The Democratic advocate., 1883-08-04
Bridging Niagara.

Work on the foundations OF the Canada
Southern railways great bridge over the
Niagara is steadily progressing. The loca-
tion is at point about three hundred feet
above the present suspension bridge, where
the chasm is $50 feet from bluff to bluff.
The railway company experienced much
difficulty in selecting plans from those pre-
sented, but finally accepted those of the
Central Bridge works of Buffalo. The
contract requires that the bridge be COM
pleted by December 1, 1883, under the
forfeiture of $500 per day for each days
delay after that date. The design selected
is what is known as the canti-lever bridge,
the principle of which is that of a trussed
beam, supported at or near its center, with
the arm extending on each side, and one
end anchored or counterweighted to pro-
vide for an equal loading. 1t is in prac-
tice an entirel y new design, no bridge as
vet having been completed upon this prin-
ciple. The Firth Of Forth bridge in Scot
land, with clear span of 1000 feet, is be-
ing built upon this plan, and in this cOun-
try the Fraser river bridge, 315 feet clean
span, on the Canadian Pacific, is now being
constructed after the same plan.
The bridge is to be double track steel
bridge, being built to carry upon each track
at the same time a freight train of the
heaviest kind, extending the entire length
of the bridge, headed by two "consolida-
ton engines and side pressure of thirty
pounds per square foot, which pressure is
produced by wind having velocity Of
seventy-fve miles per hour. Under the
above loads the structure is strained to only
one-ffth of its ultimate strength. The to-
tai length of the bridge proper is 895 feet,
divided into two canti-levers of 375 feet on
the Canadian and 395 on the American
side, supported on steel towers rising from
the waters edge A fixed span of 125
feet is suspended from and connects the
river arms of canti-levers. The clear span
across the river is 800 feet, being the
longest double track truss span ever built.
The excavations are carried down until
solid rock is reached, when blocks of "Biton
Colguet" twenty feet wide, forty-five feet
long. and ten feet thick, will be put in
These form one single mass that will with
stand a pressure almost equal to the best
Quincy granite, and will so distribute the
load of 1000 tons that comes upon each
pair of steel columns that it will produce a
pressure of but twenty-five pounds per
square inch on the natural formation.
Upon these Biton blocks, four in number,
will be built masonry Of the most substan-
tial character, carried up fifty feet above
the surface of the water. On these the
steel towers rest, rising 130 feet above the
masonry, and upon these will set the steel
superstructures. The material for this will
be objected to the most rigid inspection
and tests from the ore until it enters the
completed structure. For erection at the
bridge site temporary scafolding, using
some 10000 feet Of timber, will be built
on the bluff from either side out to the edge
of the water, on a level with the top of the
bluff Upon these the shore arms Of the
canti-levers will be erected one end resting
on the steel towers and the other upon
masonry on the bluff The shore ends will
be firmly anchored to this masonry, so that
it will take an uplifting force of 400 tons
at each end to displace it. This constitutes
the counter weight to balance the unequal
| loading on the river arm referred to above;
as this, under the most unfavorable condi-
tions can never equal 200 tons, the provi-
sion is ample After the structure is COM
pleted from the shore to the towers comes
the difficult portion of the work-to span
| the 400 feet across and 245 feet above a
roaring river, whose forces no earthly power
can stay, and no temporary structure can
/ survive moment Here the skill of the
engineer comes in to battle nature and
laugh at her powers.
The design of the canti-lever is such that
after the shore arm is completed and an
chored, as described above, the river arm
may then be built out, one panel or section
at time, by means of great travelling der
ricks, and be self-sustaining as it progress
es. After one panel of % feet is built and
has its bracing adjusted, ten travelling der
ricks are moved forward and another panel
erected Thus the work progresses, section
by the section, until the ends of the canti-
lever are reached, when there still remains
a gap of 125 feet to close. Into this will be
! swung anu SuSpeuueu lIOIn CdHIl-leNSI dIHlS
an ordinary truss bridge, forming the con-
Meeting link and completing the structure.
! Compensation for expansion and constrac-
ton is provided for, an ingenious arrange
ment between the ends of the canti-lever
and fixed span, allowing the ends to move
freely as the temperature changes, but, at
the same time preserving perfect rigidity
against the side pressure from the wind,
There will be no guys for this purpose, as
in the suspension bridge, but the structure
will be completed within itself. Neither
will there be any of that wave motion no.
ticed on suspension bridge as train
moves over it. When it is considered that
it took over three years to build the pres
ent suspension bridge, which is for single
track, and that this bridge, for double
track, must be finished within u months
from the execution of the contract, some
idea may be formed of the magnitude of the
operation.
Idleness.