Girder clamp advice

[Electrolytic]

Hello, a venues current Lighting rigging is not existent needs improvement.

 

I want to install two scaff bars running up and down stage, on either off stage. To then run three across stage LX bars, using again scaff or Gas pipe. The LX bars will be raised on 'A' frames into the voides between the beams. And an upstage tabs bar.

 

The venue is in a listed building basement, the ceiling is low at stage level, there are many girders/RSJ's overhead.

 

 

All the girders in question run across stage.

There are three girders above the stage, the centre one is an older type with rivets, the other two are modern. The centre one is not as low as the modern type.

The furthest down stage is modern type girder in the advance LX bar position.

 

I want the scaff bar to run from the very upstage to the advance bar position at the girder.

 

The ceiling is low on stage and this 'mother grid' is an attempt to solve the problem of 'pinch' clamping lamps to the existing girders which means there are head height and no good.

 

I want to put points on the girders. However due to the ceiling height I want these points to be low profile, ie big heart shaped 1ton girder clamps are not suitable, something like a kader clamp.

 

My question is are kader clamps acceptable to be used on girders or marquee box only?

Can kader clamps be used with a riveted flange?

 

each LX bar will only be taking 4-6 LEDpar cans / or simliar so kader SWL seems suitable.

 

However I would like to go over the top on SWL incase somebody does pull ups off the scaff bar 'mother grid'.

 

 

What are these called they look substantial and on the permeant side. Could a longer bolt be used to get a tube clamp down to the right height as the modern girders?

http://versales.com/ns/theatrical/images2/beam_and_clamp.jpg

 

 

 

 

 

 

 

 

 

 

 

 

 

What about Gravlock Couplers? are they ok? could these be used on the modern beams?

http://ecx.images-amazon.com/images/I/41sOLe5gYfL._SX466_.jpg

 

 

downstage view of venue:

 

 

any advise appreciated

[Shez]

What's the construction of the ceiling itself? Would you be able to get fixings in to that? I'm just wondering whether you could gain a bit of extra height by mounting bars to the ceiling rather than below the RSJs.

[TomHoward]

We use Gravloc couplers all the time as per your illustration. If the pipes are to run 90deg to the RSjs they are the easiest low profile way.

They need to be used in pairs (like the drawing) and from a scaffold supplied (EG Harsco/SGB) you can get them significantly cheaper than Flints.

There is also an older style Doughty girder clamp which is more suitable than kader clamps for a single fixing point:

http://www.doughty-engineering.co.uk/shop/images/products2/t29800.jpg

 

Your venue images don't show by the way which I guess might be a Facebook permissions thing.

 

Sorry about that - your venue images do show - it was a Facebook permissions thing but it was at my end - Facebook is banned on work internet. Forgot that bit.

 

It looks like there's an approximation of a gravlock coupler on there already, with a half coupler bolted onto a small adaptor - I don't see how gravlock will be an improvement over those?

[boatman]

I'm not a qualified rigger, but it seems to me that you could gain some height by mounting two pairs of Gravlok couplers upside-down with two short lengths of scaff pipe between beams and then mounting a pipe parallel to the beams on top of that. The parallel pipe would then be almost at ceiling height.

 

You would need to do some load assessment calculations, but there's no reason why it wouldn't work.

[Dave m]

Also not a rigger but agree with boatman

You won't have much headroom unless you make use of the space above the bottoms of the beams.

[Electrolytic]

What's the construction of the ceiling itself? Would you be able to get fixings in to that? I'm just wondering whether you could gain a bit of extra height by mounting bars to the ceiling rather than below the RSJs.

 

I guess its super solid concrete. I don't think construction work will be feasible because that will require some serious equipment. I don't know the correct procedure for making a hanging point, it would have to be signed off by a structural engineer. The building is Listed so a semi-permanent system working with the current structure is less hassle.

 

We use Gravloc couplers all the time as per your illustration. If the pipes are to run 90deg to the RSjs they are the easiest low profile way.

They need to be used in pairs (like the drawing) and from a scaffold supplied (EG Harsco/SGB) you can get them significantly cheaper than Flints.

There is also an older style Doughty girder clamp which is more suitable than kader clamps for a single fixing point:

 

Your venue images don't show by the way which I guess might be a Facebook permissions thing.

