I was on the Mianus River I-95 bridge (near Greenwich Connecticut) three times the afternoon before it collapsed in the early morning resulting in deaths. One of the results was to build a weigh station abutting singer/entertainer Diana Ross's place. I have often gone past it a number of times, it's on the western side closer to the traffic leaving the "New York" side and have often seen it empty. It appears to me that it probably should have been on the other side to get the traffic coming toward NYC than the traffic leaving, but I have not seen the traffic volume studies.
Inspection is a problem on those types and one unique solution I've seen on-line was employed by the California DOT. They have a rotary engine powered ducted-fan on a umbilical control tether with video to inspect under their overpasses. Like the Mazda RX-4 I once owned, the rotary engine, credited to Wankel, has also been used in personal planes, burning regular instead of aviation fuel at the same rate and power output. NASA, I read worked on the seals that contain the combustion and resulting gas passed as power and exhaust on the 3 apexes of the triangular "piston," an engine with less moving parts to service and repair though the seals could wear out.
When one of the smaller wire cables stretching from the large suspension cables to the roadway holding the Brooklyn Bridge out over the East River, between the two towers which my great-grandfather helped build as a mason (Panama Canal too), broke, there was an investigation into the cause. One of the problems that can happen with metal is what the Brookhaven National Laboratory on Long Island, NY looked for, called "hydrogen migration" which occurs from the exposure to hydrogen gas, which it's said causes a brittleness of iron as it "migrates" through the interstitial spaces between the ferrous molecules. It's thought to be a problem in the storage of hydrogen as an alternative fuel to petroleum based products. As I recall it was found not to be the cause and the pigeon's excrement exposure, and the wire "rope" continually under tension, was what caused it to snap, in a process as described in this article.
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