Lighting Bar Hangers - seeking

[MusicalMuseum]

Hi there,

 

My apologies for intruding with what is probably a very basic question!

 

I know there are lots of ways to hang bars from I-Beams but these are the ones we have - for safety, we want to add more of them to support the bars better and spread some extra weight that we are adding, so they need to be the same type & height.

 

They grip the I-beam ledge on either side, with a metal bar underneath, a short length of screw rod hangs from that, then the bar clamp.

 

I seem to have looked everywhere but I cannot find them.

 

Link to a photo here (hope it works): My link

 

Does anyone here know what these are called, and/or (ideally) where I could get them from?

 

Many thanks in advance,

Simon

[p.k.roberts]

I'm not competent to comment on their suitability, but they appear to be a type of Unistrut beam clamp;

 

https://www.unistrut.us/product-details/p1796s

[sandall]

It does indeed appear to be Unistrut, which is effectively Meccano for grown-ups & gets used everywhere. https://www.unistrut.co.uk/

 

Your local mechanical engineers should have no trouble sourcing the bits you need.

 

E2A: As you are a fairly new build you presumably should still have the paperwork for the bars.

 

 

Edited October 24, 2019 by sandall

[MusicalMuseum]

@p.k.roberts Thank you so much - Unistrut window beam clamps is exactly what they seem to be.

 

@sandall we do have a lot of architectural paperwork but it does not refer to these fixings, which were added by the team after the shell of our building was constructed. The bars in question were used for some fairly light-duty occasional loads, but will now be permanently equipped with heavier fixtures, and I wanted to be 100% sure we're safe.

 

I am much happier now that I know the design rating of these; and it appears I was being over-cautious - a single bracket is rated for 200Kg+, well over twice the load we will be adding on each half-bar, and there are three brackets sharing the load equally. I think the bar would fail before the brackets did!

 

We will still source some more for future use. I've also arranged for some professionally qualified riggers to inspect our work.

 

Many thanks for your help!

[bradleypallister]

Hi there,

 

My apologies for intruding with what is probably a very basic question!

 

I know there are lots of ways to hang bars from I-Beams but these are the ones we have - for safety, we want to add more of them to support the bars better and spread some extra weight that we are adding, so they need to be the same type & height.

 

They grip the I-beam ledge on either side, with a metal bar underneath, a short length of screw rod hangs from that, then the bar clamp.

 

I seem to have looked everywhere but I cannot find them.

 

Link to a photo here (hope it works): My link

 

Does anyone here know what these are called, and/or (ideally) where I could get them from?

 

Many thanks in advance,

Simon

 

Hi try code ref 12161 from www.kernow-how.com - they keep them in stock

[DrV]

Bradley, Simply changing the word "they" to "we" would put you back within the accepted practice for the forum.

[ImagineerTom]

a single bracket is rated for 200Kg

Just to jump in here - you need to check if that's the maximum load or the "safe working load" for these brackets or indeed anything else you ever use for rigging things over people's heads. A SWL is usually allowing 300% safety factor (ie something with 100kg SWL is actually designed to withstand 300kg) right up to an 800% factor depending on the product and manufacturers tolerances. This is especially important in theatre because of all the incidental forces applied whilst doing the job as a whole - suppose you had a bar with a maximum load of 200kg, you have 150kg of "lights" already on it and you decide to add a 30kg moving light; because it's heavy you use a rope and someone pulling on the ground to lift it up.... you're almost certainly going to be well over the maximum load for the part because a) everyone forgets or underestimates the weight of cables/clamps and b) the dynamic load caused by someone on the ground pulling the rope that goes up over the bar can easily exceed 30kg weight of the object so you potentially have a problem. Conversely if the bar you're rigging from has an SWL of 200kg then you don't need to be too concerned about going (briefly) over-load because there's a safety factor built in. There was an incident at Ringling Brothers Circus a couple of years ago where a dozen aerialists hanging from a frame were dropped to the ground suffering life changing industries - after all the investigations the main factor was that someone had used a component rated at XXXXkg and assumed that was actually its SWL so didn't take in to account the extra forces applied by the moving performers nor the inevitable decline in the parts strength as it sustained wear and tear.

