Equilateral triangles are used in bridges all the time - but generally a series of little ones. I propose that the bridge be two huge equilateral triangles. The big ones would be filled with little ones to convey the weight from the bottom part up to the two sides of the triangle.

This would be
as effective as a bunch of small ones in regard to getting people across. But visually it would be much more dramatic.

Triangleshttp://www.google.c...0,i:235&tx=86&ty=93 Here is one big one filled with little ones. Maybe those little ones could be filled with littler ones. [bungston, Jul 02 2013]

Triangle bridgehttp://www.google.c...,i:253&tx=121&ty=61 But it has right triangles, not equilateral. [scad mientist, Jul 03 2013]

Portland Bridgeshttp://www.bizave.com/portland/bridges/ They did not think the 1970 one was pretty enough, if I understand right. [bungston, Jul 06 2013]

I'm having a hard time picturing this. Are the bridge openings triangular or is the suspension triangular? Horizontal or vertical triangles? Are the little ones inverting or in-line with the big ones?

Well, the same could be said for squares, circles, or dodecahedrons. Once you understand how a truss works, patterns emerge - but it's not as simple as saying "triangles are good".

...And once you're up to the scale of a bridge, it's normally all curves anyway, except for very old ones.

//The big ones would be filled with little ones to convey the weight from the bottom part up to the two sides of the triangle.//

It's like you kind-of know how a bridge works, but only sort-of.

No curves. No stuff hanging down. Nothing in the middle but a pointy point. Two big triangles. Car starts on one side of the triangle and drives across to the other.

One big triangle is pretty but pointless. Putting a little triangle upside-down in the middle of it (making 4 triangles) is better... but the top little triangle still doesn't do anything. Take the ^ away making sure to leave the - ('cuz that's what's doing all the work) and... you have what a small bridge usually looks like.

I think it would be more interesting without a uniform fill of the triangle. Specifically, I think a Sierpinski triangle would be very nice.

As [FlyingToaster] said, this isn't a huge departure from standard outdated truss bridge design like the one that just recently collapsed here in Washington State, but I will say that with a Sierpinski triangle, leaving the point on top ought to allow using a smaller beams because each beam is suported by a smaller Sierpinski triangle which will help prevent buckling (at least in one plane).

This makes me wonder if there are any structural benefits to a Sierpinski triangle used as a truss.

The triangular truss is largely outdated because
they are generally not
necessary. For shorter bridges, simple beam
bridges or box girder bridges are sufficient, for
longer bridges, arch (and yes, some are arch truss,
but they aren't triangular) are
stronger for less material, and for the longest
bridges either suspension or cable stay give you
the best strength for cost.

The one exception I've seen recently is prefab
pedestrian bridges where the truss forms the hand
rail, since the superstructure serves the dual
purpose.

If you used one of those fractal triangles...you know,
the ones where a smaller tringle is added along the
length of the previous triangle....you would never
finish the bridge...it would be permanent
employment....until down to nano-scales, at least.

Edit: I was going to edot "tringle" but decided to let it
stand.

I started pondering this after being told that the Portlanders protested a large bridge across their river because it was too ugly. Sturdy, cheap, very functional, but ugly. So if in bridges, aesthetics is worth some expense why not a big triangle? Agreed the top bit is just decorative but it comes cheap and offers some fearful symmetry.

Honestly, a central pier cable stay bridge approaches
this in shape, but not in function (the cables aren't
quite straight lines, but they're close). Just design
one where the outermost cables are 30 degrees off
vertical, and you'll get close enough.

It's technically impossible to pull a cable with a
horizontal run under gravity loading into a perfectly
straight line. Existing cable-stayed bridges approach
close enough if all you care about is appearances.

Cables, schmables. You can't swing a cat without hitting a bridge with cables. This is for a bridge to make a city proud. The two overlapping triangles would be the logo for the city. Kind of like the St Louis arch, but good for something.

I saw a Sierpinski triangle today and thought - "yeah! that is what the bridge needs to have". I see scad thought of this immediately and posted the anno but I feel good about that too. It is not the first time.

The trick to finsihing the bridge would be that the increased geometry would condense: the overall bridge would have 4 levels, then the section to the right 5, smaller subsection 6 and on down. The section where the triangles get really detailed comprise the wall of the visitors center / view deck. A lens is set up so you can view the smallest levels of detail.

I can see the city merch with the triangle, just like St Louis does with the arch.