Wessington Springs herald. (Wessington Springs, Aurora County, Dakota [S.D.]) 1883-1891, 1883-08-04
The New Niagara Bridge.

= Inc Canada oOuthern hallway Bridge
over Niagara River is to be built at a
point about three hundred feet above
the present suspension bridge. The
contractors have engaged, under a very
heavy penalty, to complete the whole
work by 1st December next, about eight
months from the time of beginning OPP
erations. The time occupied in build
ing the suspension bridge was three
years. A comparison will give an idea
of the vast progress made in recent
years in the art of bridge-building. The
new structure will embody a new prin-
ciple never before illustrated by any
large work actually finished. Two
similar bridges, however, are now be-
ing constructed-one the new Tay
bridge over the Firth of Forth, Scot
land, and the second for the Canada
Pacific over the Fraser River, British
Columbia.
Bridges built after the new design are
known as cantilever bridges. Each
end is made up of a section extending
from the shore nearly half way over the
chasm. Each section is supported
about its center by a strong tower. The
outer arm having no support, and be-
ing subject like the other to the weight
of trains, a counter advantage is given
by the shore arm being anchored or
weighted.
This style of bridge has been adopted
so as to avoid the very great expense
involved in the construction of a sus-
pension bridge. The towers on either
side will rise from the waters edge.
Between them will be a clear span of
500 feet over the river, the longest double
track truss span in the world. The shore
arm of each cantilever having been built
and anchored, the other arm will be
constructed in sections of twenty-five
feet, the whole being made self-sustain-
ing as each section is added.
The ends Of the cantilevers will reach
only 375 feet beyond the towers, leaving
a gap of 125 feet to be filled. The link
will be supplied by an ordinary truss
bridge, which will be swung into place
and rested on the ends of the c%antilevers.
Here provision will be made for expan-
sion and contraction by allowing play
between the ends of the truss bridge
and of the cantilevers. At the same
time the bridge will be thoroughly
braced S as to prevent danger from
the lateral pressure of the wind. The
''wave' motion perceptible on a sus-
pension bridge will not be felt on the
new structure.
The total length of the bridge will be
1915 feet. 1t will have "a double track,
and will be strong enough to bear two
of the heaviest freight trains extending
the entire length of the structure, and
under a side pressure of wind at sew
enty-tive miles per hour, and even then
it is to be strained to only n fifth of
its ultimate strength.
The towers will not rest on bedrock,
as the rush of the river would sweep
away any caissons OF other works in
tended to be used for excavations,
but the foundations will be in the large
boulders that have dropped from the
cliff during past ages, the crevices
being filled in with cement, making q
solid foundation. The pressure will be
SO divided that upon the foundation
rock it will be only twenty-five pounds
to the square inch. The top of the
stone structures will be fifty feet abov
the water level, and from these the
steel towers supporting the cantilevers
will rise 100 feet. From the tower
foundations up the whole bridge will
be of steel, every inch of which will be
subject to the most rigid tests from
the time it leaves the ore to the time it
enters the structure Toledo (CGn.)