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Topic Title: Cable ladder
Topic Summary: Loading/recommendations of heavy duty cable ladder
Created On: 08 November 2017 12:40 AM
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 11 November 2017 11:20 AM
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basil.wallace

Posts: 251
Joined: 01 April 2006

Corrected as kg/km, Andy
 11 November 2017 07:38 PM
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leckie

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Hmm, well can anyone give me a bit of help with my question my post, like, how do you actually make the calculation? I am assuming that it could be done with the weight of the sum of a metre of cables, add additional required capacity ( say 25%), then add a safety factor, I think OMS said a factor of 3x, and would that be about it?

How to add an additional safety factor arithmetically for a grown man swing, I have no idea - I might need to ask for a clarification on that!

Marvellous isn't it
 11 November 2017 10:00 PM
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mapj1

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so, there is a pair of fixings every 'x' say 2m, usually more to do with the spacing if the girders above. So, 2m of tray/ladder or basket and its fixings weighs perhaps 4 kg, 2m of cables weight 4 kilos per cable, perhaps 5 cables in the bundle so 20kilos of cables per pair of supports, and one Jaymack weights 70kg. So, each pair of hangers where it is impossible for a person to hang on it needs rating for 24kg times safety factor, and each section where you think it possible there may be a body, needs rating for 90kg times safety factor.
This sets the type of suspension you may use or it may make you decide if moving things closer, or further apart, is desirable.
Clamps onto I beams and hangers and so on are usually easy to work out a rating. The big unknown is if you have something like rawlbolts going vertically into a concrete ceiling of uncertain provenance.

-------------------------
regards Mike
 12 November 2017 01:11 PM
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Jaymack

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Originally posted by: mapj1
The big unknown is if you have something like rawlbolts going vertically into a concrete ceiling of uncertain provenance.

Or providence.

Regards
 12 November 2017 02:13 PM
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Fm

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Are you using drop in anchors?
 12 November 2017 11:57 PM
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Fm

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Anchors,10mm screwed rod drops and 41x41mm uni with ladder hold down brackets on zebs and bolts
 13 November 2017 06:35 PM
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OMS

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Joined: 23 March 2004

Originally posted by: leckie

Hmm, well can anyone give me a bit of help with my question my post, like, how do you actually make the calculation? I am assuming that it could be done with the weight of the sum of a metre of cables, add additional required capacity ( say 25%), then add a safety factor, I think OMS said a factor of 3x, and would that be about it?

How to add an additional safety factor arithmetically for a grown man swing, I have no idea - I might need to ask for a clarification on that!

Marvellous isn't it


If we assume that you are putting 4 x 4C x 185mm2 cables on medium duty tray

1 - Decide on the deflection and thus the support spacings

Tray/m = 8Kg, cable/m = 4 x 6Kg - total = 32Kg

Assume something for extra capacity, etc so work on say 40Kg/m

40Kg/m = 400Newtons

Typical medium duty tray with a deflection of span/100 at 400N = 1.5M spacing

Taking the hangers at each end plus mid span these will be exposed to 40Kg x 3 m run = 120Kg and the load imposed on 6 hangers = 120/6 = 20Kg

Add a safety factor of say x 3 = 60Kg per fixing

For information, a 10mm2 threaded road would do about 175Kg (so you have this misuse margin here) normally and about 500Kg to fail

Looking at rawl bolts into reasonable concrete, the pull out of a M10 is about 600Kg - so just above the predicted fail of the rod

It's as easy, or as complicated as that

Most cable suspension systems are significantly over engineered based on industry custom and practice - or significantly under engineered down to cost - can we change the M10 to gripple wire sort of thing

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 13 November 2017 08:38 PM
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leckie

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Ah well, that's interesting, on bigger tray, say 300mm plus, we space at 1500mm on 10mm rod into 10mm anchors, with addional support at all ends, angles, tees of crossovers. So probably OK in most cases. Thanks for that OMS, I will put that calculation methodology onto my contract spreadsheet.

Praise the nerd!
 15 November 2017 05:40 AM
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basil.wallace

Posts: 251
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Looks good to me, OMS

I'll definitely will adopt your process for cable ladder.

Basil Wallace PgDip MIET EngTech
IET » Wiring and the regulations » Cable ladder

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