Lighting Grid Design

[Barreller]

Sorry if there is s thread on this one but I couldn't find it. We are in the process of converting a building into a studio theatre. The idea is to have a free standing lighting grid built out of trussing. Fixing to the floor is not a problem but walls and ceiling might be. Does anybody know who we can turn to for design. Financials might mean that we source second hand so we need a designer.

[Dave m]

Surely by "free standing" it relies on the floor?

A basic multi legged "table" structure can support a reasonable amount and probably needs no bracing to the walls or ceiling.If you felt safer, a simple overhang that is close to the walls would prevent it tipping

[paulears]

It's easy to use scaff outriggers with wall plates and non-damaging surfaces to prevent any lateral movement if you think this important - but I doubt you'd even need to fix to the floor - the weight of a ground supported grid tends to be perfectly solid for most applications, and also 'alterable' if you need cross positions in different places. A pile of truss parts and you can be creative - maybe even incorporating the truss into the set - hanging drapes from it and making it a feature?

[Barreller]

Thanks Paul. That is the intention. I need help with the design.

 

The space is 6m30 by 5m90 and 3m60 height.

 

It's the loading I need to know about. Obviously I can use a manufacturer but as ever the budget might not stretch to new.

 

We might brace off walls but I don't want to fix to them. It's basically a big table!! I can fix to the floor.

[ImagineerTom]

The problem with second hand truss is that it’s an unknown - a tiny dent or crack in a key point could halve it’s structural properties; After market pins / bolts / grenades change the rating of connection points. Any structural engineer could do the theoretical sums to calculate loadings on second hand truss but would end up giving you something with so many caveats on it that it would be worthless because unless they can inspect (and possibly x-ray) the second hand truss in detail they can’t make absolute commitments about how strong it will be. When buying new truss you’re really paying for the evidence chain that ensures the right grade of Ali was bought to make the tubes, the welds were done with the correct grade materials and no damaged components have snuck in to the batch.

 

You may find a second hand truss supplier who is also prepared to “design check” your project if you buy the truss from them and provide some sort of certification and loading recommendations but that will be more expensive than buying truss yourself and unless they are a big well established company their certification would be worthless.

 

Getting someone else to take legal responsibility for your truss (which is what a design commission partially involves) gets expensive. You will probably find it quicker, easier and only marginally more expensive overall to juggle the budget to get some new truss with certification than to try going down the “cheaper” route.

Edited October 11, 2020 by ImagineerTom

[paulears]

What I do know is that I'd buy from a supplier who offers a warranty (which is probably a bit pointless for what will be static truss, and lightly loaded compared top capacity) at a price you can afford.

 

Second hand is perfectly possible if the same criteria apply - branded truss with a loading far below what it's capable of. If the venue intend to get the support kit inspected regularly - annual checks seem quite common in schools, colleges, universities and smaller theatres - then you make sure that visually, you, as the user cannot see anything damaged, cracked or bent - and then rather than wait a year, get the first rig checked before you use it. The usual theatrical engineering firms will happily do this and as you're not going to constantly fiddling with it and throwing it on trucks, that would work for me, and the kinds of insurance companies I dealt with.

 

If you buy 4 chord truss like Global Truss F34 cost wise new, it's more expensive than 3 chord truss like F33, but more flexible if you want to make different shapes. 3 chord truss has two versions of some corner/jpint sections to cope with apex up or apex down lengths which (as I discovered) does confused a tad - but 3 chord truss is something like £100, vs £150 for the same length. If you buy carefully your possibilities are OK. In college, we a pile of 3 chord truss and most of the things we did with it stood on 4, 6 or occasionally 8 legs, each one two sections of 2m, sitting on a baseplate. We added to it a couple of years after purchase - an ebay purchase, through an intermediary as we were not allowed to buy direct from ebay sellers. I looked at it and was happy with the condition. This would have been probably around April. In the summer the engineering firm came in and examined it and looked at the new bits we'd got in the store. They spotted a dodgy weld - probably just a bit fill-light and repaired it and included the new stuff in the inspection report which kept the powers at be happy. We used the stuff for nine years and it was never fixed down, always freestanding and the top just lightly braced - which wasn't actually needed, but did stop the top wobble when movers all moved at the same time.

