Accident

[avdavesound]

OMFG!!!!111 They're using truss to support a roof AND lighting. It's a death trap. They should have gone to riggit.

 

*cough*

 

Sorry.

 

 

Incidentally I was discussing that style of upright with an American rigger just the other day as they're apparently used quite frequently over there, there's even one company marketing them to the entertainment industry for that very purpose.

they look like the new vmb line array lifters good for lifting up to 250kg. look Here. never seen them used to lift a roof/parachute before! death trap

[charlyfarly]

Totally daft......and dangerous. The structure the units are hanging from is just a gazebo really. Would you? No thought not!

[Ike]

Oh come on this is just getting stupid. Not only are these comments poorly researched but they are clearly libel as you have no way of proving your comments never mind everything implied by the poor choice of wording. I'm not suggesting we shouldn't jump to snap decisions based on little 'evidence' but to post it on an industry forum seems at best pointless.

[paulears]

Nobody in the topic has made any mention about the manufacturer - just a link to something 'similar'. The text of the article states the tent fell down - so no technical info there either. The res of the image is pretty poor, and I can't make the larger image work for me. The physics is pretty clear, however. If you built this from lego, it would fall down. I'd guess that a 1st year design student would identify a number of problems with the design, based on the photo. I doubt more info will be available for a while. Perhaps in the interests of fairness, we should close the topic as it has generated some concerns? Opinions?

[Ike]

Not mentioning the companies name doesn't make it any less defamatory.

 

The lifts are not made by genie and are actively marketed for use outdoors. The lifts were not the point of failure and the collapse could have still happened if it was similarly attached to truss legs. The presumption that it was bound to fall down seems daft as this system has been used thousands of times before and has not done so as far as I know.

 

I'm not trying to stick up for the company and I do think serious questions need to be asked but speculation and use of language like "death trap" at this early stage can't help anyone. It is libel, it is unprofessional and it is wrong.

[indyld]

This topic was commenting, not only on the accident but the reporting of it etc.

 

I can't say I have seen much in the way of defamatory remarks in the various opinions stated and perhaps the topic has run it's course.

 

I agree that the focus on the make/model of lifts used is a bit unhelpful and it actually misses the point. From the way the roof seems to have failed, they do not look to have been the root cause. As Paul rightly pointed out, a 1st Year Design student could have seen the weaknesses at the apex that have been discussed and I have to disagree that there has been an incorrect presumption of the roof failing, simply because looking at the other roof pictures ("before" - even if they are speculative) such a failure was pretty predictable. The type of legs used to hold up the canopy - truss, lifts, RMD, Manfrottos, Tallescopes or whatever you like, doesn't change the dynamics much in the case of this apparent failure.

 

Also, just because something has been done before, doesn't make it any better.

 

I think that everything has been said on this topic until we get any more information.

 

Unless a rigger would like join in and tell us that they would have been happy to put that roof together. ;-)

 

//edit: After thought - Anyone who has, like me, spent the recent past in the company of some professionals (plumbers in the house - insert your own: builders, car mechanics, riggers, etc) will know that rubbishing other peoples work is about as professional as you can get. ** laughs out loud **

[Ike]

I can't say I have seen much in the way of defamatory remarks in the various opinions stated and perhaps the topic has run it's course.

Really?!

 

As Paul rightly pointed out, a 1st Year Design student could have seen the weaknesses at the apex that have been discussed and I have to disagree that there has been an incorrect presumption of the roof failing, simply because looking at the other roof pictures ("before" - even if they are speculative) such a failure was pretty predictable.

I don't see how you can say the failure was predictable, a few back of a matchbook calculations using visually similar truss, estimated distances and loading show the system is more than likely operating well within the minimum breaking strain of its components.

 

Also, just because something has been done before, doesn't make it any better.

No it doesn't but saying a roof cannot stay in the air when it has done many times before is clearly not correct.

