Deflection calculation

beyond the blue

beyond the blue

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Neil
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I have been trying to work this out with online calculators etc. but can't come up with an answer. I am working on a project (non photographic) that uses Aluminium round tubes. Before ordering the tube i would like to determine how much the tube would deflect in the centre with a given weight applied to the centre.

Tube size = 7/8" (22.22mm) O/D
Wall thickness = 16swg (1.6mm)
Tube length = 71" (1.8mtr)
Weight applied to centre of tube = 2lb (.9kg)

The tube will not be fixed at each end as such, so will not help with any loading. If anyone can help with this calc or know of any calculator that will accept these measurements I would appreciate your help.
 
2.2 inches
 
kendo1 said:
There is an online calculator:
http://www.engineering.com/calculators/beams.htm#tube
scroll down to tube, enter values as decimal points if under 1, different materials available.
Click to expand...

Ken, Did you get that answer from that calculator? I tried that one but it never gives me an answer. If it's 2.2 inches then it's back to the drawing board I'm afraid. Thanks

Yep! working on main computer but not on tablet for some reason. Thanks again.
 
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Worked for me first time on a laptop.
The deflection seems about right for the material, size and weight.
Is there any way to spread the weight? Spreading the weight over the middle foot or so would bring the deflection down to around 1 inch.
 
kendo1 said:
Worked for me first time on a laptop.
The deflection seems about right for the material, size and weight.
Is there any way to spread the weight? Spreading the weight over the middle foot or so would bring the deflection down to around 1 inch.
Click to expand...

In actual fact it would be spread over over the entire length in a fashion. I was working on worse case scenario. I could tell you what i'm doing but it would take drawings to explain and I don't want to bore you;)
 
Using steel would bring it down to 1/2 an inch...
 
chadders said:
It's a simply supported beam; not a fixed beam.
Click to expand...


Correct! It's actually a retractable canvas cover for a garden pergola. I am trying to determain the size of Aluminium tubes needed to support the canvas. The ends of the tubes hang from steel rollers in a guide track, so don't add to the support strength, if you get my drift. Told you it was boring:sleep:
 
beyond the blue said:
Correct! It's actually a retractable canvas cover for a garden pergola. I am trying to determain the size of Aluminium tubes needed to support the canvas. The ends of the tubes hang from steel rollers in a guide track, so don't add to the support strength, if you get my drift. Told you it was boring:sleep:
Click to expand...

What is the 2 lb concentrated load at mid span?
 
beyond the blue said:
It's a retractable canvas cover for a garden pergola. Tere


Rain water in each section before each section will close together and water SHOULD run out.
Click to expand...

I can't quite picture your design, but if it's rainwater it's sounds more like a distributed load rather than a concentrated one.
 
That's not a point load.
... and it wouldn't matter if you put a slight slope on the ends/supports so that water ran off one side- one end higher than the other.
It only needs to be 25mm of a difference.
The only worry would be snow :)
 
What you have is a UDL (as opposed to your point load) based on a given volume (depending upon the depth) of rain water in each of those canvas sections. You may want to consider a factor of safety on the load you calculate.


You'll find Young's Modulus for aluminium by googling. You'll also need the value of I (moment of inertia) for your proposed tube. You'll also find a calculator for that on line.

You'll find an online calculator here:
http://civilengineer.webinfolist.com/str/sdcalcuf.php

Note you'll have to use SI units for your calc.

If the answer is not acceptable consider what options you have for using tube with a greater wall thickness.
 
chadders said:
What you have is a UDL (as opposed to your point load) based on a given volume (depending upon the depth) of rain water in each of those canvas sections. You may want to consider a factor of safety on the load you calculate.


You'll find Young's Modulus for aluminium by googling. You'll also need the value of I (moment of inertia) for your proposed tube. You'll also find a calculator for that on line.

You'll find an online calculator here:
http://civilengineer.webinfolist.com/str/sdcalcuf.php

Note you'll have to use SI units for your calc.

If the answer is not acceptable consider what options you have for using tube with a greater wall thickness.
Click to expand...

Wooosh
 
Or put a slope on it ( :D Clarkson has a lot to answer for ) and it doesn't matter about loads. If rain water does not stay in it there is no load apart from the weight of the canvas/ wet canvas.
Why make life difficult?
 
kendo1 said:
Or put a slope on it ( :D Clarkson has a lot to answer for ) and it doesn't matter about loads. If rain water does not stay in it there is no load apart from the weight of the canvas/ wet canvas.
Why make life difficult?
Click to expand...

Indeed; stick some drain holes in the canopy. Just don't use it as a rain shelter! Alternatively, close it if rain is forecast.
 
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