There's also added complexities that loads don't distribute evenly to the pick up points used so even if you have got a bar with 3x200kg SWL clamps on it that doesn't mean you could hang a 600kg object from the bar (unless it was multiple objects, evenly distributed and the bar itself was very strong) this is why there's lots of specialist engineering firms with expensive computer simulation software to calculate what really happens with the forces in play.

I don't want this to sound like I'm criticising you in any way - by admitting you were not sure and doing some research you are already more safe and more sensible than the majority of people, I just want to make sure that no one else reads this little bit of knowledge and misuses it somewhere else

[sunray]

a single bracket is rated for 200Kg

 

Just to jump in here - you need to check if that's the maximum load or the "safe working load" for these brackets or indeed anything else you ever use for rigging things over people's heads. A SWL is usually allowing 300% safety factor (ie something with 100kg SWL is actually designed to withstand 300kg) right up to an 800% factor depending on the product and manufacturers tolerances. This is especially important in theatre because of all the incidental forces applied whilst doing the job as a whole - suppose you had a bar with a maximum load of 200kg, you have 150kg of "lights" already on it and you decide to add a 30kg moving light; because it's heavy you use a rope and someone pulling on the ground to lift it up.... you're almost certainly going to be well over the maximum load for the part because a) everyone forgets or underestimates the weight of cables/clamps and b) the dynamic load caused by someone on the ground pulling the rope that goes up over the bar can easily exceed 30kg weight of the object so you potentially have a problem. Conversely if the bar you're rigging from has an SWL of 200kg then you don't need to be too concerned about going (briefly) over-load because there's a safety factor built in. There was an incident at Ringling Brothers Circus a couple of years ago where a dozen aerialists hanging from a frame were dropped to the ground suffering life changing industries - after all the investigations the main factor was that someone had used a component rated at XXXXkg and assumed that was actually its SWL so didn't take in to account the extra forces applied by the moving performers nor the inevitable decline in the parts strength as it sustained wear and tear.

 

There's also added complexities that loads don't distribute evenly to the pick up points used so even if you have got a bar with 3x200kg SWL clamps on it that doesn't mean you could hang a 600kg object from the bar (unless it was multiple objects, evenly distributed and the bar itself was very strong) this is why there's lots of specialist engineering firms with expensive computer simulation software to calculate what really happens with the forces in play.

 

I don't want this to sound like I'm criticising you in any way - by admitting you were not sure and doing some research you are already more safe and more sensible than the majority of people, I just want to make sure that no one else reads this little bit of knowledge and misuses it somewhere else

Wow a brilliant post.

 

I'll reiterate the bit about loading during hoisting and how it is not understood by far too many people involved in the practice, a load of 30Kg suspended on a rope over the bar and back down will instantly impose a load of 60Kg. The friction applied while hoisting may increase that by another 30Kg quite easily, then depending on the smoothness of the bar and the type of rope and the jerking action there is easily another 30Kg. The jerking is generated by the stop/start action of hand over hand and the bumps in the shape (make up) of the rope. this is usually visible by watching how the existing lamps vibrate during hoisting.

 

It's easy to reach 400% of the weight or more of a load by running a rope over a fixed point, using a decent pully will usually reduce that to 300% but it is not possible to get down to anywhere near 200%.

 

As above don't forget to include ancilliaries in the load calculations, I have seen a 20ft ali bar loaded with 24 parcans suspended on 2 blue ropes, the rigger knew the weight of the fittings as 2.5lbs and worked on 60lbs total weight. He had not allowed for the bar, hook clamps, colour frames, barn doors, 15A plugs & sockets or 24 runs of 2.5mm² HO7 which all came from one end and were suspended from the wall several metres away. He had also not estimated the effect of the heat on the rope and one softened to the point it failed, the other rope failed as the bar swung down. Fortunatly the hall was empty during the rehearsal but the weight made it a bit of a struggle for 2 of us to lift it to one side.

Edited November 2, 2019 by sunray

[timsabre]

I'll reiterate the bit about loading during hoisting and how it is not understood by far too many people involved in the practice, a load of 30Kg suspended on a rope over the bar and back down will instantly impose a load of 60Kg.

