stress loading's for cantilever loading's (1 Viewer)

outward bound

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can i ask how do you work out the allowable loading's on a cantilever brace compared to the angle..im assuming that the loads was taken from the safe axial loads but surely this is based on a vertical tube within the allowable deviations. in the old guidance it was always 30 to 35 degrees for cantilever braces but in the the new tg20 guidance there is nothing now...?

cheers
OW
 
Don't know about anyone else but that doesn't make a word of sense to me, I have seen an engineer on here that seems clued up to the eyeballs with the sort of questions your asking.
 
can i ask how do you work out the allowable loading's on a cantilever brace compared to the angle..im assuming that the loads was taken from the safe axial loads but surely this is based on a vertical tube within the allowable deviations. in the old guidance it was always 30 to 35 degrees for cantilever braces but in the the new tg20 guidance there is nothing now...?

cheers
OW

"Triangulation"

Unless I misunderstand your question I feel you may have the horse before the cart.

I think you are asking about a brace being used as a spur to prop a cantilever. If not then I have misunderstood.

You would normally calculate the vertical load to be propped by the brace.
Once you have this you would resolve the vertical load through the brace angle using triangulation or trigonometry. As Scaffolders we would normally be working with a right angle somewhere in our triangle so:

The easiest way I find to explain this is as follows:
Pythagorean theorem
The length of the hypotenuse (Brace) is equal to, The square of the sum of the other two sides.

So consider the following
You are spuring the outer leg of an independent scaffold which is 1.2m wide in 2.0m lifts. The load in your outer leg is say 10kN

To find the load in your brace:
start by finding the brace length
You need the square route of (1.2x1.2)+(2x2)= 2.33m

Consider you 10kN as you vertical dimension and times it by your brace length=
10kN/2m =5 x 2.33m = 11.65kN in your brace thus you would need adequate couplers to support 11.65kN

You could reverse the process if you wanted to know the maximum vertical load which could be placed on a single coupler on your brace.

It sounded simpler in my head.

Good luck
Alan
 
Last edited:
Good response Alan!
OW, you're correct in that the angle from vertical should be less than 45° but we can calculate for any angle (within reason). Good practice for bracing angle is between 35-55° to allow the brace to carry vertical (tension) and horizontal loadings but for a raker or spur you want the angle from vertical to be as shallow as possible to reduce the axial load on the tube and the supporting couplers. The shallower angle also reduces the horizontal load imparted onto the ledger couplers, this is often overlooked.
 
lots of No.s here lads reducing the angle on the spur wont make any difference at all ,if your not at all sure simply double the cantilever spurs add additional needles along with a secondary cord to the centre of the spurs your cantilever is as only as strong as the scaffolding that its tied too.
And to be honest if the weight in question is for the cant and you are not sure of the stress capabilities for the load in question look at alternative for a truss out design with beams.always cover your arse cus theres always someone out there that will chase it scc
 
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