Question for our resident engineer

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Havespannerwilltravel

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As we all know gravlock couplers have a SWL of 15KN for a vertical load only. Gravlock is not approved for use on vertical staunchions with horizontal tube where the load is also vertical as it could cause the gravlock to slip.
I have seen many jobs where the gravlock is used on vertical staunchions sometimes with another gravlock used as a check.
When I have questioned this I was told the design was done by an engineer and is ok.
Can an engineer go above manufactures recommendations?
 
Depends on the manufacturer but yes they do have some value in slip along the flange. I recommend you get hold of the data sheet for the exact "gravlock" being used.

I have one for the Boulton girder coupler (SGB) and that gives values in all 3 planes including slip along the flange....if you would like a copy PM me will be happy to send it on over.

No engineer will go against manufacturers recommendations to answer that question.
 
gravelock

used in pairs thats opposite connected by tube slip test will be 20kn also advise same procedure underneath as check never put to much in scaffolds to make safe

---------- Post added at 08:26 AM ---------- Previous post was at 08:23 AM ----------

used in pairs thats opposite connected by tube slip test will be 20kn also advise same procedure underneath as check you can never put to much in scaffolds to make safe
 
Info -Myself Personally have Doubts on the Vertical Loadings if Hanging off.
Our instructions to our Scaffs - Beam Clamps on Vertical For Scaffold Horizontal Tie in point Use only.
If still Probs & need to hang we visit & advise -(Look for way to Additional Support Vertical from other means ie:Angle of the dangle)
 

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  • Gravlock Girders Couplers.doc
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Last edited:
divit said:
used in pairs thats opposite connected by tube slip test will be 20kn also advise same procedure underneath as check never put to much in scaffolds to make safe

---------- Post added at 08:26 AM ---------- Previous post was at 08:23 AM ----------

used in pairs thats opposite connected by tube slip test will be 20kn also advise same procedure underneath as check you can never put to much in scaffolds to make safe
Click to expand...

The slip test on a pair of Bolton Girder Couplers in the 'XX" Axis is 1000kg. (Along the steel)
Girder Couplers should only ever be used in pairs.
I have never seen anything from a manufacturer referring to checking to gain added capacity.
However if I was using this direction to support a scaffold I was standing on I have no doubt I would check it!!
 
I have attached a Pdf, hope you can view it
 

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  • Girder Coupler 30001.pdf
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So which vertical load on a horizontal flange would you use?

1250 kg from Alan's pdf or 3000 kg from Stella's doc

(Boulton make Gravlocks)
 
Stella is only showing it one way, Alan is showing you different loads in different applications.
 
Yes, I understand that but the condition shown at the top left picture of Alan's sheet clearly shows that a pair of Gravlocks will only carry 1250 kg as a vertical load. That is the maximum load perpendicular to the flange and appears on the lower left picture as well. It is possible that it is the maximum load when applied in combination with the lateral load but I don't believe it is.
The brochure extract shows a swl of 3000 kg.
Both of these loads cannot be correct, so which one is the correct figure?
 
Hi
the information I have provided was an extract from a Boulton Group communication to SGB dated June 1995.
This may be out of date or superseded?
It may also be a different manufacturer of coupler and or tested to a later set of requirements.
I can supply the entire document if you think it useful. PM me your mail address I will forward a PDF

In the meantime I will root through my old files and see if I have anything more relevant
regards
Alan

---------- Post added at 11:55 AM ---------- Previous post was at 11:35 AM ----------

The Plot thickens!!
I have just pulled from my file an SGB Youngmans document Dated May 1996 showing a different set of results.
Y Axis (hanging off the steel)30kN a pair
x Axis (slip along the steel) 10kN
Z Axis (left to right across the steel) 6.5kN

PDF available if you PM your address
regards
Alan
 
I also have various data sheets and also test certificates for Gravloks, some of which show different loadings. The load I use for a pair of Gravloks hanging off a horizontal beam is 20.0 kN but this can be increased to 30.0 kN when using Presco girder couplers (which my company usually use). The loads Presco state for slip along the beam and slip along the tube are 12.5 kN. I believe the document is available on their website.
 