[Junior8]

Unless you are able to source used suspension equipment of any kind that comes with a warranty that is worth the paper it is written on forget it. If you can't afford to the job properly don't do it at all. That being said I think you have made things much more difficult for yourself by rejecting wall mounting. A floor standing system might seem easy - and for a temporary fit-up the only solution - but you could well find that the presence of legs makes other things like exits tricky.

 

Faced with a small space like this my first impulse would be for standard wall bars not truss but you may have good reasons for your preference.

 

But if you could wall mount if you were to use Doughty 300mm stand-offs and 2m ali barrel each unit would be well within the amount an individual sponsor might well fund for their name on a plaque by it and it would be new. Just a thought

[GR1]

Your profile has you located in Somerset so I think you should look at the PLASA website for a level 3 qualified rigger in your area then explain your situation and ask them if they would be prepared to give you the benefit of their advice for the price of a very [very] nice lunch. In these days of Covid and with almost no rigging work you might get lucky. You will need to know exactly what you want to put on the truss because no one can reasonably answer what if questions.They will be able to explain the legal situation as well as the operational one. Once you have real world advice you can decide how to progress. I book riggers for the events I need kit hanging and without exception they understand the risks of their working environment and the implications for the other crew and the audience and always give me good advice.That is what I would do. At this stage I would avoid potential suppliers because they will only want to sell to you and you don't know what you want yet. Edited October 11, 2020 by GR1

[Jivemaster]

If the budget doesn't stretch to NEW then can you afford the professional fees for design and initial inspection. Every year recently there has been some truss damaged in a collapse, you really DON'T want to buy that bent stuff even if it's cheap.

[paulears]

Who suggested using old or bent truss? We're getting carried away here, making huge assumptions. Nobody as far as I can see suggested anything about buying old damaged truss. I doubt anyone here has anything better than the Mk1 eyeball for determining truss condition. See a dent, or a crack, or signs of repairs and you don't use it? Even riggers don't carry X-Ray machines do they?

[Ynot]

Yup - I reckon some posters are over-egging the pudding to an extent.

 

Any truss that's seen a little life on the road either on a tour or from a hire company and sold off after is going to be second hand/used be that used for a month or three or a year+. Whether that truss is going to be sub-standard or not depends entirely on how it's been treated by the crew in question.

 

Now - any truss in a hire company's stock is effectively going to be 'used' and the proberty of such is not really going to be something that you'll know if you're hiring. Some of the bigger boys MAY do a more detailed check of kit as it comes back in but I doubt the smaller outfits would. But does that preclude them next time you want to hire in? I seriously doubt it.

 

So the general advice I'd give for anyone is make sure that YOU give any truss you buy a good looking over BEFORE you part with cash.

 

For the OP here, who wants a floor-bases setup at 12 high (NOT that tall in the grand scheme) with relatively minimal planned loads is to just look at specs for whatever truss he's looking at.

I've used tri-truss over a 5m span with no problem (following guidance) and I'm pretty sure I've been on load-ins where box truss with 7+ metre spans have been fine. DON'T quote me on those as I'm not qualified for chapter & verse, but it does sound like we're building a mountain for this guy to climb where it's really not necessary.

[dje]

Your profile has you located in Somerset so I think you should look at the PLASA website for a level 3 qualified rigger in your area then explain your situation and ask them if they would be prepared to give you the benefit of their advice for the price of a very [very] nice lunch.

