Almost on cue, an example of exactly what I was concerned about: Sherman-Minton bridge in Louisville shut down. I’d love to hear a credible estimate of the weekly economic cost of having that route shut down.

For the past few months I’ve been staying in Seoul and marveling every day at the investments here: in transportation, healthcare, business, education, parks, housing, etc. etc. etc. Seeing all these things done right here makes me really worry about the future of our country, above and beyond the obvious political and macroeconomic concerns. I’ve recently started trying to get my thoughts down at http://log.shilman.net.

I’m really inspired by this principles-based look at things and will use it as yet another lens through which to understand what’s going on here in Seoul. Please keep these posts coming!

I’m not so much worried all the bridges are going to collapse; I’m worried a bunch of them will get so bad that they’ll have to be shut down, and an anemic economy (which would have been improved by, say, bridge-maintenence and building) won’t be able to provide the funding to replace them, further impeding transportation and hurting the economy even more. Same goes for water mains, sewer systems, the grid, etc. The purse-string people only have as big a purse as we give them.

You pretty much got it right. The hanger assembly is under the expansion joint, and they haven’t invented the good one of those yet–though they keep trying.

As for “stitch in time”–it isn’t quigte as bad as you make out. Every bridge in the US is inspected at least every two years, “Arm’s Reach”, ie from right close up. Some are inspected more often, if they’re in poorer shape. It is standard practice to replace those hangers with splice plates, and to eliminate the joint openings in the decks so salty water doesn’t attack the steel. This is done as funds are available, and as bridge conditions require, and it is a judgement call by people holding purse strings–but the work does get done.

And the bit about how there are several “I beams” (actually Wide Flange Sections, or W shapes): That’s called Redundancy, and is an important factor in bridge design. This was first realized in the Silver Bridge collapse of 1966. This bridge had been designed in such a way that a single crack in an eyebar caused the catastreophic collapse of a 1000 foor suspension bridge. Now we design so that, if one member fails, the bridge might be unusable, but it won’t fall.

If you have any more bridge-type questions, send me an E-mail.

Chas, PE SE, NHI qualified bridge inspector, and currently unemployed.