Scaffolding feet

[J Pearce]

Not that that is recommended by litestructures... Using the correct 4 leg adaptor (affectionately known as udders) is however.

[kitlane]

Are you using four legs a deck? You could save on legs by only doing one deck on 4 legs, and the rest on 2 legs, If you go down this route, make sure you double bolt all the decks.

 

At the risk of opening a can of worms... I tell my students to check with the manufacturers instructions before doing this. With many brands of deck you are instructed to use special adapters to do this. They spread the load of adjacent decks directly to the leg rather than relying on the bolts which would be under a shear force

 

EDIT: Well that teaches me for starting a reply and leaving it for half an hour before finishing and posting. I'd like to take the credit for Jon's response but I think he probably knew that before I ever mentioned it to him.

[AndyJones]

Bolts, when used to fasten deck together generally aren't meant to be used in shear force to carry loads. They are designed to attach by clamping the deck together (with nut, bolt and washers) to enable the friction between the two decks to transmit the loads. Unless you are are lifting significant loads ( a car for example?) Then having four bolts between two bits of deck will be more than sufficient. I have used udders when the loads are increased.

[Ynot]

Are you using four legs a deck? You could save on legs by only doing one deck on 4 legs, and the rest on 2 legs, If you go down this route, make sure you double bolt all the decks.

No,. we're doing precisely what you suggest and always have done with these decks. For larger decking options, we have indeed hired in the LS 'udders' as required.

[kitlane]

Oh well. In for a penny, in for a pound.

 

When holding two things together with bolts, the efficacy of the connection is down to the friction between the mating surfaces. My experience with decks is that unless they are brand new there will be bits of frame that are bent, the ply top is slightly overhanging, someone has painted it (thereby altering the coefficient of friction), there is some velcro stuck to the face etc. etc. All these things could reduce the contact area of the mating surfaces.

 

How tight do the bolts need to be? Too tight and you might start distorting the frame. Not tight enough and there is insufficient friction. I couldn't tell you off the top of my head.

 

I'm not saying I have never bolted decks together to reduce the leg count, and I'm not saying I wouldn't do it again. But I wouldn't advise someone to do it without knowing a lot more about their application, the state of their equipment and the confidence they have some understanding of the mechanics involved. I might point them here.

[Ynot]

Hmmmm... ©

 

I can't help feeling this has gone off at a tangent, and not one that's really contributing to the original discussion...

 

For the majority of applications in theatre, the load on such things as Litedeck/steeldeck etc are unlikely to be huge, and as such won't be putting undue shear force on the bolts. And let's face it to shear off one bolt, let alone 4, would take a pretty large downward force (without going into the base mechanics - all due respect to kit's link).

 

In circumstances where larger loads (eg car launch/display) are anticipated, then of course I'd recommend all 4 legs be used and maybe even then also all 4 bolts securing the deck. And if there's a question mark, I'll always err on the side of safety. But for general sling it up and bolt together, I'd be more than happy trusting to just bolting on the sections as described.

[kerry davies]

Don't agree with that last post sorry Tony, have to go with Kit's post.

 

Above 950 mm, Litedeck state you must use leg-frames, with which you can use "leg-tops" to allow "walk-throughs under stages and omit legs from intermediate deck units. AFIK they do not allow in the MI's for omitting legs on non leg-framed structures.

 

FWIW the US Steeldeck site has this to say about tightening things up (I hid from the mentions of staging in the impact-driver topic); Note: Bolts and hand knobs should be tightened firmly, NOT forced. The tools they show on their MI's are a podger and a manual torque wrench. So if steel is not to be "forced" I would take a belt and braces approach to aluminium.

 

OK, we sometimes do it, but every time we do we risk going against MI's which leaves us pretty lonely in arguing that it is acceptable practice, which I think is Kit's point. As far as using scaff couplers as "spacers" is concerned I would also be reluctant as they aren't designed to take those kinds of compression loads with no tube on one side of them.

[Giles Favell]

Under no circumstances should decks be held up using the 'joining' bolts. They are there simply to prevent decks from moving apart - and themselves should never be over-tightened.

