Truss I-beam runner/wheels

[david.elsbury]

http://i66.tinypic.com/rjo3uh.jpg

I have a venue that we hang LED wall in. There are two vertical I beams that sit forwards of the beam in the roof where the motor chains attach. Therefore the horizontal truss when lifted runs up the front of the vertical beams. I mitigated this last time by attaching carpet to the truss but would prefer something like the above with wheels that clamps to the truss.

http://i64.tinypic.com/aervxe.png

 

Can anyone suggest an off the shelf product?

 

Thanks

David

[gyro_gearloose]

A castor on a half coupler, one set per side positioned so that it runs up the middle of the vertical beam? Since your truss is only being lifted vertically I don’t think you’ll need to worry about lateral movement, so you shouldn’t need to have as many wheels as you’ve suggested. If sideways movement is a concern, then two more wheels, one per side, mounted such that each runs up the inner edge of each I-beam should stop any sideways movement.

[Seano]

Can anyone suggest an off the shelf product?

 

I don't think you'll find one. The nearest thing that comes to my mind is a beam trolley, the wheels are flanged like a railway locomotive so exactly what you're after but they're designed to be used in tension rather than compression so some kind of modification would be needed.*

 

If there's any engineering required at all though, your efforts would probably be better directed towards moving your rigging points forward to put them over the truss where you want to hang it. You're almost certainly using those beam clamps outside their spec as it is (most of the manufacturers say you should be loading them perpendicular to the beam), so it would be a bonus to replace them with something else. Any solution that moves the truss further forward is just exacerbating the situation really.

 

Is the beam slingable? Is there another one further towards FoH? If so, seems like a no-brainer to put a bridle in. Choke on the downstage side of the beam with a suitable sling, use the excess as your short leg, brail forward with a 6mm steel terminated in a Reutlinger could be the way to go.

 

If it's a regular gig it might be nicer to get a bracket fabbed up and install it permanently, could be as simple as a wee bit of steel with a pad eye and a few Lindapters.

 

* - Oh! Unless you put a beam trolley on the upstage side of the column, cantilever a couple of tubes over the top chords and off the back of the truss with a third to make a 'hoop' around the column and pull upstage against the trolley. That'd work I think, bit Heath Robinson though, putting the rigging points in the right place still much the better answer I think.

[ontoprigger]

Hi David

As others have said something off the shelf is going to be hard to find, but there are a few products that could be adapted, what are the dimensions of the beam?

 

As Seano pointed out, most beam clamps are not to be used on a sloping beam, I know Showquip have some that are made for that purpose, they have a bunch at the Civic for the front of house points. you may also find they have something that will help push the points further forward away from the columns.

 

I am in Auckland for a week for a bump out, from tomorrow if its something you want someone to have a look at there may be something I can do while I'm there, let me know.

[kerry davies]

It looks as if you are re-inventing the cradle that carries horizontal truss up on self climbing stage roofs and as such you might be better using the whole depth of the RSJ rather than the flange. That way you would get two dimensional security and avoid the screen moving side to side or back and forth.

[T*ny]

Clamp a block of PTFE to the truss and let that run up the RSJ?

[david.elsbury]

Thanks all for the replies :)

 

A castor on a half coupler, one set per side positioned so that it runs up the middle of the vertical beam? Since your truss is only being lifted vertically I don’t think you’ll need to worry about lateral movement, so you shouldn’t need to have as many wheels as you’ve suggested. If sideways movement is a concern, then two more wheels, one per side, mounted such that each runs up the inner edge of each I-beam should stop any sideways movement.

Point taken - yes inside edge might be the way to go? I am a little concerned about sideways slip and the truss smacking against the beam, wouldn't do the LED wall any good.

 

The nearest thing that comes to my mind is a beam trolley, the wheels are flanged like a railway locomotive so exactly what you're after but they're designed to be used in tension rather than compression so some kind of modification would be needed.*

Beam Trolley! That's it :)

If there's any engineering required at all though, your efforts would probably be better directed towards moving your rigging points forward to put them over the truss where you want to hang it. You're almost certainly using those beam clamps outside their spec as it is (most of the manufacturers say you should be loading them perpendicular to the beam), so it would be a bonus to replace them with something else. Any solution that moves the truss further forward is just exacerbating the situation really.

 

Is the beam slingable? Is there another one further towards FoH? If so, seems like a no-brainer to put a bridle in. Choke on the downstage side of the beam with a suitable sling, use the excess as your short leg, brail forward with a 6mm steel terminated in a Reutlinger could be the way to go.

 

If it's a regular gig it might be nicer to get a bracket fabbed up and install it permanently, could be as simple as a wee bit of steel with a pad eye and a few Lindapters.

