Jump to content

Flying truss using gripples


Dan Appleby

Recommended Posts

I was working in one of the seemingly thousands of marquees at the ryder cup over the last week, the lighting boys in the marquee I was in rigged the truss with a very interesting rigging scheme...

 

The main truss over the stage was a 10m by 10m sqaure truss - not sure what kind of truss it was, not that it matters, but it was lightwight trilite kind of stuff - hanging from 4 half tonne chain hoists. Hanging from the truss was probaly 25 or so smallish fixtures (you'll have to excuse my lack of knowledge of lighting gear - I am a noise boy after all!), all I can say is that they were fairly light (they weren't PARs). Also hanging from the truss was 4 of our d&b Q7 speakers. All fairly normal I hear you cry... excepet the WHOLE truss was supported using gripples and gripple wire - the hoists were attatched to the roof joists using it, and the truss was was attatched to the hoist with it.

 

The gripple wire has a SWL of 1T but the gripples only have a SWL of 300kg - the lighting boys seemed to think that you could hang 1.5T from the truss... We were supposed to be hanging a 3 drop of Q1 either side of the stage from it, but 'poliely declined', fearing that the truss (or more the gripples) wouldn't be able to take the extra weight.

 

Has anybody rigged using gripples before? how safe is it?

Link to comment
Share on other sites

  • Replies 40
  • Created
  • Last Reply
Has anybody rigged using gripples before? how safe is it?

I've used them from time to time, to tension horizontal guylines on things (flown followspot bridges, for example) to prevent them swinging about. And occasionally for hanging very light scenic elements, signage, etc. Their advantage is that they're so easy to adjust, so with some signage or a projection screen, that last minute request to lift it up a couple of inches is fairly unproblematic.

 

I seem to recall that Gripple weren't recommending them for lifting purposes for a while. (I may be wrong about that.) I thought that might still be the case, but I see from their website (http://www.gripple.com btw) that they do indeed have a properly specced SWL for lifting/suspension. The new lockable Gripple (6mm rope, rated at 500kG) looks very nice.

 

Unless the lampies you're referring to were using some kind of whizzo high spec rope though, I'm a little confused as to how the Gripple could have been rated for 300kG and the rope for 1t. With standard ropes, the Gripple is actually slightly stronger than the rope that fits in it. Incidentally, its essential that steel cored rather than (more common) fibre cored ropes are used with Gripples. (A good question to ask the next time you see this.)

 

I'm totally baffled as to why they were using Gripples as you describe. The adjustability of the Gripples is entirely irrelevant in a system where they're being used with hoists, it'd be neater, easier (and yeah, safer) to use slings and/or steels with swaged eyes.

 

If you see this again, any chance you could get some photos? I have a small but growing collection of pictures of some um... creative rigging - ranging from "well I suppose its safe enough, but why!?!" to "run away!". This sounds like it'd fit right in. ;)

 

Sean

x

Link to comment
Share on other sites

Sounds a bit scary... From my memory I didn't think that Gripples were supposed to be used for lifting at all, but a quick look at their website finds that they can be used for suspending STATIC loads.

 

I don't think you could class a lighting truss in a marquee raised and lowered by chain hoists to be a static load by any stretch of the imagination.

 

 

Sam

 

Edit: Seano got there before me...

Link to comment
Share on other sites

gripples can be used for catineries etc but definately NOT for flying truss with. I cant remember the reason off the top of my head but it has been this way for a number of years. if in doubt call a rigging company like Summit Steel.

 

'Cause if you look on the side of many gripples is says quite clearly "DO NOT USE FOR OVERHEAD LIFTING"

 

Thats on one of the ones I have kicking about, that happens to have a WLL of 400kg. which would in theory allow a combined load of 1.6T

(over the 4 points) Just not a suspended one! I think its something to do with the lack of a propper locking system (obviously different with the new locking one!)

 

Not that I ever use gripples. ;)

Link to comment
Share on other sites

I've inspected installations that have failed due to the use of Gripples, so I agree with the rest of the comments here. Personally I would only use them in very light weight situations well under the given SWL (light weight banners and the like).
Link to comment
Share on other sites

'Cause if you look on the side of many gripples is says quite clearly "DO NOT USE FOR OVERHEAD LIFTING"

I'm not sure about this. I don't know how the product has developed over time, maybe there are older units out there that aren't made (or tested) to the same spec as the current ones. (cf "rated" vs "unrated" shackles).

However, if you read the literature, another device that the manufacturer says must not be used for "overhead lifting" is the CM Lodestar.

 

You should of been there the day I tipped a bin full,due to an argument with a "rigger" who wanted to use them to make up some steels!

I'm still uncertain whether this is kosher or not, having never seriously contemplated using Gripples this way. Using any type of rope grip rather than swaged ends to make up fixed-length steels doesn't seem like doesn't seem like best practice to me, but looking at the spec on Gripple's website I can't see why they'd be less suitable than any other proprietary rope grip for the purpose.

You were obviously sufficiently certain of yourself to get into a fist fight over it that day, so care to post a definitive answer?

 

I've inspected installations that have failed due to the use of Gripples

Other than the fact that Gripples were involved, why? Was it a knee-jerk reaction to seeing that particular device, or do you have some documentation to back up your decision?

 

Personally I would only use them in very light weight situations well under the given SWL (light weight banners and the like).