I also have a copy of the same sheet as Alan on curled up faded fax paper but it has Presco on the top. There is another sheet showing two beams, each with a Gravlock on it (opposing each other) and a swl of 625 kg per beam to give a total of 1250 kg. That is why I think that the single beam with two Gravlocks can carry a maximum of 1250 kg vertical load with no lateral load. I have no test data but the original Gravlock was an Audax fitting and I am fairly certain that they did in house testing so if the data came through that route, there will be no records of it by now.
The 30 kN is from a current Harsco brochure so there may be data available from the testing for that. (If they are swivels rather than doubles, the swl drops to 15 kN per pair.) It would be really useful if there is data for loads in other directions for both types but I would not be holding my breath.
Boulton are still around so I guess that they still make Gravlocks, Doughty Engineering sell Gravlocks with a swl of 600 kg and Presco do sell girder couplers but I wouldn't know whether they are all identical items.

All in all, I think that the 30 kN may be a deceptive figure to be passing around and I would really want to be 100% that the right coupler and the right method of use is being used before I went that high.
 
Presco do have test results showing that their girder couplers can take 30.0 kN for both the swivels and fixed (double) couplers. They were tested to Australian standard AS 1576.2-1991 so I'm not sure what the exact test procedure is but I would imagine they have a suitable factor of safety on top of the SWL's that they quote.
I also wouldn't 'pass around' a 30.0 kN figure and would only use couplers from a known source and a known strength in my designs.
 
The Aus/NZ test is a proof load of 30 kN (see below). They can pass that with a factor of safety of 1.1. I would be inclined to take a swl of less than 30 kN on the basis of a proof load test like this.

L4 PROCEDURE
The procedure shall be as follows:
(a) Fix the flange clamps in the test apparatus as shown in Figure L1.
(b) Tighten the clamp to the requirements of Clause 3.2.3.
(c) Subject the flange clamps to a tensile force of 30 kN, applied progressively over a
period of 90 s and hold it for 1 min −0, +15 s.
(d) Remove the force and record whether the flange clamps showed any permanent set.

---------- Post added at 02:53 PM ---------- Previous post was at 02:42 PM ----------

And for completeness:

The slip tests in both directions are also proof load ones, where, after tightening the bolts 5 times to a torque of 54Nm to stretch them, they are fitted to the girder & tightened again and left for 10 minutes. The load is then taken up to 6 kN for a pair, removed, the bolts are tightened and then the load is taken up to 12.5 kN. A pass is slip less than 6mm.

If that is the way that they are fitted on site, I would be happy to take a design slip load of 6.25 kN for a pair of Presco Girder Couplers fitted to a vertical flange.

This is by no means clear cut is it?
 
Been using em with a 3 t load on the drawing for a few years now.

Isnt it side loading thats a bigger issue, one beamy loaded really?
 
Vertical loading in general has a greater factor of safety because live loads are usually overstated. A live of load of (for instance) 1.5 kN/m2 on a normal independent is rarely achieved. Take a 4 + 2 scaffold 15m long and the total design load is close on 3 tonnes. Apart from bricklaying, would you ever see 3 tonnes of men and materials on 15m of a scaffold? The same applies to hanging birdcages where the load may be smaller but the area is larger. Because of this, the Gravlocks are very unlikely to ever actually be loaded to the figure shown on the drawing. Design the scaffold, calculate a loading for the Gravlock and keep it below 3 tonnes and you end up with a safe scaffold because of this. Design a hanging scaffold with a known weight on it and you may not have a safe scaffold. Take a small platform with 4 fixing points and a known weight of plant like a 12 tonne transformer on it - what safety factor do you have in this case - I don't know.

The point is that the standard to which the fittings are said to have been tested does not guarantee you a known safety factor if you use 3 tonnes (or any of the other proof loads in it) as a working load. Add to that the variety of safe loads quoted by different suppliers and you have an accident waiting to happen. I would suggest that the fact that we haven't had many accidents involving Gravlock copies may be luck rather than judgement.
 
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