Rig safety

[Jamtastic3]

Hi all,

Well I'm needing some advice and opinions here really.

I was on another thread that talked about rigging scaff poles with hanging clamps:

 

http://www.doughty-engineering.co.uk/cgi-b...showprod_T32000

 

Now when I saw the SWL, it got me worried because the rig I work with in a live venue uses these hanging clamps to rig the entire rig from the roof.

So I'm basically needing some expert advice on the rig I work with. Below are some pictures:

 

http://i9.photobucket.com/albums/a56/Jamez3uk/DSC00282.jpg

 

http://i9.photobucket.com/albums/a56/Jamez3uk/DSC00288.jpg

 

http://i9.photobucket.com/albums/a56/Jamez3uk/DSC00292.jpg

 

The first picture shows how the truss is hung. The U shackle has a SWL of 1 ton.

In the second picture, you can see that there are 3 (of 6) x PS15's hung from the truss. This is how our FOH is rigged (it's the only way tbh)

The third picture is a view of most of the rig above the dancefloor.

 

Apart from the PS 15's hung from the rig, there are several moving lights, mirrorballs, parcans, black drapes and a roll up projector screen.

 

Now I wouldn't do this if I thought there wasn't a problem but I've been worried about the weight of the rig for a good few months now. The rig has been up for nearly 5 years now but the rigging points have been there since the 90's. We've had trapeze acts hung from the cross point (pic 3) and swings for acts at various point loads in the past. I asked for a heavily rated SWL safety bond at the cross point (with the existing hanging clamp and shackle), so that's the only thing I've done so far to make me satisfied.

I'd just like to know if I need to take any action about the rigging points.

 

Cheers

[johnhuson]

Without a scale drawing showing all point loads on the truss and showing number and location of rigging points, I think it would be a impossible to give you a definitive answer. Even then we would only be able to say if the clamp is suitable or not, no way of telling if the point above that is good for the load without a structural engineer taking a good look at it.

[Gareth Young]

Certainly the weakest link in your rigging chain would be the clamp that you use - SWL 75kg (If its the Doughty version and not some copy made of crap metal). So although the installed roof shackles may be rated at 1T, if there is going to be a local failure the clamp ring may be the first thing to go. Also, just because the shackle itself is rated at 1T, doesn't mean the way its fixed into the roof can deal with 1T (I can't quite make it out in the photo).

 

Further to previous answers however, its hard to provide an answer without first knowing what the total load is and how that is arranged; calculating point loads from that point on can then take a while to do as well: http://www.rigging.net/formulas.html gives you some starting formulas for this.

 

The PS15 datasheet on the Nexo site says it weighs 29kg, so three of them combined gives 87kg. On this area of trussing, I can't see any other up-rigging apart from the one ring you photographed and that load is slightly off centre to the point with other bits added on top (cables, PARs etc), so it could well be possible that you are exceeding the SWL of your fixing points - more information is required.

[kerry davies]

First things first, have you told the venue management that you are concerned about this? Reporting your worries on H&S is the law and simple common sense, unless you really do want to assume responsibility/liability. Next, I'm not a rigger but this is a job for an experienced/qualified/competent rigger if not for a specialist test/inspection company. (See many other threads)

The weakest link APPEARS to be the "O" ring in pic 1, it also APPEARS to be elongated?????But that cannot be stated as a definite from photographs. I wouldn't express an opinion that would have any real value, I'd get an expert to advise.

[Jivemaster]

Given a fully detailed drawing you can calculate all the loads applied to the truss and then adding the truss, the loads applied to the building. For each piece of the rig you can then determine the whether the load is within limits.

 

HOWEVER (and it's a big caveat!) Someone competent must determine whether the loads applied to the building are reasonable for where they are applied. The calculations for this will be beyond most entertainment riggers.

 

Perhaps a LOLER rating for the fixing points would be a good start.

[flypig]

My first reaction is to agree with Kerry and inform someone straight away.

 

I don't want to alarm you, but if I walked into a venue here in Australia and saw this rig, I would condemn it.

 

The ring on the clamp not only looks overloaded, but most certainly will be overloaded with that amount of gear hanging off the truss.

 

The rings are intended for flying light to medium loads only and should be discarded for a shackle for heavier loads (as indicated on Doughty's web site), with the pin of the shackle through the eye of the flying iron.

 

The point loads (fixing positions in the roof) need to be verified before any load calculations can be done (either the venue or the local commissioning engineer should have this information). Then, I would advise the venue spend a little money employing a professional rigging company to inspect the existing rig and calculate the loads for you / them.

 

Better they spend a little money now on safety than a hell of a lot more on too late compensation later!

 

Jamtastic3, I am a professional rigger with Pollard Productions here in Oz, and the images of that rig make my blood run cold.

 

IH

[LeeStoddart]

I have no competence in this area... this is just a question looking for more knowledge...

 

Is there a problem that the ring in picture 1 is "twisted"? What I mean is that it looks like the shackle at the top and the hanging clamp are not parallel so the ring can't be at 90 degrees to both of them.

[Seano]

Is there a problem that the ring in picture 1 is "twisted"?

It's not ideal, but unlikely to be a serious problem. I suspect that's why the ring appears to be elongated in the picture, I'm not at all sure it really is. The main problem apparent from the OP's pictures, as mentioned several times above, is that the ring most likely has a SWL of only 75Kg - a little bit less than the weight of the 3 speakers alone. If the ring really is distorted - that would be pretty serious, it would imply the hanging iron is already in the process of failing.

 

edit: Oops, just realised I wasn't actually addressing the OP.

[Jamtastic3]

Well tbh, the ring in picture one IS actually elongated.

