tensile strength tube

savva said:
About 20 ton
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The working tensile load that a steel scaffold tube will carry is around 79 kN (about 8 tonnes).

This is based on the area of a 48.3 o/d tube 4mm wall thickness, no allowance for tolerance and no allowance for corrosion, made from steel with a yield stress of 235 N/mm2

The working tensile load that an alloy scaffold tube will carry is around 84 kN (around 8.5 tonnes)

This is based on the area of a 48.3 o/d tube 4.47mm wall thickness, no allowance for tolerance made from HE30TF alloy with a yield stress of 255 N/mm2.

Please don't use 20 tonnes as a working load, the tube will fail before it gets there

Does this help?
 
savva said:
Galv tube ? and alloy
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I'm not sure that I understand your comment but assume that it is a question asking why I have referred to steel tube when the original question referred to galv tube.

Steel tube is described as galvanized when it is treated, after manufacture by applying a zinc coating to it. I won't go into the process (you can look that up in the library - galvanizing & hot zinc coating) but it does not significantly alter the properties of the original steel tube or its cross sectional area. A galvanized tube has the same mechanical properties as the plain tube from the tube rolling or drawing mill from which it originated.

When new, plain steel tube, black tube and galvanized tube all carry the same loads. After 10 years, they carry different loads due to varying rates of corrosion.
 
Yes, I thought I'd throw that bit about getting the load into the tube in as well and then thought that it would only complicate things to start talking about eccentricities & moments :bigsmile:
 
What was used to calculate this was it s235 or the tensile strength of 340 N/mm2
 
The yield strength. For this type of steel, the result using yield strength is quite close to that using ultimate tensile strength (because of the different factors applied to get to a working stress value)
 
Can you explain tensile strength to a very interested thiko please. Is it vertical/horizontle length!?!??
In laymans terms please
 
tensile strength (n.) the strength of material expressed as the greatest longitudinal stress it can bear without tearing apart

I'm not just a pretty face you know.:)
 
Hi,

is the safe working load of the tube the same when used in standards, or will this change depending on the lift heights ?
 
Id imagine that the downward force would be the same, unless there is breaks (sleeves) in the tubes.

Horizontally strength varies but vertical strength should remain pretty much the same.


Im not an Engineer or anything - just a Scaffolder, but there guys here who would be able to give you better answers then me. :)
 
would it not depend on how high the lifts are and the standard spacing's or are you just talking about a tube ?
 
philliosmaximus said:
would it not depend on how high the lifts are and the standard spacing's or are you just talking about a tube ?
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It's worth noting that these figures were based on standard S255 tube.

Higher quality S355 tubing (and 25% lighter than S255) with a diameter of 48.3mm and a wall thickness of 3.2mm has a yield strength of 355 N/mm2.

Temporary works engineers generally make the assumtion that S255 tubing will be used if a data sheet is not attached when using S355.
 
outward bound said:
Hi,

is the safe working load of the tube the same when used in standards, or will this change depending on the lift heights ?
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Yes.

We started talking about the tensile strength which involved stretching a piece of tube until it broke. Now we're talking about compressive strength which involves squashing down on a piece of tube.

When the tube is very short, it will fail by crushing at about the same load as it broke when stretched. When the tube is very long, you will understand that it fails by bending sideways when it is loaded in compression. The load at which this happens depends on a combination of the length of the tube which is free to bend sideways and the size and wall thickness of the tube. Back in 1757 a Swiss mathematician called Euler worked out formulas for this which are still used today.

The length of tube which is free to bend sideways is related to the lift height and so standards with 1.5m lift heights carry more load than those with 2m lift heights which again carry more than those with 2.5m lift heights. It is made complicated by joints in the standard, the way that diagonal bracing is used and the way that ties are distributed across the scaffold and you have to look at each case individually. As a guide, a typical standard in a scaffold with 2m lift heights will carry a safe load of around 1.8 tonnes and the same standard with 2.5m lifts will carry 1.2 tonnes. Compare those with the failure tensile load which we talked about earlier and you can see that there is a big reduction from the load which you would calculate from knowing the the ultimate tensile stress and the area of the tube.

TG
 
Hi Chaps,

Just a little formula for you to work out the tensile capacity (F) of any tube if you have the yield strength (P) and the cross section area (A). If you just change the values of P and A depending on the type of tube then it will give you a permissible capacity.

Pressure = Force /Area
F = P x A

Where;

P = 235N/mm2
A = 55.7cm2

F = 235 x 55.7 x 10^2 = 130.895kN (ultimate load i.e. failure load)

Therefore, the factored load = 130.895 / 1.65FOS = 79.3kN

I hope this helps. If you have any questions please message me.

R.
 
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