 

There are a million and one reasons why things fall down. If you really want to speculate why not talk about the possibility of human error during erection or what the people on stage were doing at the time?

[Wuddy]

Going by the information supplied in the two pictures and if the collapsed structure is of the same design as erect structure then there is a inherant design fault.

 

With any pitched roof design there has to be a force equal or greater than the roofs weight and load acting against the eaves line.

The weight of the roof and any load is trying to collapse itself by pushing apart the lower eaves edges.

The eaves edges should either be tied across to each other to prevent spreading or buttresed up from the ground, this tying or buttressing structure is not visible in either picture.

 

In the first pic in order for the roof to collapse like shown it must have pushed apart the vertical supports, the slopes of the roof are basically the hypotenuse sides of two RA triangles their combined length being greater than the width of the stage, to end up as shown they have had to pass throught the horizontal position which could only happen by pushing apart the verticals.

 

This is an easy one to try at home by propping up a couple of books to form a ridge, without something to hold the lower edges they will just fall down almost certainly under there own weight.

[Goran Mitic]

Hey, I sure did learn a lot, so thanks to all for input.

 

The thing that got my attention was the cover up story with pizzas.

And, of course I was interested in why the roof 'folded' like it did, so I opened the thread.

I am for no speculations, but one can not without having a thought.

My first 'speculation' was too much of load, with maybe a bit of wind. And with every next look, I had a new 'speculation'.

I think many, if not all, possibilities have been stated here. It was good thing to hear.

 

I used to work for ground support company which course of outdoor roof assembly is an adventures one (well indoor too for that matter) . And since here (Slovenia + Croatia) are no inspectors or inspection/safety regulations (or even proper knowledge) on 'rigging safety', the stress on assembly components and material is constant factor, and we got away with a bunch of things. Plus our mistakes, breaks,... And we did some big shows, Depeche Mode, Marlin Manson, Joe Cocker, Pavarotti,...

 

I loved doing dangerous job (assembling outdoor structure/roof , climbing, and just loved when it rained), but I got scared as I learned we were doing things wrong, in unsafe manner. Therefore accidents. And this is no speculation.

 

So, I don't think it is bad pointing out some specifications on same or similar components (geenie/lift, ground/grass, trusses, wind), or how they are bind together. What most, give the one who binded that thing together a fair warning! Hey man, someone could die. There were injured people.

 

Fun should not be deadly. Making profit by cutting edges is adventures course.

[indyld]

The eaves edges should either be tied across to each other to prevent spreading or buttresed up from the ground, this tying or buttressing structure is not visible in either picture.

 

Apart from the black strap holding the banner on the upstage gable end in the "complete" picture (don't get me started on 180 degree bridles!!). Perhaps the U/S banner was not yet rigged on the hapless roof. Oops, I forgot that the Blue Room is not the place for half-a*sed opinion and ill informed speculation....

 

Thanks Wuddy for taking the time to put what we are all thinking to the screen on this topic, I'm afraid I am just too lazy. I have rigged many similar coverings and they have all included one or more of your elements in the form of truss, steels, ratchet straps and/or outriggers in some shape or form. Having learned rigging on the job with good people, all I know is that none of the really good riggers that I have worked with would think much of that roof picture, even if the stage was still standing up.

 

Rigging is a job that used to start with the knowledge and instinct of an experienced rigger who then got the calcs out to prove/confirm what they knew already. Perhaps we have started to point the finger at spec sheets and tables instead of sticking our necks on the block and saying "I am going to be able to sleep well tonight because I am happy with that structure", which always used to be the test.

Anyway, am drifting off the point.

 

Having a snoop about the 'net showed up drawings for similar roof systems, possible the same one, which were notable by the inclusion in every case of a few more vital parts that provided the eave to eave stabilisers (under tension) and some support for the ridge (under compression). The addition of external guy lines, while helping out to avoid a "flatpack" of the legs, do nothing to keep the ridge from pushing the eaves apart.