 

Sorry about that - your venue images do show - it was a Facebook permissions thing but it was at my end - Facebook is banned on work internet. Forgot that bit.

 

It looks like there's an approximation of a gravlock coupler on there already, with a half coupler bolted onto a small adaptor - I don't see how gravlock will be an improvement over those?

 

Thanks for the supplier info.

 

The current gravlock flange pinchers are only small, those bigger Gravlocks have a much hight SWL. I would lie to go over kill on the SWL of the fixing points.

 

I'm not a qualified rigger, but it seems to me that you could gain some height by mounting two pairs of Gravlok couplers upside-down with two short lengths of scaff pipe between beams and then mounting a pipe parallel to the beams on top of that. The parallel pipe would then be almost at ceiling height.

 

You would need to do some load assessment calculations, but there's no reason why it wouldn't work.

 

I see what you are saying but then each bar would only have two points and a single gravlock on either end when they should be used in pairs. If one end started to list the bar could twist out of true and potential fail.

 

Also not a rigger but agree with boatman

You won't have much headroom unless you make use of the space above the bottoms of the beams.

 

I want to run two bars from upstage to down stage. Then on top of these main bars, run across stage bars that are raised into the cavity via an A frame inside each bay.

[adamharman]

I see what you are saying but then each bar would only have two points and a single gravlock on either end when they should be used in pairs. If one end started to list the bar could twist out of true and potential fail.

 

The reason they should normally be used in pairs is to prevent any movement in the scaff tube from pulling them off the beams. If you use boatman's suggestion and cut the tube to be a tight fit between the beams then there is no possibility of end-end movement of the tubes. With bars across the stage clamped between them, you create a rigid rectangular frame that can't possibly fall unless something manages to bend the whole lot about a foot out of square. The strength of the tube and clamps, plus the bolts holding the gravloks to the beam, will make that highly unlikely to happen. You could put a pair of those small clamps either side of the gravloks as a precaution if you're really worried about it.

[TomHoward]

I did think about that too, that over-rigging the Gravlocks and cutting scaff pipe to fit within the distance between the beams would buy you that extra headroom. Admittedly though we're only talking about the region of 75-80mm difference at the bottom of the bar - as it'd be the width of the bar, plus the thickness of the RSJ flange, plus 2x the 10mm or so spacing between gravlock and flange. However, every little helps...

 

The gravlocks ideally would be used in pairs (always use in pairs!) but I have to admit with the loading and the advantages of headroom I'd be happy enough I could risk assess out the problems - a weekly check that the gravlocks are tight, or similar. Caveats that this is all subject to your own judgement and I'm a renowned bodge engineer anyway - so anything I advise should certainly be taken for entertainment value only.

[boatman]

Yes, that was what I was suggesting. Something like this should work:

 

http://mydesk.myzen.co.uk/_Useful/OverRigPipe.jpg

 

There will always be a pair of Gravloks on each short pipe, they will just be on different I-beams!

[Jivemaster]

I'd consider making a frame of two tube truss that fits exactly inside each structural girder, then you can hang lamps from the top tube, or a scaf across the top tubes. Being a non rigger I'd get a rigger or a structural engineer to calculate the loads and lengths.

[TomHoward]

I see - the grey indicates another pipe running left parallel with the front stage edge to create a cross-stage bar?

That's cleverer still because it gets another 80mm or so up. I'd assumed hanging points were all that was needed so the bars perpendicular to stage would do. The second bar running across would stiffen up the bars with interpretive use of gravlocs as well.

[boatman]

If there's concern about loading there could be three (or more) short pipes between the I-beams along the length of the stage-parallel long pipe. As Jive master says the short cross pipes could be made of two-tube truss which would make them even more stable.

[Jivemaster]

My plan started as simply a rectangle of two tube truss cut to fit INSIDE the girders then assembled in situ. Then perhaps a scaf bar on top of the frame or a beam of two tube truss fitted to hang lamps from. Even so you'd need good short fixings and any hot lantern would blister your listed paint.

 

Ever thought of getting coloured LED strip secured to the ceiling, and driving it properly, that's only 5mm thick and it's cool. -Covers colour wash but doesn't do movement or beams.

[Electrolytic]

some measurements taken will update.