 

Whilst I understand your principle, I think we should remember that there is no sort of structural design criteria in the Level 3 (or indeed, Level 2) assessments. Now, that's not to say that somebody who has an NRC Level 3 shouldn't be capable of designing a range of truss structures, I'm sure that many, if not most, are. But no more inherently so than a Level 2, and no more inherently so than a suitably experienced person without any NRC qualification. From a CDM perspective, selecting suitably qualified contractors is important and neither NRC certification is really the 'correct' proof of suitability, from a design perspective.

 

For the most part, from a design, legislative and possibly insurance standpoint, this'd be better with an engineer than with a rigger.

 

One of the big problems with used truss is getting hold of it. Seriously! Most companies hold onto their truss until there really is a reason to get rid of it, ie damage or fatigue. Where 'tech' - like sound, lighting or video equipment - will become obsolete as newer, lighter, faster, brighter, louder products replace them; things like truss, staging and cable tend to remain in hire stock much longer and are retired only once they are either broken (and beyond fixing being economical), worn out, or just not needed anymore. (The latter being seldom applicable to truss, except things like PAR can pre-rig).

With the main development in truss being the cost of it (going down), if you can even find all the bits you need used, I'd be surprised if the cost of used truss + inspections etc is actually any cheaper than an all-new solution.

 

As for Somerset... Stage Electrics or Enlightened Lighting would certainly be able to handle something like this.

Edited October 12, 2020 by dje

[kerry davies]

Ah well, time I got shot down in flames again.

The OP has jumped to the use of trussing, presumably meaning aluminium show trussing, as the solution to their desired outcome. This is not necessarily how a structural engineer would approach the project. Personally I used to start from the very basics of "what am I hanging" before "where" and so on and so forth. Scaff pipe would take up a lot less space and headroom and can be combined with ladder rack etc and in fact is how aluminium show truss came to be created. For a semi-permanent solution it is not necessarily the optimal answer to use kit designed as temporary and portable.

 

Advice? Get an experienced structural engineer to give that advice, none of us can see the environment and we don't have enough detail on what you wish to hang. Think very carefully about what you do hang and don't get over-ambitious. In a room that size umpteen moving heads are not going to be best, the lounge in my council flat is as long as this space.

 

E2A Just an opinion here but hiring in a structural engineer also helps out with passing the buck on insurance and, in a studio space presumably with punters/amateur actors under the framework, that would be something to think about.

Edited October 12, 2020 by kerry davies

[ImagineerTom]

Yeah I have to fight back here (and with apologies to the OP) but the very fact the OP has had to ask this sort of question on a public forum means by definition they would not meet the legal requirements of a competent person for legal purposes when it comes to assessing and testing any second hand truss they purchase. Furthermore because this is a studio theatre and the grid goes wall to wall that means it's over the public's head and (since they're talking about fixing it to the building) it's a permanent installation which brings it under the auspices of building control regs and fire department safety standards. This rig not only has to be structurally sound within itself from a show point of view but also meet lots of other requirements about durability in an incident situation (since it runs over all the doorways, is it designed & certified so that in 20mins of fire it cannot drop down and block the fire exits?) which is a whole other can of worms. Normally all that complicated stuff can be abated by saying "here's a brand new rig, here's the certificates for it and here's the big reputable company who've designed and inspected it all whilst making sure it complies with the appropriate regulations" and that will make almost all of those problems go away. As soon as you say "we bought a load of second hand truss, couldn't afford to get it formally inspected and got a third party company we found on the internet to design it without testing" the hackles of all those safety people will go up and you will have infinitely more hoops to jump through.

 

To the OP - is a truss rig REALLY the right solution; would not an old-school checkerboard of scaff bar's hung directly from roof joists be a more practical solution? Certainly it would be a lot cheaper than trussing - fag packet calculations you'd need about 50m of scaff to build a suspended grid whereas you're looking at 40m of truss plus corners & footings for what you are planning - plus this sort of suspended grid design is easier to source, easier to inspect and frees up lots more usable floorspace whilst giving you lots more ready-made-point in the sky?

 

t

[Brian]

Important first questions for anything ground supported...what's the 'ground' made of and will it take (relatively) point source loads?