Green-Mountain freeman. [volume] (Montpelier, Vt.) 1844-1884, 1883-07-25

| The New NIAGARA BRIDGE The
southern railroad bridge over Niagara
river is to be built at point about three
hundred feet above the present suspension
bridge. The contractors have engaged
under very heavy penalty to com plele
the whole by the first of December next,
about eight months from the time OF
beginning operations. The time occupied
in building 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 employ new princi-
pie never before illustrated by any large
work actually finished. Two similar
bridges, however, are now being construct
ed-one. the new Tay bridge over the
Firth of Forth, Scotland, and the second
for the Canadian Pacific railway over the
Fraser river, British Columbia. Bridges
after the new design are known as can't.
lever bridges. Each end is made of II
section extending from the shore nearly
half way over the chasm. Each section is
supported about its center by strong
tower. The outer arm, having no support
and being subject like the other to the
weight of trains, n counter advantage is
given by the shore arm being anchored or
weighted.
This style of bridge has been adopted to
avoid the very great expense involved in
the construction of the suspension bridge.
The towers on either side will rise from
the waters edge. Between them will be
a clear span of five hundred fee over the
river, the longest double 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-sustaining as each section is added.
The ends of the cantilevers will reach only
375 feet beyond the towers. leaving 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 end of the cantilevers. At the same
time the bridge will be thoroughly braced
so as 10 prevent danger from the lateral
pressure of the wind. The wave motion
perceptible on suspension bridge will
not be felt on the new structure. The total
length of the bridge will be S95 feet. Il
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 seventy-fve miles per hour, and
even then it is to be strained to only one.
fifth of its ultimate strength.
The towers will not rest on bed d.rock, as
the rush of the river would sweep away
any caissons or other works intended to
be used for excavations, butthe foundations
will be in the the large bouders that have
dropped from the cliff during the past
ages, the crevices being filled in with Gem.
ent, making solid foundation. The press
ure will be so divided that upon the founda-
lion rocks it will be only twenty. five
pounds per square inch. The top of the
stone structures will be fifty feet above
he water level. and from these the steel
overs supporting the cantievers will
rise 1870 feet. From the tower foundations
up, the whole bridge will be of steel,
avery inch of which will be subject to the
most rigid tests from the time it leaves
he shore 10 the time 1t enters the struc-
ure.