If a horizontal 13 guage pipe of 2 3/8" diameter carries a given evenly distributed load over a given span, what diameter would 2 smaller dia pipes of the same guage have to be to carry the same load over the same span?
This illustration may help to clarify;
Hi. Paul;
I am no Engineer, but would 1 1/4" twice come close to the right answer?
Just curious. ha. ha.
Marcel 
Pipes are not generally load bearing members.
I get 1-3/16 HINT-THINK ABOUT CIRCUMFRENCE
Brian; I think we all know that, but can you solve the equation?
Marcel;)
Hi. Mike;
I guess we are on the same page on this one.
I tried 1 3/16", but found I was under by .028 of an inch and over by .009214 by using 1 1/4".
I gather we are both talking about Dross Sectional areas?
Marcel
It depends on if you want the same deflection or the same maximum stress level in each pipe.
In a nutshell, you need to look at the moment of inertia property of each tube. For the double tube configuration, you need to assume that each tube is carrying 1/2 the total load. There are several other assumptions that will be needed to make (same materials, depth/span ratio, etc.), but the most important one for this case is that the material is the same.
The stress AND the deflection are both inversely proportional to the moment of inertia. So, if you know the moment of inertia for the single tube setup and want the same stress level and deflection for the double tube setup, you want the moment of inertia for each of the smaller tubes to be 1/2 that of the big one.
Q.E.D. (“quod erat demonstrandum”)
Yes but that’s way too much work. 
Think about how an arch works in transfering the load at the top of the arch to the vertical “column”:mrgreen:
So, what is your conclusion analysis??
Wasn’t there something on the BB last year about how (i’m talking flow and volume now) two 1/2" pipe doesn’t equal the same as one 1" pipe? does the same apply here? Not to mention that the thickness of the material is the same in both sizes so the smaller pipe should hold more weight if you think of it on a 1.1 scale.
Perhaps will Paul return and tell us.
I does not look lioke an equation to me Marcel, it looks like using something made to do one job, and then asking it to do another job.
Not enough info. Is it seamless material? Is the piping metal, plastic? is the piping supported by hangers?
What weighs more 1 lbs of lead pipe or 1 lbs of Aluminum pipe?
Tell me who made the pipe and I will google the answer.
Your thinkg too hard Brian. Maybe it will be clear in the morning when the head clears up.
Perhaps, perhaps not.
It seems I can still manipulate the spell check feature.
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Yep, forgot to spellcheck that one. (Good catch) Better put my glasses on or buy a bigger monitor;-)
I would guess 1 1/4" or less, but it changes with the span doesn’t it?
http://www.hooverfence.com/pipe-fittings/kee-klamp/specs.htm
Almost every underground pipe is load bearing.
From a structural point of view (not mechanical) I would guess X about 2" or a little less.
So two 2" OD pipes would carry the same load as one 2 3/8" pipe???
Seems like quite a safety factor.
I would call the material structural tube steel myself.
Thanks Brian, I should have said [FONT=Verdana][FONT=Comic Sans MS]structural steel tube steel [/FONT][/FONT]instead of pipe. My mistake.
They are for space frame structures such as Coveralls
Me to
In this case I think maximum stress level
Each smaller tube carries 1/2 the load.
Same material
depthspan ratio: That’s the key The span stays the same but because the dia. of smaller tubes the depth reduces. But you are also have a redistrubution in the material.
The application is indeed an arch. Click here
Sorry, I diddn’t mean to imply this was an educational excercise. I don’t have the answer. I’m looking for the answer for a real application.
Not seamless (too expensive) steel tubing. No hangers as such but that wouldn’t factor in becaise the span in both cases are same.
So the two smaller pipes would almost have to be as big as the larger one? :shock:
Does the webing in between the tubing make a difference in the capacity to carry the load? I would think it does, does that change the equation?
