Ledger calculation (1 Viewer)

pride2iceman

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Good evening gents!

Just had an argument with a site engineer regarding Imposed load on a loading bay 4mL * 2mW with 1m bay length and 1m bay width, he was saying that it can be loaded up to 10kN/m2.

By my calculations maximum loading would be about 4.8kN/m2, anything above that wouldn't pass ledger calculation (added 25% due to mechanical loading).
For ledger calculation applied this formula from TG20:13, page 142 M=0.167*P*L

And for transom calculation page 139 where M=0.086*W*L
Am i doing it wrong?

Any advice would be much appreciated!
 
First things first,

1) what does your drawing show?
2) What loadings are specified on the design?
3) the loading tower is capable of taking whatever the designer says not what the site engineer thinks.

As you will see I assumed you have not built this in accordance with TG20:13 but have in fact built a T&F birdcage type scaffold, nothing wrong with that assuming you have a design????

Note the TG20:13 loading tower page 166 is a 10kN/mSq loading tower.
(what did your customer ask for?)

Dependent upon your configuration at the top at 1.0m c/c of transoms your 4.8kN call it 5.25kn/mSq UDL with deck would give you a BM of around 0.65kNm and a reaction at centre support of around 6.6kN. (consider fittings) erect fitting on fitting.
At 10kN plus deck you will be at around double these results thus would require more transoms and supplementary couplers.

If built on a 1m x 1m grid with twin transoms local to ledger standard connection (say within 0.1m either side your leg reaction could be say 11.5kN (fittings) Moment on ledger could be around 0.61kNm

So in theory not too scary?
NOTE!!
This is not a design just an opinion with I would guess only a fragment of the information required to prepare a design, If you do not have one get a drawing and calculations.
 
You could get that to work if you put the transoms in at 500mm centres, one to the middle of the bay and 1 at the standard position. Assuming you have the boards running the long direction; Load on transom per span = 10.0 kN/m² + 0.25 kN/m² boards x 1.0m x 0.50m = 5.13 kN. From steel designers manual (which is more accurate that TG20:13 for continuous tubes on a structure of this size), BM on transoms = 5.13 kN x 1.0m x 0.125 coefficient (2 bays wide) = 0.64 kN.m. Reaction at central ledger = 5.13 kN x 1.25 coefficient = 6.41 kN. Bending moment in ledger = 6.41 kN x 1.0m x 0.170 coefficent = 1.09 kN.m which is less than the 1.12 kN.m SWL for a new tube. The reaction at the standard (load on couplers) would be approximately 6.41 kN x 2 = 12.81 kN meaning you would need class B doubles to connect the ledger to the standard with a class B double check below, structural transom normally does this job.

---------- Post added at 09:49 AM ---------- Previous post was at 09:45 AM ----------

Or as Alan says above you could actually locate the transoms tight to the standards at 1.0m centres which would reduce the bending moment in the ledger. You would then be relying on the board to take the load over a 1.0m span which is fine for a UDL but not if they are going to be using pallet trucks or similar with heavy loads. For this type of job it is essential to find out exactly what is being loaded onto the scaffold and how the load will be applied (pallet, wheels, beams, 4 legs etc.) and calculate based on the actual loadings.
 
You could get that to work if you put the transoms in at 500mm centres, one to the middle of the bay and 1 at the standard position. Assuming you have the boards running the long direction; Load on transom per span = 10.0 kN/m² + 0.25 kN/m² boards x 1.0m x 0.50m = 5.13 kN. From steel designers manual (which is more accurate that TG20:13 for continuous tubes on a structure of this size), BM on transoms = 5.13 kN x 1.0m x 0.125 coefficient (2 bays wide) = 0.64 kN.m. Reaction at central ledger = 5.13 kN x 1.25 coefficient = 6.41 kN. Bending moment in ledger = 6.41 kN x 1.0m x 0.170 coefficent = 1.09 kN.m which is less than the 1.12 kN.m SWL for a new tube. The reaction at the standard (load on couplers) would be approximately 6.41 kN x 2 = 12.81 kN meaning you would need class B doubles to connect the ledger to the standard with a class B double check below, structural transom normally does this job.

---------- Post added at 09:49 AM ---------- Previous post was at 09:45 AM ----------

Or as Alan says above you could actually locate the transoms tight to the standards at 1.0m centres which would reduce the bending moment in the ledger. You would then be relying on the board to take the load over a 1.0m span which is fine for a UDL but not if they are going to be using pallet trucks or similar with heavy loads. For this type of job it is essential to find out exactly what is being loaded onto the scaffold and how the load will be applied (pallet, wheels, beams, 4 legs etc.) and calculate based on the actual loadings.

