[schooltechie]

Hi all,

Bit of background I left my school in 2007 and still help out with them on a voluntary basis. I recently discovered from the new site manager that the lighting rig hadn't been tested for a number of years and urged him to do this immediately. The result has came back and there are 2 points which need rectifying. The IWB's are suspended by some form of clamp around the bar then attached to the beams using wood bolts, the report has came back that these aren't adequate for supporting the load above people. The other issue is that the T60 upstage is hung off a bar which is suspended correctly, but the track is suspended with unrated chain and shackles.

They are getting a quote from stage electrics but as they are relatively simple tasks I feel that they can be done at a lesser cost easily. The T60 with threaded bar and appropriate clamps.
The beams are something which I'm unsure of, I have a lot of experience of using girder clamps off steel beams and using spansets and shackles. Spanies and shackles would be my normal route here but unsure of this in an install. Can anyone advise if this is acceptable or of another route suspending off wooden beams? If it does get done by the staff at the school I will be making sure that it has a load test and certifactes.

Or would this be something that is too complex and best leaving to the install companies. I'm happy in rock and roll and theatre but installs are a rarity for me.

Alex

[GridGirl]

To be honest, if you're asking then you shouldn't be thinking about doing it yourself. It might sound harsh, but when you have people underneath the gear, it's got to be done by someone who knows exactly what they're doing.

[bigclive]

So the IWB's are suspended by a clamp round the bar. (quite common) And secured onto wooden beams using "wood bolts" (Coach bolts?)

And what does your site manager suggest might be a better alternative? Without seeing the actual installation, it sounds pretty normal so far. Do you have a picture?

There's always a risk that as soon as you ask someone to assess the structural integrity of an installation that they will then cover themselves by suggesting it be upgraded to reduce their liability.

The track sounds dodgy though. Suspending track by chain can result in undesired swinging. It;s better mounted solidly.

[paulears]

Stage electrics have been using coach bolts on installations of IWBs and grid work for years, as have loads of other firms. Indeed, as Clive suggests - even if it turns out to be one of their own installs from years gone by, they'd probably like the job to upgrade safety. Who did the inspection? If it's a firm of engineers, then their report would also normally suggest the correct alternative?

This sounds like a job where you should step back and let other people do the work - if you do it, and stuff it up and it falls down - who gets blamed? You do!

[WiLL]

Don't mess about, bring in the experts. "wood bolts" could mean anything from M12 rated coach bolts and nylock nuts (perfectly acceptable in most cases) to coach screws, which are not. I've previously had jobs carried out by Unusual Rigging and Nippy Industries and been pleased with service and prices, so there's two places to start with.

[schooltechie]

After readings everyones comments, I will step back from this and just a advise the site manager on who to contact.

They are coach bolts or screws I apologise for my loose and incorrect terminology. The report from stage electrics (who did the inspection) simply says 'wood bolts'. The curtain from the chain I gathered from one of the older caretakers was chained by himself some 20 years ago as before he put it on it was held up by rope. I had told the previous site manager, head teacher and countless other people that this was wrong for sometime but it has only recently been acted upon by the school. The install was done by a local company originally not sure of the date but it was around 15-20 years ago.

As a matter of interest, if the coach bolts are unacceptable for some reason what would be the common route of installing IWB's off wooden beams?

Alex

[david.elsbury]

There's quite a difference between "coach bolts" and "coach screws". One is significantly less likely to pull out of a piece of wood......

David

[bigclive]

schooltechie, on 30 January 2012 - 11:59 PM, said:

As a matter of interest, if the coach bolts are unacceptable for some reason what would be the common route of installing IWB's off wooden beams?

It depends entirely on the locations. It would be up to the installer to assess the fixings required, but they could be direct bolting through wood or saddling the wood with unistrut and threaded rod.

As others have said, if you do anything to it yourself and it falls then you get the blame. Using an outside contractor removes that liability.

Coach screws have their place. For specific fixing applications I'd still consider large coach screws for mounting unistrut or other metalwork to thick wooden beams that were impractical to drill right through for the use of studding or bolts. Having worked on plenty of vintage theatre installations I've never seen a coach screw that had failed.

[indyld]

Just to add: I think that when we talk of using coach screws, most will be describing using them in a config that applies sheer force, rather than expecting the thread to take the load. With a decent plate, good wood and good fixings, they provide a solid anchor for the smaller loads in installs. Threads can be overtightened and instantly become useless though.

Again, it's understanding the engineering and kit, with suitable competence, blah....

This post has been edited by indyld: 31 January 2012 - 07:28 AM

[paulears]

Coach Bolt

Coach Screw
To be honest the coach bolt is rarely a problem because it's usually used horizontally, and then the load supported by a bracket that is U shaped, below the timber beam. The coach screw, on the other hand can be used horizontally, in a similar way, but can be used in ways where the load is on, or close to the axis of the screw - meaning pulling out can happen. Big name installers used this technique in two local small installs. Victorian buildings, long old fashioned school halls, taken over by theatre users. The main roof timbers go up to the apex at 45 degrees, and in one installation, U shaped saddles went over the tube, and were coach screwed into the timbers, so the load is at 45 degrees to the thread axis. In the other one, brackets were coach screwed to the highest horizontal timbers, and then studs dropped to support the centre spans. This seems to be quite common. I've seen the same technique in a number of installs - although I can't be certain from ground level that they are coach screws, but they certainly look like them?

[Andrew Edwards]

Whilst I have nothing against Stage Electrics*, might it not be prudent to get a few other quotes.
Indeed, I would have thought that the school policy would have been at least 3 anyway.

Tell the companies that your are getting several quotes and you will usually get an honest and fair assessment of the work.

*There is not a single area of our venue that does not have any evidence of their work. Stickers everywhere...

[DSA]

An alternative fixing detail could possibly see a bolt (or studding) passing vertically through the member, with an appropriately sized washer between the bolt head/nut and the top face of the timber beam. The washer size would be a critical consideration in such a design, and could well be quite large.

David

[Maddison]

schooltechie, on 30 January 2012 - 11:59 PM, said:

As a matter of interest, if the coach bolts are unacceptable for some reason what would be the common route of installing IWB's off wooden beams?

There are many options available. I noticed that Doughty have a special which they could adapt if you wished to avoid the through the wood approach.



Doughty Joist Bracket

[WiLL]

Maddison, on 01 February 2012 - 10:09 AM, said:

schooltechie, on 30 January 2012 - 11:59 PM, said:

As a matter of interest, if the coach bolts are unacceptable for some reason what would be the common route of installing IWB's off wooden beams?

There are many options available. I noticed that Doughty have a special which they could adapt if you wished to avoid the through the wood approach.



Doughty Joist Bracket

I like the look of that as it doesn't involve making a hole in the joist. But I suppose it makes up for it with being one ugly looking beast.

[rossmck]

I've seen 'professional' installations (in small venues) where coach screws were screwed through a ceiling and into a joist (vertically) relying on the pull-out strength of two screws to hold a bracket in place which the bar was suspended from... these have been changed to brackets up and over the joist, with threaded rods and locking nuts... and no longer move when you put a load on the bar

Anyway, personally from the above the Doughty Joist Bracket looks the most appropriate but it's hard to tell without seeing your space. Best get Stage Electrics and a couple of others to give some quotes they'll be better placed to give advice than any of us can on a forum...

I have done this sort of work myself, but would always get someone in afterwards to test and sign off ... as others have said, if you do it, then you're responsible if it does go wrong.