Circular truss

[AndyJones]

Hello Guys.

 

Before every one jumps on me I have done quite a bit of rigging. so would deem myself competent with general truss rigging. But I have never had to deal with circular truss. Is there anything different I need to know? The total weight needing to be hung comes in at 256kg.(not including rigging or motors yet) My plan at the moment was to use four points on the truss and pick the truss up at every 90 degree point with 500kg motors. Are there any other ways or ideas?

 

Many thanks

 

AndyJones

[jimbo7744]

Hi Andy,

 

The only time I've had to deal with circular truss was at the old Whitbread Brewery in London and we had a 8ish metre diameter circular truss. The oak beams in the venue meant that we could only pick it up off 4 points (90 deg to each other) and it was fine. As I remember it, it was Trilite as well so not IMO the strongest truss, but was fine.

 

We just used it like any other suitable truss.

 

 

Jimbo

 

edit for more detail

[Seano]

Is there anything different I need to know?

 

Nope, not really.

 

You don't say what diameter the circle is, but if the span between adjacent points is reasonable, four points should be fine. There should be some guidance available from the manufacturer regarding maximum span, loadings, etc.

If the truss bolts together, you should take care not to overtighten - the bolts work harder than they do on a straight truss, and are more prone to getting jammed.

 

Like a 4 point box truss, if any one motor is a bit out of step with the others, the entire load will be spread across two diagonally opposite points, subjecting the whole structure to a big old bending moment and making an appropriately sad face. So you need to take care that all four points are at the same height - the curve can make it difficult to judge by eye from below, so if you don't have a vantage point where you can see clearly that its level, its worth trimming it with tape measures or a disto.

 

All just the basic sensible stuff you already do, really.

G'luck.

[flypig]

Hi Andy.

 

All of what Jimbo and Seano have said.

 

Anything over an 8m diameter I try to pick up on 6 points if possible as it helps to even out the load a bit.

 

As Seano says, watch the trim as you go up and take it in easy stages.

 

One little trick for levelling I have used is to cut several lengths of VB cord to the final trim height you require (cut the same number as you have points), and lightly gaf these to the side of the lower (or outer lower) chord under the point position (do not tie the VB cord). You can then use a Disto for the final 'bump level'. Just (gently) yank the VB chord to release it once your happy with the trim.

 

IH

[simantec]

Flew a circular truss off 3 points at a car launch before.

 

(It was Mercedes so we wanted that three star thing happening)

 

Thomas provided the truss and calcs and it was a straightforward hang.

 

Three points would ensure that all the motors would always be loaded.

 

What you can hang where and how comes down to what ever the manufactures recommend.

 

They are normally happy to help so I would ask them.

 

I like the tapeing VB Cord (What is VB cord?) to the truss idea to trim it and have used multiple 50m tape measures in the same way to good effect, especially when the exact trim height is hard to figure out untill its up there and precision is important.

[Sam_Lowers]

Hi All,

 

You have been saying about rigging the truss and it all has to be level.

 

How is it done where the trussing is rigged at an angle - say 45 degrees or so?

 

Sam

[paulears]

We're talking about levelling a structure supported on multiple drops, and 'levelling' is really being used to explain the practice of adjusting each drop to make the thing hang properly - no sags that put undue strain on joints, or a level that is in fact an unwanted slope. If you want to deliberately hang a structure at an angle, the same procedure takes place. I suppose when we talk of levelling, we're really talking unstressing, and proper weight distribution, rather than parallel to the floor - although that is the common orientation.

[Chris Higgs]

Watch the cantilever!

Definitely enquire (the manufacturer, not the supplier) if in any doubt.

 

Edited because I couldn't remember how to reply to a post, doh!

[Seano]

We're talking about levelling a structure supported on multiple drops, and 'levelling' is really being used to explain the practice of adjusting each drop to make the thing hang properly - no sags that put undue strain on joints, or a level that is in fact an unwanted slope. If you want to deliberately hang a structure at an angle, the same procedure takes place.

 

Yep - what he said. When you're planning to hang something at an angle, its the usual practice to anticipate the final position when marking out the points.

For example - if planning to hang a circular truss at a jaunty angle you'd actually hang the motors around an ellipse in order to have the chains vertical when it hits trim. (Meaning that some of the motors would be towing outward as you pick the truss up off the floor.)