As you say, It's all about what the load looks like a UDL seldom turns out to be a UDL!!
 
Should I get involved or not?

A 1m x 1m grid supporting ledgers & transoms (no beams) can be proven to support a udl of 10 kN/m2. It does need a little work in arranging transoms and it does need check couplers (properly called supplementary couplers) on internal ledger to standard connections.

Your loading bay has a capacity of 8 tonnes uniformly spread over the whole platform. Unfortunately, loading bays are not loaded this way so the figure of 10 kN/m2 is indicative only of a heavy duty loading bay good for the purposes described in the operations guide. If you want to design to European Standards, you have to consider all of the variations in the way that the loads can be applied. To do this you first have to know the number, weight and size of the loads and how they load the deck - eg point loads from steel stillages or knife edge loads from steel wheels or skids from pallets. You have to know how the loads get onto the loading bay - eg crane, forklift, hand stacking etc to determine dynamic loading. You then have to apply these loads to the platform in a variety of ways to produce the worst effects in all members. Don't forget that if there are joints in any members you have to allow for that. You should be able to cover all of the possible load cases and check a loading bay in a morning without breaking into a sweat if you get accurate information.
I would keep it simple and treat the load of 10 kN/m2 as a udl & take a little care in arranging the transoms as Alan says.
If you have the time, stop using factors to estimate moments and shear forces and support loads, think about a reasonable loading pattern on the deck and analyse it by hand using moment distribution or by computer and you will see where the critical points are. When you do this, you will see the difference between point loads and udl's. This is defined in the notes with the formulae (but perhaps not clearly enough based on the numbers originally quoted).
 
Thank you gents for clearing this out for me, it is much appreciated!

---------- Post added at 04:44 PM ---------- Previous post was at 03:31 PM ----------

You could get that to work if you put the transoms in at 500mm centres, one to the middle of the bay and 1 at the standard position. Assuming you have the boards running the long direction; Load on transom per span = 10.0 kN/m² + 0.25 kN/m² boards x 1.0m x 0.50m = 5.13 kN. From steel designers manual (which is more accurate that TG20:13 for continuous tubes on a structure of this size), BM on transoms = 5.13 kN x 1.0m x 0.125 coefficient (2 bays wide) = 0.64 kN.m. Reaction at central ledger = 5.13 kN x 1.25 coefficient = 6.41 kN. Bending moment in ledger = 6.41 kN x 1.0m x 0.170 coefficent = 1.09 kN.m which is less than the 1.12 kN.m SWL for a new tube. The reaction at the standard (load on couplers) would be approximately 6.41 kN x 2 = 12.81 kN meaning you would need class B doubles to connect the ledger to the standard with a class B double check below, structural transom normally does this job.

---------- Post added at 09:49 AM ---------- Previous post was at 09:45 AM ----------

Or as Alan says above you could actually locate the transoms tight to the standards at 1.0m centres which would reduce the bending moment in the ledger. You would then be relying on the board to take the load over a 1.0m span which is fine for a UDL but not if they are going to be using pallet trucks or similar with heavy loads. For this type of job it is essential to find out exactly what is being loaded onto the scaffold and how the load will be applied (pallet, wheels, beams, 4 legs etc.) and calculate based on the actual loadings.

What edition of Steel designers manual would be suitable for this calculation?
Could you refer to a specific chapter, please?
 
I use the 6th edition. Continuous beams start on page 1102 in this edition and unless they've added more load variations, or obtained the coefficients from more accurate software, this shouldn't have changed in the more recent editions.
 
I use the 6th edition. Continuous beams start on page 1102 in this edition and unless they've added more load variations, or obtained the coefficients from more accurate software, this shouldn't have changed in the more recent editions.

Thanks a lot, you are a DIAMOND!
 
Stop fcukin around & just ask your on site scaffolder - he or his mate will know the pukka way as theyve been buiding it the same way for the last 20 years & has never gone anywhere �� lol
 
Stop fcukin around & just ask your on site scaffolder - he or his mate will know the pukka way as theyve been buiding it the same way for the last 20 years & has never gone anywhere �� lol

That too.
 
Stop fcukin around & just ask your on site scaffolder - he or his mate will know the pukka way as theyve been buiding it the same way for the last 20 years & has never gone anywhere �� lol

Bless ya Southern, and 50 years before the scaff thought he was the only one who knew how it worked the design team did it :)
 
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