by MelroseMatt
fishmech wrote:I do wonder why the PRR hadn't converted its New York City area swing bridges to lift bridges (Including both Portal and the Raritan Bay one). It's my understanding that lift bridges are both more reliable in general as well as easierEarlier this year I started working for a company that does engineering work (Design, Inspection, Construction Services) related to movable railroad and highway bridges. So some of the maintenance personnel and operators on this bored definitely have more experience living with these bridges.
I can tell you that a lift bridge is generally more complicated and more expensive than a swing span. Wire ropes bring their own expense, and maintenance requirements. The machinery on a swing bridge generally consists of a motor, a brake, a reducer, and a vertical shaft pinion to drive against a rack mounted on the pier. No ropes or drums or counterweights. Either can open or close quickly - this basically just depend on how much horsepower the owner wants to pay for.
Swing spans do require more clearance over the water than other types however, and access for major maintenance usually requires a barge crane.
The bridges are designed for 100 year service lives, and can last much longer. (I inspected a 130 year old span in CT in tip top shape). Mostly, what I've seen, is that the structure needs constant painting, and the machinery needs constant grease if the owner can do that, the bridge will last a very long time.
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