Compared to the other points in the rig, this ring is more oval in shape than the rest. I discovered this back in Septemeber and immediately got the manager to clamp the end part of the truss (not in view but to the right of picture 1) to a vertical section of truss arch which surrounds the stage area. So now the truss is being supported at one end with a vertical truss piece but that's why I thought I'd ask on BR about this, going back to the initial review of the hanging clamp in another thread.

I've spoken to him so far about this concern and he says that he's going to deal with it.

 

If we were to replace the ring with an M12 shackle, this in theory would bring the SWL up to 250kg. Would this be the best idea or would a new hanging clamp of some sort be needed?

 

Just to say, the rigging points are attatched to the horizontal girders in the roof by some heavy duty 'scissor' style girder clamps.

[ed_]

Well tbh, the ring in picture one IS actually elongated.

 

IF the ring has stretched...

 

How many of these clamps are supporting the truss structure? I'm speculating here, but I'd be very worried if there is plastic deformation of the hardware, it means your factor of safety has been exceeded - to my (limited) knowledge no theatre hardware is designed to operate beyond the elastic range of the material, and the clamp has possibly only avoided failure by load redistribution.

 

Is it the centre point that has deformed, or the point above the speaker cluster? You may need to consider the effects of extra loading on your other points and extra bending in the truss: the load could have been redistributed due to the deformed point's inability to carry further load without significant deflection, raising issues that the truss or other points may now be overloaded.

 

For the avoidance of doubt, my only advice is to recommend, in writing, to the operator of this venue (I assume you are an employee of the venue, or a subcontractor who works there often) citing urgent concern for the safety of the rigging, the possibility of serious injury, and recommend that a suitable structural engineer assess the loading conditions at the earliest possible opportunity.

 

Personally, as a subcontractor, shown that venue I would not go near it - even if I wasn't flying anything - without a written opinion of safety of the hardware. When accidents happen, litigants tend to name EVERYONE in their suit... and even if you were in no way responsible for an accident, you could have to prove it and lose money in time and legal fees.

 

Sorry to be the voice of 'drop that contract' - but in the long run, it's worth it.

 

HTH - Ed.

[Stewart Newlands]

From the photos, their may be a number of other issues: ratchet straps while they are positioning speakers do they form part of the suspension and have they been de rated as lashing capacity is not lifting capability, over rigged lanterns using "hanging" hook clamps not designed for that type of suspension (do they have safety bonds?). Has the weight of the netting been taken into account and as it is tensioned what sort of forces is it applying to the truss?

 

This does need to be properly looked into on site by qualified Engineers / rigging professionals.

 

The Institution of Structural Engineers (IStructE): find an Engineer link

[musht]

Many years ago the rig ,at what is now the Cavendish Edinburgh, fell not long after refurbishment, suspension on one end failed and the whole truss pendulumed across the dance floor.Luckily the DJ wasn`t very good and the floor was empty, mo one was hurt.

 

If I remember the rumours at the time the rigging had been done by a Disco installer, still about, who at the time ,thought the way to clamp cable was put a half hitch knot in it and put a dog clip on to stop the knot pulling out.

 

Who installed yours................

[Andrew C]

http://i9.photobucket.com/albums/a56/Jamez3uk/DSC00282.jpg

You know, looking at that pic again, I'd guess that the ring is distorted because it has been twisted, probably deliberately.

The natural lie of the thing would be 90 degrees out when trying to connect to the D shackle.

[LeeStoddart]

You know, looking at that pic again, I'd guess that the ring is distorted because it has been twisted, probably deliberately.

The natural lie of the thing would be 90 degrees out when trying to connect to the D shackle.

 

See my post #7 above

[Jamtastic3]

I've been speaking to the manager and he is going to replace the rigging points with M12 shackles instead of the rings. It means we will have to replace the hanging clamps as well. It might mean we'll need another shackle after the first to complete the 90 degree turns (as some of you have pointed out).

So the plan is to replace the exisiting hanging clamps with new ones with a M12 shackle, then add another shackle and then attatched that to the exisiting 1T shackle that is attached to the scissor girder clamps.

 

To answer some questions that I know:

 

The rig is hung from the girders at 6 points. 3 off to the left of picture 3 (supporting the 2 truss' and scaff pole in the far distance) and 3 in the 'middle' of the rig (you can make out 2 of the points of the girder clamps in picture 3 from the visible girder line or line of 16A sockets). The truss and scaff pole heading to the left are attatched with aluminium scaff poles to each point, creating a grid. The ends of the other side are supported by a 2 sided truss 'arch' that surrounds the stage. It has 3 vertical legs that help support the rig nearer the speakers. One point is permenantely attatched into the wall. Anything else metal above the rig is ventilation and has nothing to do with the rig.

 

The PS15's are hung from the tops with heavily rated wire bonds that clip to the top of the Nexo speakers. The ratchet straps pull the speakers back to achieve dispersal and the angle of which the speakers need to be, but because Nexo don't design hanging brackets for PS15's, this is the only way you can achieve the somewhat 'best' angles for hanging the speakers. I can't tell you ratings of the the straps, though we've never had a problem with them in the last 4 years.

 

Everything in the rig does have a safety bond, I wouldn't rig it if it didn't. In fact the chains are cable tied to the lanterns as well so that they aren't stolen - it happens. I took the pictures with my camera phone so you can't make out the bonds on the Opti and pars.

 

On stage, the front parcans are hung 'upwards' because the speakers take alot of the area up on the truss. All lanterns use hanging clamps, there's no money to replace these with specific clamps for different angles.

 

The netting is hung loose and is very lightweight (and FT'd) so it doesn't contribute to straining the rig.