Aluminium Tube Shear Strength 2

[dawahar]

Looking for some assistance please.
I want to use an aluminium tube to retain a load, and need to find out what load it can hold before collapsing.
Tube is 63.5mm O/D 51.5 I/D and 2112mm in length
Tube is B.S H30-TF Grade
Shear Strength 218
Modular Elasticity 69
Tensile Strength Min 280 MPa

Any help would be much appreciated.

 

[izax1]

Since you are using s tube, I assume the loding is Torsional. Try Roark&Young. In the seventh edition you have some relevant formulas in table 10.1

 

[drawoh]

dawahar,

Is the tube loaded in direct shear, or bending, or torsion? If shear, is it single or double shear?

An engineer can do any of these analyses, and they can analyze all the other stuff you are doing that looks marginal. This is a job for a qualified person at your site.

If this is a shear load, why do you want to use tube, rather than solid bar of the same cross-sectional area?

What will be the consequences of this thing fails?

JHG

 

[dawahar]

Thanks for the replies,
Tube was selected as a replacement for square section aluminium which was used originally in a fixed position.The new load bar moves so the tube is better suited than the original square section.
The tube is used to retain barrels so the load could cause bending then shearing.
We could use solid bar if the tube is not strong enough, or add a 2nd tube inside the outer.
If the load bar fails then the barrels could be damaged or worst case they could fall onto someone.

 

[drawoh]

dawahar,

If something capable of shearing 2.5" aluminium tube, lands on someone, it will be catastrophic.

What you are trying to do is not clear.

The tube failing in shear or bending is not the only failure mode you have ot worry about. It sounds like you need a qualified engineer on site.

JHG

 

[dawahar]

Drawoh,
Thanks again for your replies, I understand your concerns regarding my questions.
But what I have is a system that has been in operation for many years and has been passed as safe to operate with a swl of 1350kg.
This original system used rectangular aluminium box section.
All I wanted to know was if I replaced the rectangular with tubular section, would the tubular section be strong enough to withstand 1350kg of load.
If the tube is not strong enough, I would then hopefully either add another tube internally or replace with solid aluminium bar.

The load is mobile i.e. it is within an HGV trailer. The bars are not designed to hold back the full load, only to ensure that when the rear doors of the trailer are opened, there is not a barrel waiting to roll out onto the driver.
Hope this makes it a bit clearer.

Aluminium is the preferred choice due to system working in damp conditions.

 

[izax1]

dawahar

"if I replaced the rectangular with tubular section, would the tubular section be strong enough to withstand 1350kg of load."

Maybe or maybe not....

It all will depend on:
- space available
- loading condition (bending/shear/torsion/axial)
- material in box vs material in tube
- etc.

A job for a qualified mechanical engineer.

 

[kingnero]

@ drawoh and izax1:
"A job for a qualified mechanical engineer."

I do not think it is that easy,
as the tubular section will deform heavily prior to break.
Might even tear depending on the grade of Al. that is used.

This depends on the geometry of its constraining housing and the loads, but even knowing those, it isn't something you can calculate easily.

I for one wouldn't know where to start, and would like to see the approach that is best used in this case.
I am not familiar with sacrificial deformation (or how it might be called in english - cfr. crash zones).

 

[chicopee]

Based on the statement that the aluminum post was in use for several years, and if I were unqualified to make an analysis I would use round tubing of not less than the wall thickness of the rectangular tube and of a diameter not less than the diagonal dimension of the rectangular tubing, provided that the same grade of aluminum is used.

 

[dhengr]

Dawahar:

If you replace a safely functioning load securement bar, made of rectangular section, with one made of round tubing which has greater section properties and is made of a material of equal or greater mechanical properties, you should be able to retain the same loadings that the older system did. This assumes that the loading doesn’t increase or change and that the manufacturing process and details does not weaken the load securement bar (cargo bars) some other way. And, if you don’t understand what that statement means, you are not qualified to be doing this design change.

I am always amazed at how little design, dimensional and loading info. people seem to think is needed to address a design problem like this. And, I am equally amazed at the fact that products like this might make it to market and onto the head of a truck driver, with so little real engineering experience and judgement being applied to their design and production. The final amazement is that companies allow their designers to come to E-Tips for engineering fundamentals that they should have learned in their first courses in Statics and Strength of Materials. This is a very basic problem, however a good complete design of this product is more complicated and involves some engineering experience and judgement, or help from one of your senior engineers. Get a local mentor, maybe your boss, so he knows what you don’t know and can guide you accordingly.

 

[desertfox]

Hi dawahar

As pointed out in other posts, the problem you have described is not complete for instance how far along the tube does the load act? what are the dimensions of the original rectangular tubing? and how was it orientated to the load?
One simple thing you can do to see if the cylinderical tube is strong enough is

1/ calculate the second moment of area of both tubes and compare them, they should be at least equal or the value for the cylinder should be greater than the rectangular, this second moment of area gives you a value of resistance to bending.

2/ Calculate the area in shear for both tubes and like the above the area for the cylinder tube should be at least equal to that of the rectangular, this will tell you whether or not it will fail in shear.

I have to assume though for the above to be valid that both the tubes have the same strengths and that the loads and there position don't change from the original system.

desertfox