circle or square

glen76 · 24-10-2009, 06:16 AM

picture a flat grp surface with a formed shape on reverse side for rigidity.... whats the stronger shape, a semi circle or box section?? Like a stringer on the inner side of a hull for eg!!

marshan162 · 24-10-2009, 12:17 PM

For efficient use of materials i would guess a tringle, but it's only a guess

glen76 · 25-10-2009, 12:50 PM

strengthwise i meant. Im sure a continuous arc is stronger than a square isnt it??

marshan162 · 25-10-2009, 03:02 PM

I was considering strength, The beams of building site cranes are usually triangular in section.

JamesM · 25-10-2009, 11:16 PM

A triangle is the strongest geometric shape.

An arc is strong if the force is constant across its whole surface. That why pressure isolating or containing vessels are round.

What are you trying to achieve?

oxo · 25-10-2009, 11:44 PM

Triangular, just look at the strengtheners on the bow of any speedboat. For linear/lateral strength.

Hydrostream · 26-10-2009, 01:12 AM

For strength, I'd say square. It's a beam you're forming and needs two flanges and a web.

Jon Fuller · 26-10-2009, 09:01 AM

That's a complex subject.
I'd go with Hydro, but add that the height of the box you form is vital (in the same way that the thickness of Balsa, or foam is vital in a sandwich construction), and the uprights, or webs as hydro says, could be thinner (in other words the 'sides') and the top flange (top of box) should get extra laminate as that, and the main laminate you're attaching to are the 'flanges'.
That top flange will, when exposed to load, be expected to stretch/compress more than any other part of the stiffener because it and the main laminate are farthest from the neutral point (somewhere amid the web), so bears most if not all the load, so that needs to be STRONG.

motorvator · 26-10-2009, 10:33 AM

John is spot on treat it as you would a lever. The further you are from the centre of reaction the less force will be required so get the top as far away from the base as you can and give strength at that point.

Importantly though if using woven the important point is get the strand as straight as possible. Any bunching or variation from straight will want to unravel before it gets the chance to apply its full tensile or compressive strength.