The Vancouver independent. (Vancouver, W.T. [Wash.]) 1875-1910, 1883-07-05
Bridging Niagara.

ada Southern railways great bridge over
the Niagara is steadily progressing. The
location is at point about three hun
bred feet above the present suspension
bride, where the chasm is $50 feet from
bluff to bluff. The railway company ex.
perienced much difficulty in selecting
plans from those presented, but finally
accepted those of the Central Bridge
works of Buffalo. The contract requires
that the bridge be completed by Decem-
Der 1, 1888, 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 trussed
beam, supported at or near its center,
with the arms extending on each side,
and one end anchored or counter
weighted to provide for an equal loading.
1t is in practice an entirely new design,
no bridge as yet having been completed
upon this principle. The Firth of Forth
bridge in Scotland, with clear span o.
1000 feet. is being built upon this plan,
and in this country the Fraser river
bridge, 315 feet clean span, on the
Canadian Pacific, is now being con-
structed after the same plan.
The bridge is to be adouble track steel
bridge, being built to carry upon each
track at the same time freight train of
the heaviest kind, extending the entire
length of the bridge, headed by two
consolidation" engines and a side
pressure of thirty pounds per square
! foot, which pressure is produced by
wind having a velocity of seventy-fve
miles per hour. Under the above loads
the structure is strained to only One.fifth
of its ultimate strength. The total
length of the bridge proper is S95 feet,
divided into two canti-levers of 375 feet
on the Canadian and 1876 on the Ameri
can 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 500
feet, being the longest double track
truss span ever built. The excavations
reached, when blocks of "Biton Col
guet" twenty feet wide, forty-five feet
long. and ten feet thick, will be put in.
These form one single mass that will
Withstand pressure almost equal to the
best Quincy granite, and will 80 dis
tribute the load of 1000 tons that comes
upon each pair of steel columns that it
will produce 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 substantial charac-
ter, carried up fifty feet above the sur.
face of the water. On these the steel
towers rest, rising 100 feet above the
masonry, and upon these will set the
steel superstructures. The material for
this will be subjected to the most rigid
inspection and tests from the ore until it
enters the completed structure. For
erection at the bridge site temporary
scaffolding, using some soc, 900 feet OF
timber, will be built on the bluff from
either side out to the edge Of the water,
on q level with the top of the blum.
Upon these the shore arms of the can't.
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 masonary,
so that it will take an uplifting force Of
400 tons at each end to displscs it. This
constitutes the counter weight to bal
ance the unequal loading on the river
arm referred to above; as this, under
the most unfavorable conditions can
never equal 200 tons. the provision is
ample. After the structure is completed
from the shore to the towers comes tho
difficult portion of the work-to span the
400 feet across and 245 feet above . roar.
ing river, whose forces NO earthly power
can stay and no temporary structure can
survive q moment. Here the skill OF
the engineer comes in to battle nature
and laugh ut her powers.
The design of the csnti-lever is such
that, after the shore arm il completed
and anchored. ss described above, the
river arm may then be built out, one
panel or section ct time, by means OF
great travelling derricks, and be self-sus-
tanning as it progresses. After one panel
Of IS feel ie built and has its bracing ad-
4 listed. ten travelling derricks are moved
forward and another panel erected. Thus
the work progresses, section by the Sec
ton, until the ends of the canti-lever are
reached, when there still remains . gap
OF 125 feet to close. Into this will be
swung and suspended from the can't
lever arms an ordinary truss bridge,
forming the connecting link and CON-
plotting the structure. Compensation
for expansion and contraction is provided
for an ingenious arrangement between
the ends Of the canti-lever and fixed
span, allowing the ends 70 move freely
- the temperature changes, but, 1t the
same time preserving perfect rigidity
against the sids pressure from The wind.
There will b no guys for this purpose.
a. in The suspension bridge, bat the
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