In most instances, the deck ply over-sails the truss member by 1mm or so (by design) - and so if the bolts are 'tightened', they will pull the side trusses together (which they are not intended to do) thereby loosening the grip of the deck screws, straining the truss, and often (through over-enthusiasm) crushing the top chord of the truss.

 

You can wreck a deck this way, or severely weaken it.

 

As everyone here really knows - it's bodging - and it shouldn't be done - so don't do it. It won't pass inspection from anyone who knows what they're looking at, and there's the hardware easily available if you want to 2-1 or 4-1 with legs without compromising your loading.

 

Decks MUST be supported from underneath - not in shear from the side truss section.

 

 

 

:) Giles

[Ynot]

OK - I'm going to bite on this one, because I'm still a little sceptical about the whole 'Thou shalt not put decking under shear risk...' theory.

 

So - give me some figures, some science, some evidence to support why we should NEVER just support decking using the support of joining bolts.

 

Because over the years I've seen, used and built structures which use supporting members doing just that.

Timber joists bolted to a brick wall, with spans of decking or timber & plywood frames. I've seen whole stages built at outdoor events built EXACTLY in the way described above, with no problems in evidence.

 

Has there EVER been a documented incident where any support bolt (let alone FOUR) has sheared due to lack of additional support?

 

Because I'm sorry - despite not being a mechanical or structural engineer I do feel I have enough common sense and practical experience built up over 30 years to be able to assess whether a structure I build is capable of supporting the (comparatively small) loads I'm ever likely to exert on them. And before anyone spouts anything of the ilk "Well you can expect to explain that to a judge in the future then..." I seriously doubt it! I just don't build things that are likely to fail, and in fact I'm more often known for OVER-engineering for a higher safety factor!

 

Now having had a quick Google around, I couldn't find any specific MI's on the Litestructures web site (though I'm sure there must be something somewhere).

Anyone have a link?

 

 

[Giles Favell]

Well..... I'm not in a position to speak for Lite structures, but I have designed well known decks for a living, and know why they are designed the way they are, and with the holes and bolts they have, at what spacing, and what reinforcing they have, and how we intended them to be used........

 

:D

[kerry davies]

Giles is right Tony. He is pretty much an expert and the Steeldeck parts list states;

 

"DESCRIPTION: M10 x 60mm (Grade 8.8) bolts with wing nut. Used for joining decks through pre-drilled holes along all edges of standard decks. Finish: zinc plated. TECHNICAL SPECIFICATIONS: LOAD CAPACITY N/A"

Note that N/A! Note that wingnut, not a nut and bolt!

 

I must now "come clean" and state that the practice might be our own fault for creating welded leg-tops to use with Steeldeck on Kwikform back in the eighties. It "looked" like we were simply leaving legs out and doing what you suggest but it certainly was not that.

 

Forget Litestructures, if steel can't take it then ali definitely won't. I must say I am surprised that Litedeck have no downloads on their site and will ask them why not next time I see the guys. Mind you the Steeldeck info is only on the US website AFAIK.

[Ynot]

Hmmm...

All due respects to recent posts, but I remain unconvinced at this point with regard to the specific situations in which we use Litedeck regularly at my (small) venue.

 

For clarity, that is usually a single run of 4' wide deck across the back wall of the stage, (32' max), on 6' 6" legs (with diagonal braces where appropriate).

Occasionally there's a 4 x 2' section added as a dog-leg at one end to accommodate the front end of the drum kit (so VERY limited weight load there).

 

In addition, the decking is secured to the permanent 4 x 2" timber batten by coach bolt with washers through the decking main holes - usually 2 per deck section to add stability to the structure.

 

Now, to my eye, and as I've said I've no qualification other than experience and a solid dose of common sense, this is perfectly suitable for our needs when using as a band rail and even more so if it just serves as a backing or walkway for occasional functional set pieces (eg during panto). Extra legs for each deck in this case is, I feel, adding redundancy.

 

Now, as I said in an earlier post, where we bring in hired extra deck and add a second 2' or 4' run across the front of the standard rail, we've hired in the udders as someone calls them to link the legs deck to deck.

 

Note that I am NOT talking about building full stages with decking, and there is no likelihood of dynamic loads (such as dance routines) being executed on the 4' single run of top-deck. If I were to design and build a full stage (which I doubt is likely) I would of course reassess the method, and probably modify my thoughts accordingly.

