Comments on: The swaying Manhattan Bridge

By: kathleen croaker

kathleen croaker — Mon, 10 Aug 2009 18:42:09 +0000

We rode across the bridge on 8/8/09 on one of the open-top tour buses, and looking down, I was very alarmed by being able to see down 2 to 3 stories of streets, buildings, cars, people, water, and NO railings(except concrete bumpers that looked 2 feet high!), NO barricade along the sides of the bridge, and creepy space below with narrow lanes to drive on. I am scared of heights, but I don’t think it’s unreasonable to expect better protective barriers. Am I missing something? From Minnesota, land of the 35W Bridge collapse of 2008…

By: paulb

paulb — Wed, 29 Jul 2009 14:30:42 +0000

Two possible reasons for putting the tracks toward the outside??, the first one pretty bizarre: Moisieff’s deflection theory seems to suggest that higher moments at different parts of the bridge could balance each other and somehow make the structure deflect less.

Or, that the tracks are placed at strong points with respect to the columns of the towers, and Moisieff thought this would compensate for the greater moment that positioning caused on the deck.

By: W. K. Lis

W. K. Lis — Wed, 29 Jul 2009 14:02:10 +0000

Another reason why an army must not march across any bridge, for fear of causing the bridge to collapse. They should break stride.

By: Andrew

Andrew — Wed, 29 Jul 2009 01:41:04 +0000

The bridge is owned, inspected, and maintained by NYCDOT, not NYCT. Only the tracks (and the signals and the trains) are NYCT’s.

And what do you have against the D and N?

By: Eric

Eric — Tue, 28 Jul 2009 22:32:32 +0000

The footage is awesome. The bridge jumping isn’t.

The jumping of the Manhattan Bridge has always creeped me out. The worst is when the train is stuck from delays and then see what feels like an overweight speeding truck zipping through the middle lanes.

By: paulb

paulb — Tue, 28 Jul 2009 22:02:15 +0000

This is awesome footage! But I don’t think it’s a problem anymore. As posted above, suspension bridges are supposed to flex, and this must be much less than the huge, problematic displacements that were observed before the “torque tube” was added to the bridge during the reconstruction.

Blame, according to Sharon Reier in “The Bridges of New York,” Tammany Hall. Its mayor, McClellan, vetoed an innovative steel eye-bar design by reform-appointee bridge commissioner Gustav Lindenthal in favor of the Moisieff bridge (the one that was built) which sent business for conventional steel wire cables the way of the Roebling Company. Moisieff did not adequately adapt Lindenthal’s work for the different cabling, and the Flxible Flyer bridge that caused trouble for so many years was the result. As Lindenthal’s other bridges were successes, it seems likely to me his original design, albeit unconventional, would have been a success as well.

One thing I’ve wondered about the torque tube: Didn’t all the new steel add a lot of weight to the bridge? You’d think that would be a problem. (You can easily see the new steel of the torque tube when you are crossing the bridge.)

By: @epc

@epc — Tue, 28 Jul 2009 13:44:13 +0000

“For reasons that are now unexplainable, Moisseiff decided to run the subway train tracks along the outer edges of the roadway, instead of running them down the middle. As a result, the subway cars exerted incredible torque on the structure. The workhorse, it turns out, was a bucking bronco—its deck tilting as much as eight feet under the weight of a loaded train, forcing suspension cables to shift relative to and abrade against the steel trusses.”

From: http://www.siny.org/media/projects/mbr.pdf

By: Peter

Peter — Tue, 28 Jul 2009 12:29:22 +0000

Galloping Gertie (the Tacoma Narrows Bridge) it aint, but still a very interesting view. Too many people take complicated engineering & construction for granted.

By: Makes You NOT Want To Go Across The Manhatten Bridge « Being Grown and Sexy

Makes You NOT Want To Go Across The Manhatten Bridge « Being Grown and Sexy — Tue, 28 Jul 2009 11:38:44 +0000

[...] And I quote: When the Manhattan Bridge was first built, it contained a huge engineering flaw. Because the four subway tracks — two on the south side and two on the north — were built on the outside of the bridge as opposed to the center, the bridge would sway as the heavy trains drove back and forth between Brooklyn and Manhattan. As trains — and people — grew heavier, so did the stress on the bridge. [...]

By: Lawrence Velazquez

Lawrence Velazquez — Tue, 28 Jul 2009 09:38:07 +0000

The swaying is not a problem per se; after all, suspension bridges are built to sway. I recall reading somewhere that it was the unevenness of the swaying that’s been the real problem over time. That is, the north side of the bridge has always had heavier rail traffic than the south side, so the bridge experiences a sort of net torque in that direction.

Don’t quote me on that, though, or take anything I say as technical expertise. I’m a computer science major, not a civil engineer.