Not too regular at this stage, but who knows - new venue and all that so fingers crossed. Slinging would work but would be concerned about slippage. But your point is noted re the beam clamps. See pic below, not a great snap sorry but the next beam 'downstage' is quite a ways away.

http://i65.tinypic.com/2ez5kky.jpg

 

Hi David

As others have said something off the shelf is going to be hard to find, but there are a few products that could be adapted, what are the dimensions of the beam?

 

As Seano pointed out, most beam clamps are not to be used on a sloping beam, I know Showquip have some that are made for that purpose, they have a bunch at the Civic for the front of house points. you may also find they have something that will help push the points further forward away from the columns.

 

I am in Auckland for a week for a bump out, from tomorrow if its something you want someone to have a look at there may be something I can do while I'm there, let me know.

Thanks for the offer - it's not something I feel the need to drag you into look at - thanks though! - but I might give Showquip a call and have a chat. I don't have exact dimensions, maybe 200mm square round figure?

 

It looks as if you are re-inventing the cradle that carries horizontal truss up on self climbing stage roofs and as such you might be better using the whole depth of the RSJ rather than the flange. That way you would get two dimensional security and avoid the screen moving side to side or back and forth.

Thanks - might see if there is a way to adapt something along those lines.

 

Clamp a block of PTFE to the truss and let that run up the RSJ?

Wouldn't that affect the paint finish on the RSJ though? Slick (ha!) idea though.

 

Thanks all

David

[Seano]

Beam Trolley! That's it :)

 

It wasn't an entirely serious suggestion though, just a bit of a Heath Robinson doodle really. I mean it could well work, but it's a daft idea. ;)

 

See pic below, not a great snap sorry but the next beam 'downstage' is quite a ways away.

 

The pic is clear enough. It'd be a no-brainer for me: don't try to 'run' the truss up the side of the vertical beam, move the points forward. The quick, cheap, easy way to do that with a temporary installation is to bridle between roof arches. The slope isn't steep enough that a basket will slip, a choked Spanset or Gacflex certainly won't slip, but if you want a bit of extra reassurance that it wont, move your point off a wee bit to butt up against the onstage side of the purlin. If you use a 4m (2m EWL) sling choked, it looks to me like the sling itself will be long enough for the short leg of the bridle.

 

The long leg would carry a very small percentage of the load and not be far off horizontal, so it wants to be lightweight really - as above, I'd suggest you use a 6mm steel (maybe even a 4mm steel) and a Reutlinger, put the Reutlinger at apex of the shackle (as opposed to over at the far beam) to make it easy to adjust (and re-adjust if necessary when the truss is floating). If the leg is a heavier steel, and especially if you try to adjust it's length with a STAC, there will probably never be enough tension to pull the 'belly' out of it.

 

Napkin-cad sketch to follow, possibly...

[Seano]

Ok, blurry photos of napkin-cad sketches...

 

I've guesstimated some dimensions, all in mm. Going to call the beam 450mm x 190mm (would be a fairly common size over here), assume you're using a 300mm truss, and guess the roof arches are 5095mm apart.

(Actually I guessed a 5m span for the bridle, but with a choke on one beam and a basket on the other that would put the beams an additional half a beam's width apart.)

 

So, napkin-cad sketch number 1:

 

http://www.deepsoup.f2s.com/BR/DEbridle1.jpg

 

The point wants to be 280mm forward of the edge of the beam for the truss to just clear the column (300/2 + 450/2 - 190/2), lets round that up to 300.

 

Napkin-cad sketch number 2:

 

http://www.deepsoup.f2s.com/BR/DEbridle2.jpg

 

At these beam sizes I was wrong about a 2m EWL sling choked being a nice length for the short leg of the bridle. 2m - the perimeter of the beam = 720mm, just a wee bit short. Lets use a master link for the apex and chuck another in the short leg to give about 1m. We're looking for around about a 90 degree included angle.

 

Napkin-cad sketch number 3:

 

http://www.deepsoup.f2s.com/BR/DEbridle3.jpg

 

A few sums. Starting with the length of the short leg and the horizontal distance to the point, Pythagoras theorem to fill in the other dimensions, bit of trig to get the angles.

 

Load on the long leg is pretty much 100% of the point load.

 

Load on the short leg about 30% of the point load (sin(17.5)/sin(92.9)=0.30 ), my wild guess is that those points are around 300kg, so that'd be 90kg. No problem with a Reutlinger on a 6mm steel.

[Dave m]

Given the discussion I think I don't understand a fundamental risk but can't you just fit a pair of girder clamps /gravlocks and have two short steel bars at more or less right angles to the rsj's ? Is the load too great for that?

[Seano]

Is the load too great for that?

 

Probably not, but the load isn't trivial so personally I think I'd want the go ahead from a structural engineer for that.

[david.elsbury]

I calculated at about 400kg per point all up so I wouldn’t be in a hurry to mess around with gravloks and clamps to try and pull the beam forwards.

Thabks Seano- will look closer at it but I see what you mean- nice solution

[empyfree]

Seano, your Napkin cad could put many an AutoCad user to shame!