Omaha daily bee., 1897-05-02
STEEL TOWER OF THE NEW YORK EAST RIVER BRIDGE.

the foundation must rest is sixty feet be-
low, and the intervening mud and sand
for an area as large as that of the caisson
must all be removed. This is done by the
utilization of compressed air. AS the huge
box gradually sinks in the water under
the weight of the stone work piled upon
it, strong pumps force air into the working
chamber through tubes provided for the
purpose, forcing the water out. Thcu
workmen descend through an elevator pas
sage. which runs up through the caiGson,
At the bottom they find a large workroom.
lighted by electricity and having telephone
connection with the outside world. AS they
shovel up the earth from beneath their
feet they place 1t in the mouth of a blower,
which is simply a tube extending up to
the surface, and the pressure of the air
carries ii up through the tube. With these
conveuiences the bottom of a river bed is
not a bad place in which to work. The
greatest drawback is from the great air
pressure, which increases as the depth be-
comes greater.
IMPOSSIBLE TO BE LAZY.
The increased pressure is about one-half
pound for each foot of depth, or about two
atmospheres at the depth of sixty feet. The
first effect Of the great amount of oxygen
in this artificial atmosphere is to make the
men unusually active, so that even a lazy
man will feel invigorated and will make
his shovel fly rapidly, For this reason,
however, they can work for short hours
only, and they are subject to a peculiar
affection known as the "caisson disease,
but which the workmen themselves describe
as the bends"
When the rock foundation is reached the
rock is blasted and smoothed away until
a level surface is obtained. Then the work
men fill the room in which they have been
employed with concyete, and the column OF
masonry, which has been kept level with
4. -. 6 ntKEae N Cn1t1 and pnn-
tinuous foundation, on which the bridge
proper will rest.
In the present Brooklyn bridge this ma
sonry is continued for the whole height of
the towers, but in the new bridge the towers
will be of steel. The latter construction has
many advantages. For instance, in the pres
ent bridge the overs each weigh five times
as much as all the rect of the bridge, while
IN the new bridge the towers will weigh only
about the same as the main span. althougn
they will be sixty feet higher than those OF
the older structure. These towers will be
built of steel plates and angles and will
rest on the masonry piers just described
which will stand twenty~three feet above
high water, Steel is cheaper than masonry,
too, and less time is required for its erection.
1t may be remarked here that the substi-
tuition of steel for stone is an American
development and that for this reason Ameri-
can bridges are the lightest and cheapest in
the world,
AT the tops or the steel towers VIII be
sliding saddles, over which the four great
cables which are to sustain the bridge will
pass. These great wire ropes will be eigh-
teen inches in diameter, three inches larger
than those In the present bridge. Each
one of them will contain 6S, 900 separate
wires, each 3-16 OF an inch in diameter. To-
gether they will have a sustaining power OF
6S. 900 tons, or Pa tons for each wire. 1t
would be impossible TO transport one of
these huge cables after it is put together, so
the strands that go to make up each one
are made and tested separately at the fac
tory. and then strand by strand they are
strung across from pier to pier and fastened
together.
AS these cables are to support not only
the Il. 500 tons weight OF the bridge itself,
but the assumed live weight OF IL, 900 pounds
per lineal foot, 1t Is evident that they must
be not only strong in themselves, but they
must also be strongly anchored.
ANCHoRING THE BRIDGE.
The anchorages will be located between
300 aud 600 feet back OF the bridge piers at
each end. They will be of masonry, 1OOx150
feet. and together will weigh 100, 900 tons. or
thirteen times as much as the main span of
the bridge itself. The cables will be Sc
cured to them by plates and pins in the
strongest possible manner.
Next TO these essential features the most
thing about the new bridge will be