The arch was erected
without false work.
[Illustration: SHOWING CONCRETE OVER IRON WORK--HARLEM RIVER TUNNEL]
The viaduct spans of either approach to the arch are 46 to 72 feet
long. All transverse girders are 31 feet 4 inches long, and have a 70
x 3/8-inch web plate and four 6 x 4-inch angles. The two outside
longitudinal girders of deck spans are 72 inches deep and the other 36
inches. All are 3/8-inch thick and their four flange angles vary in
size from 5 x 3-1/2 to 6 x 6 inches, and on the longest spans there
are flange plates. At each end of the viaduct there is a through span
with 90-inch web longitudinal girders.
Each track was proportioned for a dead load of 330 pounds per lineal
foot and a live load of 25,000 pounds per axle. The axle spacing in
the truck was 5 feet and the pairs of axles were alternately 27 and 9
feet apart. The traction load was taken at 20 per cent. of the live
load, and a wind pressure of 500 pounds per lineal foot was assumed
over the whole structure.
[Sidenote: _Tubes under
Harlem River_]
One of the most interesting sections of the work is that which
approaches and passes under the Harlem River, carrying the two tracks
of the East Side line. The War Department required a minimum depth of
20 feet in the river at low tide, which fixed the elevation of the
roof of the submerged part of the tunnel. This part of the line, 641
feet long, consists of twin single-track cast-iron cylinders 16 feet
in diameter enveloped in a large mass of concrete and lined with the
same material.
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