 

But what I actually asked for yesterday was some MI documentation which gives chapter and verse about how to erect Litedeck. AND I asked for evidence that the risk of shear is in fact real under normal loading - and whether there have been incidents where just side-bolting have resulted in shear failure.

 

Kerry, your quote doesn't seem to cover anything that I'm questioning. Firstly the suggestion is, I believe, that therisk associated here is shear force on the bolts used - so the compariosn between Steel and Ali is false - steel being that much harder is, I suspect, MORE likely to cause shearing than ali, which logic tells me would more likely distort the deck hole slightly before chopping off a bolt.

 

And the quote you gave only refers to the bolting together - no mention of legs at all...

 

Forgive me for dragging out the discussion, but I'm very interested to hear more from those who have a reasonable point to offer.

As with all things, I'm willing to listen and even be persuaded that I need to change my practices, but I'm seldom a pushover - you may need to work hard to convince...!

[dsharp7th]

I had approval from litestructures hq for using 2 legs where 4 decks joined (opposing corners), or one leg where two joined along an edge, in order that 2 screwjacks could be used with the bases just fitting when turned to 45° to the decks. This was subject to ISO bolts being used.

 

This was for litedeck stage on grass and I have since switched to layher.

[kitlane]

 

Kerry, your quote doesn't seem to cover anything that I'm questioning. Firstly the suggestion is, I believe, that therisk associated here is shear force on the bolts used - so the compariosn between Steel and Ali is false - steel being that much harder is, I suspect, MORE likely to cause shearing than ali, which logic tells me would more likely distort the deck hole slightly before chopping off a bolt.

 

 

I may be being thick but I don't follow this part of the argument. The shear force is applied to the bolt which is always going to be steel. It doesn't matter whether the deck is made of steel, ali or rice pudding, the shear load on the bolt will be the same. Unless you mean that the ali surrounding the bolt hole will deform more easily than the steel, thereby somehow absorbing the load?!??!?!?!? This doesn't sound desirable. If the bolt hole is distorting then clearly you need more legs or to use 'udders'

[Giles Favell]

Ah well.....

 

 

 

As I said, I can't speak for Lite Structures - as for Steeldeck, informally, I can - and if your interested, I'll try to fill in a few gaps, but if your not - feel free to ignore it! :D

 

 

The problem isn't as simple as 'shear on the bolts', and neither is the problem only catastrophic failure, as you infer. Other issues include very real unseen damage and weakening of the deck, not to mention hazards associated with percieved strength of the stage (which it absolutely can't live up to) and the hazards of fitting up and dismantling the same.

 

The first problem is that in tightening the bolts you are closing the 2mm gap, and distorting the truss (which DOES weaken it - temporarily if it is not overdone, but permenantly if overdone). This also trashes the adjacent deck fixing screws - which isn't good.

 

The holes in the deck are 12mm dia. and the bolts are 10mm dia. which mean that you do have to tighten the bolts (if you are not using legs) if you are to avoid the second deck sinking.

 

The holes in the top chord of the truss are reinforced with a plate tack welded at the back to help preserve the thin ERW section, but they are not bushed - so there is a very real limit to the amount of compression they will stand before the section starts crushing (at which point all bets are off on the usefulness of the deck)

 

And very importantly:

 

When you pull this trick, you double the load on the side truss on the adjacent deck, which is already working hard (in heavy load scenarios) and can take it way past acceptable parameters. WHAT IS WORSE, and this applies to lower load-case scenarios, is that you are transferring this load at two or four fixed points along this truss (in the middle of a drilling through the chord - by definition the weakest point) instead of a UDL across the top face of the chord, as designed. In fact you are abusing the chord most cruelly, and hoping you'll get away with it because you're not putting much load on it...... the fact it might not take so very much load in this fashion hasn't really occured to you, and you certainly can't quantify it!

 

As to putting the bolts in shear, you'll be lucky to get them into a text-book shear scenario without bushing the holes and packers between decks, as they will also be susceptable to stretching and bending under these loads (we've seen them...)

 

 

I hope this in informative even though it's not Lite Structures.