Above Ground

by Don Friedman on February 15, 2017

That’s the intersection of 51st Street and Park Avenue, taken from a bit south of the southeast corner, looking northwest. The green-glass building diagonally across is the Lever House.

The reason I took this photo is the expansion joint that runs across Park Avenue – it’s the straight line cutting across the driving lanes just behind the parked car. (There is some recent repair of a pothole at the edge of the expansion joint right where the car is, which is why the dark line suddenly widens.) The joint continues onto the sidewalk, where it’s covered by a wide steel plate.

Expansion joints are included in structures when different parts have a natural tendency to move differently. They are put in curtain walls to allow non-structural facades to move separately from building frames when exposed to changes in temperature or lateral load; they are put in structural frame for buildings with very large footprints to allow different parts of the buildings to move independently. We don’t think of the ground as needing expansion joints…and it doesn’t. But this part of Park Avenue isn’t the ground.

There’s been a dead-end train station at Park Avenue and 42nd Street since 1871. The current terminal is the third Grand Central at this location and the first without a grade-level train yard. The train yards of the first two stations chewed up a large piece of midtown and, thanks to the coal-burning engines that made the New York Central Railroad great, polluted everything nearby. The third station was built because (a) the second station was overwhelmed by the increase in traffic circa 1900 and (b) New York City outlawed steam engines, and so the Central had to go electric, at least for part of its lines. The use of electric trains allowed the train yard to be put underground – it could have been put underground earlier, but suffocating all of one’s passengers is frowned upon in the railroad business – and the Central did so in a big way.

There are two levels of yard in the approach to the station (the station is on the left, north is on the right) corresponding to the two levels of platforms and tracks in Grand Central. The east (bottom) and west (top) bounds of the yard are more or less Lexington and Madison Avenues, making the yard two blocks wide; the four-track approach widens to eight tracks above 56th Street and continues widening from there as it heads south toward 42nd Street.

The street in the top photo isn’t asphalt and concrete resting on soil, like most streets. It’s asphalt over the concrete roof of an enormous underground cavern full of train tracks. And the expansion joints are needed to handle thermal movement of that roof as the weather changes. It’s actually possible to trace the perimeter of the buried train yard by looking for the expansion joints in Park Avenue and the side streets.

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