Why? Do you not consider the manufacturer competent to determine the SWL of their own product? How have you determined that their "true" SWL is a different, much lower figure? Some sort of testing regime, or guesswork?

 

Hypothetical situation: An installation uses Gripples fully in accordance with the manufacturer's instructions. You're in a position of some authority, inspect the installation and declare it unsatisfactory. The installer has to do the work again, which costs them and/or their client money. They then take you to court, claiming that your decision to condemn the installation was unjustifiable and seeking to recover those costs. How do you defend the case?

 

I've only used Gripples to hang very light things too, but that is only because thats what they're most useful for. Banners, signage etc., stuff that can be lifted by hand and the Gripple allows very easy adjustment to trim height. But I would have no qualms at all about using one up to its SWL, because that is by definition a safe load to put on the device.

 

Sean

x

Link to comment
Share on other sites

One page on the Gripple site states "Do not use for lifting". As such you can't use them on a steel attached to a hoist of any kind, however, once the truss is up can you use them to suspend it? (All other things being equal, rating, point, attachment to truss etc)

 

The site shows many examples of "stuff" being suspended overhead.

Link to comment
Share on other sites

AFAIR the original Gripple could possibly let the rope slip if the load was lifted, and the retaining wedge lost its grip. The newer one appears to have a locking mechanism, but this requires tightening (with a tool?) to provide "security under dynamic load conditions".

 

Gripples seem fine when used in multiples for hanging drapes etc. - quick and easy to adjust. As Dan originally pointed out, flying a truss with motors and with heavy a loudspeaker load does not appear to be a suitable application.

 

Simon

Link to comment
Share on other sites

I have in the past used wire rope / thin steels to suspend a fastfold screen from a truss and used cable grips with screws to get the screen level correct. At the truss, the wire rope was just loopped around the truss and a second rope grip used, wuith the excess rope taped to teh truss for neatness. Would use of a gripple in this case be ok, or would this count as lifting since it would lift the screen from the ground when the truss (which is on 4 truss motors)) was lifted?
Link to comment
Share on other sites

One page on the Gripple site states

I haven't seen that, which page is it on, and which Gripple is it referring to? Can you post a link?

 

That would be Here

 

Now I'm not a time served rigger but looking at the website it seams that these devices were designed to be used in

static permanent industrial Installations.

 

Should we be using them in temporary dynamic structures at all?

 

Would it not be better to use bullets as pictured Here.

Link to comment
Share on other sites

Would use of a gripple in this case be ok, or would this count as lifting since it would lift the screen from the ground when the truss (which is on 4 truss motors)) was lifted?

The term "lifting" may be a bit ambiguous in this discussion.

 

There's much misunderstanding about "static" vs "dynamic" load too. There isn't some magical property that makes a dynamic load dangerous where a static load is safe - its merely that when things are moving, forces can be significantly more than you might expect at first glance, and its necessary to think about it carefully.

 

For example, when you lift something with a Model L Lodestar (the ubiquitous 1tonne motorised chain hoist) - as the motor begins to move it has to both support the load, and apply a bit more force to overcome its inertia and accelerate it upwards. This is usually reckoned to add about 25% to the load, so when you start up the motor to lift a 800Kg load, the lifting gear in the system briefly experiences the equivalent of a 1000Kg static load.

 

I think its reasonable to assume that if you're using a rope grip to suspend a screen from a truss, that suspension will also experience a transitory additional 25% (ish) load as the truss begins to move. What is the SWL of the rope/grips etc. that you're using, and how much does the screen weigh? Unless you're using very skinny ropes, I think its likely that the SWL exceeds the weight of the screen by a couple of hundred percent. If thats the case, its not something you need to worry about.

 

If you're looping a wire rope directly over the chord of a truss, a couple of unrelated things to be aware of:

  • Trussing is only designed to take a significant point load at certain points along its length. The weight of a fast-fold screen is unlikely to be "significant" in that sense, but its something you should be aware of. If in doubt, consult the truss manufacturer.
  • The rope is made of steel, which is harder than the aluminium the truss is made of. If you use a Gripple to loop a rope directly over a truss member, when you adjust it the rope slides over the truss in a sawing type action. It will actually begin to saw through the truss if you don't take care to prevent that. You shouldn't drag the rope across the truss member under load, for example by just hauling on the free end of the rope. Its also good practice to protect the truss with something, a small piece of cloth like some folded burlap or a piece of rubber matting, would be good.

hth

Sean

 

ps: Standard disclaimer applies: you're paying me nothing for my advice and thats what its worth. You 'int seen me, roight?

 

 

That would be Here

<snippage>

Would it not be better to use bullets as pictured Here.

 

I don't know, it seems a bit unclear to me. I'm very happy using Gripples for what I use them for. If I had any doubts, I'd consult Gripple themselves for a bit of clarification. Really the only definitive thing I can say is that if in doubt the thing to do is ask Gripple directly. They're based in the UK, they answer the phone, and I'm expect they're probably very nice people. ;)

 

My gut feeling on the second point is that if Gripples aren't good enough for something, bullets (aka "Quick Term" connectors) wouldn't be a suitable alternative. Both devices work on the same principle with a similar mechanism, and for a given size of rope a Gripple is a slightly stronger device.

Again, don't know. I may very well be wrong about that.

 

Sx

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.


×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.