Tuesday, October 09, 2007

Brute force, or grace?

Check out pictures of the bridge to replace the one that collapsed in Minneapolis. Notice that it's more or less a flat slab of a bridge trying to span 500' across the Big Muddy. I'm not one who thinks that it's not a bridge if it doesn't have some arches, but my rudimentary understanding of structures reminds me that one of the most difficult things to do, architecturally speaking, is to span a large distance without using some form of girder or arch in the design. Evidently, it's cheaper to install massive amounts of concrete and steel than it is to maximize the strength of a smaller amount of concrete and steel.

4 comments:

pentamom said...

Is this a public confidence thing, by any chance? Some officials have in their heads, (maybe rightly so) that after the bridge disaster, people will feel better about a visibly well-supported slab of concrete than they would about a network of "delicate," "flimsy-looking" arches?

I dunno, probably not, but that thought did come to mind.

Bike Bubba said...

Probably something to that, though I'd have to point out that if you want to look at a bridge that's lasted a century, you're going to see some arches. Perception vs. reality?

I'd also have to guess that part of the issue is the simple fact that it takes labor to do all of those arches & supports from them. $200/ton or so for steel & concrete is a lot cheaper than $50/hour for qualified ironworkers to put a bazillion rivets or bolts into a structure, I'd guess.

pentamom said...

Oh, sure, reality says that properly designed arches are just as supportive as, or better than, big hunks of "stuff."

But I was talking about perception. It's not the engineers and informed people of the world who drive political decisions these days, after all.

Bike Bubba said...

You know, it certainly would be interesting if those arches could be made actually cheaper than those monster chunks of concrete, and the public was presented with the evidence of which you speak.

I dare say it would sell some newspapers--why is the DOT rejecting the Golden Gate Bridge in favor of THIS?, and that sort of thing.