 

Dangerous uneducated speculation? We are talking about what we see in the pictures.

 

Could I sleep at night having designed that roof? NO.

[paulears]

Let's ignor speculation and consider truss and loads. I'm certainly not an expert, but have what I hope is pretty good common sense. I don't have enough knowledge to work out the forces involved, so what follows is generalisation and guesstimates. Look at these two structures. Top one first.

http://www.eastanglianradio.com/trussangle.jpg

Ignoring any possible forces from the sides, then assuming this is 50mm od tube, then the weight of the truss and equipment is reliant on two welds (assuming the truss is either 3 chord, apex up or 4 chord box truss). I guess the two outer welds on the support would also be in the figures somewhere, but if the roof was simply sitting on them, rather than rigidly fixed, then I see just two welds holding everything up.

 

My question is that surely even to the structurally ignorant like me - there is something wrong with the design. No doubt with engineering, this design could be made to work, but the bottom one would seem to be inherently stronger, with all the horizontal chords under tension from the load the roof puts into the structure. Without the horizontal element I fail to see how the structure really works. It would seem that adding a load to the top version is daft. I can't do the maths - but I'm pretty sure that my decision is sound. This is what I meant by my 1st year design comment. I'd guess that this is basic stuff to people studying mechanical engineering. Can anyone suggest a way to make the top one stronger, wiithout tieing the uprights together in some way? No doubt people will also be considering all the other forces on the structure - I'd like to consider this design - ignoring the original post - so we can chuck in comments without worrying about the real life one? I may have made a simple or critical error here - I'd love to hear some comments on how right or wrong I am.

[jjackson]

hi folks, nice site you have here.

 

just want to clear a few things up. the truss was only holding a couple of dozen pars a few bits of cable and tube and was under its safe maximum load. the roofs are regularly used all over the US without any accidents. it failed because some of the truss pins were missing and someone had lent a ladder again one of the bits of truss and was overreaching.

 

paulers is right about the first diagram being stronger but it wasnt holding enough weight to need it. if the wind picks up the procedure is to clear the stage and lower the roof.

 

eric - the guy on the ladder is still in hospital and is stable and we wish him a good recovery

 

thanks

 

jj rfl

[djw1981]

I know nothing about rigging, but going back to first principles of structures (from high school introductory CDT), a triangle is the strongest structural shape. IIRC this is because to get one side to deform, you must deform all 3 angles and both the other sides. Thus the second diagram is the strongest, although where that to be a side or rear elevation, I would want an X of steels / ratchet straps across the 'square' wall to create 4 triangles, and keep teh parallel vertical truss parallel to each other.

it failed because some of the truss pins were missing and someone had lent a ladder again one of the bits of truss and was overreaching.

So why had a soundcheck been allowed to take place, if the structure was not safe? Were the joints /pins not checked before the structure was lifted into place? It is a point which I guess most Risk Assessments wouldn't cover because most people wouldn't think that you would lift a truss which was not pinned correctly.

[Wuddy]

hi folks, nice site you have here.

 

just want to clear a few things up. the truss was only holding a couple of dozen pars a few bits of cable and tube and was under its safe maximum load. the roofs are regularly used all over the US without any accidents. it failed because some of the truss pins were missing and someone had lent a ladder again one of the bits of truss and was overreaching.

 

paulers is right about the first diagram being stronger but it wasnt holding enough weight to need it. if the wind picks up the procedure is to clear the stage and lower the roof.

 

eric - the guy on the ladder is still in hospital and is stable and we wish him a good recovery

 

thanks

 

jj rfl

 

I'm so glad you've cleared thing up, most of us in the BR thought your roof structure was unsafe.

 

.

[David Buffham]

the truss was only holding a couple of dozen pars a few bits of cable and tube

I'm sure the 2nd from last of these photos also shows moving lights on the US side of the truss, but that might be an illusion?