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?
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.
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.
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
In this case I think maximum stress level
Each smaller tube carries 1/2 the load.
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.