Truss rigging at an angle

[yyy898]

Hi,

I have a truss which I need to rig a an angle,

I have the total weight (UDL) and the height, angle, length, ... of the truss.

 

What is the formula to calculate what the load in each rigging point will be ?

http://i66.tinypic.com/4h41hx.png

 

[timsabre]

er... it will be the same as if the truss was horizontal. As long as the points are hanging vertically.

[Shez]

What I suspect may be of more concern is how you attach to the truss at an angle - it may not be the same hardware and techniques you'd use when rigging horizontally. But then I'm not a rigger ;)

[Seano]

er... it will be the same as if the truss was horizontal. As long as the points are hanging vertically.

 

Near enough, as long as the truss is long compared to it's depth and the depth of the fixtures hanging off it, and the angle is not so steep.

Otherwise there will be a slight (or not so slight) shift in weight on to the higher point, as the CoG of the whole thing moves in that direction when it's tilted. You can re-equalise this to some extent by biasing the position of the pick-ups to have a slightly longer cantilever at the lower end.

 

it may not be the same hardware and techniques you'd use when rigging horizontally

 

Probably will be, though not all hard fixings are suitable. There are many ways to wrap a sling. Requires a bit of care though, obviously, and if it's rigged conventionally on motor-down hoists it's also worth taking a little extra care with chain bags to prevent a spill.

 

If the truss is initially floated horizontal and then tilted in the air, obviously the points are going to tow at some point. Not necessarily a problem, but something to consider. There are sometimes circumstances where this could be trouble, particularly for longer trusses, steeper angles and lower roofs.

[michaelyallop]

er... it will be the same as if the truss was horizontal. As long as the points are hanging vertically.

 

This is not strictly true as the centre of gravity will shift down the angle when it is titled. The amount of difference depends on the angle, but near vertical obviously most of the weight will be on the upper most rigging point. I have just rigged a very similar grid this week. As long as you know the overall weight of the Grid and over spec each hanging point then you should be ok. Each of my hanging points can hold the overall weight of entire grid as it is less than 300KG, but obviously the more the grid weighs the greater the rigging points would need to be.

[ontoprigger]

As pointed out above the load on the points will be determined by the exact angle the truss ends up, as a rule you should never rig to 100% of the point capacity I always try and keep to below 70% and if you will have people climbing on the truss at any point for focusing etc. then that needs to be included in the calculations.

 

Rigging a third or pivot point will only help if the loads are balanced and the only way to truly know this is with the use of load cells, in my opinion these should be used when ever rigging motors and many fixed points, as they are now readily available and shows you the true load of the rig not what someone has guessed at...