The method employed for the work
(Photograph on page 56) was similar to that used under Central
Park. The shafts at 168th Street and at 181st Street were located at
those points so that they might be used for the permanent elevator
equipment for the stations at these streets. These stations each have
an arch span of about 50 feet, lined with brick.
[Sidenote: _Steel Viaduct_]
The elevated viaduct construction extends from 125th Street to 133d
Street and from Dyckman Street to Bailey Avenue on the western branch,
and from Brook and Westchester Avenues to Bronx Park on the eastern, a
total distance of about 5 miles. The three-track viaducts are carried
on two column bents where the rail is not more than 29 feet above the
ground level, and on four-column towers for higher structures. In the
latter case, the posts of a tower are 29 feet apart transversely and
20 or 25 feet longitudinally, as a rule, and the towers are from 70 to
90 feet apart on centers. The tops of the towers have X-bracing and
the connecting spans have two panels of intermediate vertical sway
bracing between the three pairs of longitudinal girders. In the low
viaducts, where there are no towers, every fourth panel has zigzag
lateral bracing in the two panels between the pairs of longitudinal
girders.
[Illustration: PROFILE OF HARLEM RIVER TUNNEL AND APPROACHES]
[Illustration: SECTION OF HARLEM RIVER TUNNEL DURING CONSTRUCTION]
[Illustration: ASSEMBLING IRON WORK ON PONTOON--HARLEM RIVER TUNNEL]
The towers have columns consisting as a rule of a 16 x 7/16-inch web
plate and four 6 x 4 x 5/8-inch bulb angles.
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