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| Re: Lhota tells Long Island Association no East Side Access until 2019 (1156191) | |||
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Re: Lhota tells Long Island Association no East Side Access until 2019 |
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Posted by Outside the Box on Sat May 12 14:38:46 2012, in response to Re: Lhota tells Long Island Association no East Side Access until 2019, posted by WillD on Thu May 10 01:25:04 2012. Max vehicle weight on a bridge structure is partly a function of axle count and axle spacing. If you spread out the weight of a vehicle over a greater number of axles (and axle pairs), it will reduce the stress on the bridge. If you look at light rail, they weigh as little as 36 tons for 97' units. That weight is spread over 3 trucks and 6 axles. That comes out to ~6 tons per axle and double that per bogie. That is less than the El (>7tons) that ran over the bridge.The GT8-100C/D are heavier (59 tons), but not by much when you account for the number of axles and bogies. Spreading the weight over 4 bogies, and 8 axles result in 7.3 tons per axle and double that per bogie. That is similar to the BMT Q type that ran over the Queensboro Bridge (7.2t per axle). Similar vehicles are lighter than that. The upper deck was rebuilt in the 80's. The outer roadways were refurbished for vehicle traffic. Just because the northern roadway is a walkway doesn't mean it can't handle cars and trucks (20 tons). Its primary limitation is that it is too narrow for trucks. They had to retain one of the 2 for pedestrians and they chose the northern outer roadway. As for structure loading, there are ways to mitigate loads. Instead of conventional track and ties, use slab track or ladder track. That will greatly reduces shear forces and gradually ramp up and down force onset by spreading out loads under the wheel rail contact point over much longer lengths. LR55 and other modern ladder tracks are available. They take much of the beating and are much cheaper and easier to replace than bridge girders and chords. |
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