Double ended hook clamps

[Charlotte_R]

Hi,

 

I've posted about this before, but rather than bumping the thread, I thought I'd start a new topic.

 

My amateur dramatics group performs in a church hall, and their front bar is hung from a roof member by 3 double ended hook clamps; which makes me a bit uncomfortable.

 

At the top, the hook clamps are just hooked over the bar with no actual fastenings holding them there except gravity. At the bottom, the lighting bar is clamped in as per normal.

 

Is this safe? I honestly don't feel that I have enough experience to say whether it is or not; but my gut feeling is that it's not. I don't want to kick up a fuss if it is safe.

 

If not, I think we have two options to replace this setup: either replace the hook clamps with studding; or replace the whole thing with truss hung with chain motors. What would you advise?

[MarkPAman]

Previous thread is here with some sensible answers it it already......

[TomHoward]

For more in depth suggestions if it's possible it might be worth just snapping a picture of the bit that concerns you?

[paulears]

Hook clamps hung over the bar - with the thumbscrews present and tight, or missing and the whole bar wobbling?

[Charlotte_R]

At the top, the thumbscrews are missing and just hooked over a (wooden) roof truss. The whole bar wobbles when you touch it.

[paulears]

In that case - using my own set of rules, I'd declare it a proper risk. Lifting a bar off the wood is quite possible. I actually did it myself when somebody had rigged some lights from the fly rail, and I pulled a large A-frame ladder sideways into it and flipped it up and off. A bar would be more weighty of course, and the amount of effort to lift it off greater - but it could happen. The results would of course be worse. Double enders attached to a metal bar would work for me, but wood would concern me.

 

The wooden beam could well be perfectly sound and capable of supporting the load. It might not. Is it a fit and proper system that can have a rating of XKg put on it? Probably but not necessarily so. It will be ask the engineers time.

[Brian]

Some of these...

 

 

...some lengths of M10 studding, and some of these...

 

 

...job done.

[Charlotte_R]

That's my plan... Although I'm going to use some steel angle / plate to clamp the beam so that I don't have to drill them.

 

This is for two reasons: first, I'm not affecting the material structure of the building; and second, so that I can get everything pre-drilled on the ground and when I get it in the air, it should (hopefully) ease installation.

[Seano]

I'm going to use some steel angle / plate to clamp the beam so that I don't have to drill them.

 

Alternatively, you may find it more convenient to use a sling, a shackle and one of these:

http://www.deepsoup.f2s.com/BR/badgerclamp.jpeg

 

(Assuming, with a nod to paulears's comments above, that you're confident the beam is good for the load.)

[Charlotte_R]

The drop from the roof truss to the current lighting bar is about 1.5m (I'm going to measure it all next time I go up, in the new year). While I like the sling idea, won't that have potential to just swing?

 

Having said that, is there a possibility of hanging this so that the bar is easy to fly in and out so that we don't have to carry lamps up and down ladders?

 

Edit: I'm confident in the beam. It will comfortably hold the weight of the lights that we have hung on it and they're great baulks of timber, which seem sound. The roof seems, to my relatively untrained eye, hugely over-engineered.

[Brian]

...is there a possibility of hanging this so that the bar is easy to fly in and out so that we don't have to carry lamps up and down ladders?

 

If it moves then it fall under LOLER and is inspectable.

 

That said, bringing the bar down to ground level to rig is always preferable to going up a ladder. Which is right for you is for your risk assessment to consider

[timsabre]

Edit: I'm confident in the beam. It will comfortably hold the weight of the lights that we have hung on it and they're great baulks of timber, which seem sound. The roof seems, to my relatively untrained eye, hugely over-engineered.

 

A photo of this would be useful - if a hook clamp fits over it it can't be all that "great" a bit of wood.

Couldn't you just put a screw into the beam through the hole where the hook clamp bolt should be? That would stop it lifting off which seems to be the only potential risk.

[Seano]

The drop from the roof truss to the current lighting bar is about 1.5m (I'm going to measure it all next time I go up, in the new year). While I like the sling idea, won't that have potential to just swing?

 

Yes, it will swing. But it will do so without inflicting any damage on anything. On a 1.5m drop of threaded bar it will still wobble somewhat (as it does now, but hopefully much less alarmingly) - you'd need to be careful not to apply too much force to it as a rigid drop potentially gives you the leverage to bend the rod(s) or, depending on the design, to damage the fitting/bracket/whatever you have up at the top. You certainly wouldn't want to try leaning a ladder against it, for example.

 

Depending on the length of your bar, it might be worth looking into replacing it with a lightweight truss.

 

Having said that, is there a possibility of hanging this so that the bar is easy to fly in and out so that we don't have to carry lamps up and down ladders?

 

All things are possible, depends on your budget. ;)

 

The simplest approach to that might be to hang the bar (it would most likely need to be a lightweight truss to allow a reduction in the number of suspension points) on manual or electric chain hoists. And there would be an ongoing cost, significant but not enormous, for an annual (probably) inspection regime for those.

 

How often do you re-rig the bar? If it's infrequent, a 1.5m drop would give you sufficient headroom to temporarily rig hired hoists, lift the bar/truss off its dead-hangs, lower it to the floor and then reverse the process. Perhaps once or twice a year to give fixtures a thorough clean & service would be economic, whilst continuing to colour & focus from a ladder (or, perhaps better, scaff tower or some other form of access).

 

The cheapest and easiest way to eliminate carrying lamps up ladders is something you could be doing already though: temporarily rig a pulley on the beam above your bar using a 120cm climbing sling and a karabiner, and have someone on the floor lift & lower them on a rope.

[ontoprigger]

I'm confident in the beam. It will comfortably hold the weight of the lights that we have hung on it and they're great baulks of timber, which seem sound. The roof seems, to my relatively untrained eye, hugely over-engineered.

 

 

I would defiantly seek the opinion of someone with a trained eye, there are many forces on a roof truss that may not be apparent to the untrained eye, and many of them to do with the weather.

Another thing that you would need to consider in the raising and lowering system besides LOLER, is it will need to be to a higher safety factor as it is going to be left suspended over peoples heads see BS7905 & 6 as a guide, but unless otherwise specified in the risk assessment you would need a minimum of 8:1 (and if specified lower you would need a pretty good reason why if it all went wrong some day).

You also need to be aware that the forces imposed on the structure will be higher, as you will have over double the lifted load on the structure as the force required to lift the load will be equal to the load plus about 5% for friction, so at the point where you pull from you will have a much higher point load than anywhere else in the system, so if you could mount that on a wall rather than the beam all the better..

[chrisdwalker2002]

Hi Charlotte,

 

I never heard back from you regarding me coming down to have a look and quote on this for you. Were you still interested at all?

 

Cheers.