachin]

I should note this is in the UK not the US

 

[JLNJ]

In true fair/carnival carney fashion it was a game of chance.

Sometimes we play the odds...and don't win.

 

[Forensic74]

I think that it may be acceptable to design temporary structures around masses of people for less than full design wind only if its made very clear that it has been done so. I bet that the fair officials weren't made aware that the stages were only good for a limited storm.

 

[csd72]

I disagree with others that support designing these for full wind loads.

Even a reduction from 90mph to 70mph would result in only 60% of the pressure and huge cost savings.

Hurricanes dont form in minutes, there are usually quite a few hours of warning for which the site can be evacuated.

I think that there is definately a case for nationalised standards that can be waved in front of the local official.

 

[JedClampett]

I kinda, sorta agree with the concept of designing for reduced winds based on statistical models, evacuation procedures and disassembly requirements. But in this case, the reports say that the structure failed at 60 mph. That means it wasn't designed for 60 mph, but a wind load even smaller. This wasn't a hurricane moving in from the coast, taking days to develop, it was a midwest thunderstorm that happened suddenly. The crowd either felt safe under the shelter or had no place safer to go.
If it was correctly assembled (a big if), I suspect that the forensic study will show it was safely designed for some wind of a magnitude of 45 mph.