 

Errr... I am not a rigger and I could be one of those people who don't understand it but is this actually correct? For a static hanging load isn't the load on the bar the same whether it is secured to the bar or on a rope over a pulley held from the ground. There will of course be dynamic forces from pulling and getting the load moving as you mentioned. But I don't think you immediately put 200% load on the bar. I am going away to draw some force diagrams.

 

 

Edit, ok I've thought about it more and you're right. If the load was equal to you in weight you'd be hanging from the rope and the force on the pulley would therefore be you + the load so 2x the load itself.

 

So your assertion about a lot of people not understanding is obviously true.

Edited November 2, 2019 by timsabre

[Jivemaster]

Sourcing the parts is trivial compared with being skilled, competent and practised in their safe use AND understanding the additional loads that will eventually be added to the assembly.

 

Start with an understanding of what the fixed building will support, then what the suspension fittings will support. Then add the weight of the suspension mechanism and all the hooks clamps cables lanterns etc and design a system that complies with the law of the land and the law of gravity and has a sufficient safety factor for safety.

[bradleypallister]

Bradley, Simply changing the word "they" to "we" would put you back within the accepted practice for the forum.

Thanks for the comment DrV, I'm a bit confused. I don't work for Kernow or connected with them in any way. Perhaps you could DM me with your comments, cheers

 

Sourcing the parts is trivial compared with being skilled, competent and practised in their safe use AND understanding the additional loads that will eventually be added to the assembly.

 

Start with an understanding of what the fixed building will support, then what the suspension fittings will support. Then add the weight of the suspension mechanism and all the hooks clamps cables lanterns etc and design a system that complies with the law of the land and the law of gravity and has a sufficient safety factor for safety.

 

Some great discussion and input in this thread. I think this is a good summary of the above

[DrV]

Bradley, Simply changing the word "they" to "we" would put you back within the accepted practice for the forum.

Thanks for the comment DrV, I'm a bit confused. I don't work for Kernow or connected with them in any way. Perhaps you could DM me with your comments, cheers

Apologies - I was confusing you with Robin Pallister who is one of their sales team.

[sunray]

I'll reiterate the bit about loading during hoisting and how it is not understood by far too many people involved in the practice, a load of 30Kg suspended on a rope over the bar and back down will instantly impose a load of 60Kg.

 

Errr... I am not a rigger and I could be one of those people who don't understand it but is this actually correct? For a static hanging load isn't the load on the bar the same whether it is secured to the bar or on a rope over a pulley held from the ground. There will of course be dynamic forces from pulling and getting the load moving as you mentioned. But I don't think you immediately put 200% load on the bar. I am going away to draw some force diagrams.

 

Edit, ok I've thought about it more and you're right. If the load was equal to you in weight you'd be hanging from the rope and the force on the pulley would therefore be you + the load so 2x the load itself.

 

So your assertion about a lot of people not understanding is obviously true.

It's not obvious is it Tim? Thanks for following it through.

 

One of my colleagues (who hangs lighting and sound kit) has read my post and didn't understand either, after I explained about 3 times I saw on his face that the penny dropped and his comment was: " ***k no... I mean yes"

 

So I'll try to clarify my earlier comments.

 

A static load of 30Kg suspended from a bar will exert 30Kg on the bar, regardless of the method of fixing it to the bar.

 

Passing a rope over a bar with a load of 30Kg on one end will need a load of 30Kg on the other end to balance it (just like a balance scale or see-saw), therefore both loads will be exerting their 30Kg or a total of 60Kg on the bar. It matters not how that 30Kg balance load is applied, it can be a 30Kg weight, a person pulling or even a static fixing to the floor below.

 

I hope that makes it easier to understand.

[timsabre]

The thing that bends my brain slightly is if you use a 2:1 purchase, so a pulley on the load as well, that reduces the loading on the bar as you are only putting half the down force on the rope. That seems totally counter-intuitive to me.

[James Remo]

It’s like the Grand Hyatt walkway collapse

, you need to think of all the forces you are placing on the system as a whole, as well as how those forces work as part of that system