The Abilene reflector. [volume] (Abilene, Kan.) 1883-1888, 1883-12-27
Cantilever Bridges.

The country. Il see that the new bridge
across the Niagara River, to connect
he New York Central and the Canada
Southern Railroads, will be the first
bridge of that style built in America -
THAT is true was the reply. 'But
first YOU ask me what a cantilever is.
We borrow the term from architecture;
/: means bracket used to support a
balcony, etc. Now, in a cantilever
bridge there are two brackets opposite
each other, each resting Ona pier. The
shore ends of the brackets rest upon
and are fastened down TO another pier;
The outer ends, projecting over the
water. sustain a central span, merely
resting upon them and free to respond
20 the changes in the temperature. To
get a rude idea of the principle of the
cantilever bridge, place two chairs two
feet apart: put a foot-rule on each chair,
held down by a book; the ends of the
rules will rot meet across the space
separating the two chairs, but by rest
ny q third rule upon their ends the
bridge is complete. This is skeleton
idea. Now, in place of the chairs SUBJ
stitute four piers of masonry; instead OF
the two rules, balance upon the piers
two beams resting upon the intermedi.
ate piers and with the shore ends of the
beams placed upon and fastened to the
two extreme piers; another span resting
upon their outer ends substituted for
The third rule, and this is the cantileveI
bridge.
1.-The shore arm of the cantilever OF
bracket rests. aS | have said, upon a
second pier, built back of the first one
at the rivers brink. If there was nc
such support any weight-like that of
a railroad train-if placed upon the
shore arm, would depress it toward the
ground and correspondingly elevate the
outer or stream end. 1t would be as
if, after perfectly balancing plank on
a log. you should place a weight at
one end of the plank. But this is not
enough. Suppose the railroad train
had passed under the tower over the
main pier out upon the outer end of the
cantilever or balanced beam; the extra
weight would depress the outer end and
at the same time elevate the inner or
shore end. So the shore end not only
rests upon a support of masonry, but is
fastened to it, to prevent the train from
tipping the beam up into the air and
falling into the stream"
"What are the advantages claimed for
the cantilever BRIDGE" asked reporter.
For bridges having long spans the
system is asserted to be the most eco
nomical Less material need be used
TO secure the same strength, rigidity and
stiffness than in a suspension bridge, for
instance Less false work or scaffold-
inc is needed for the erection of can
tjlever bridge than for any other braced
structure. thereby making it capable Of
construction with more ease and less
danger of disaster and with no obStrUc-
ton to navigation. The central span
resting upon the outer or stream ends
of the two brackets can freely expand
with the heat of summer and contract
with the cold weather. One end of
this central span is fastened to one of
the brackets, the other end being
placed upon rollers. The detection
from the horizontal under the full load
of the bridge is not half so
great as it would be in a suspension
bridge of the same length of span.
"By explaining, in a general way,
the process of constructing a bracket
or cantilever bridge, you will be able tC
see the economy and ease of the work.
We will start with one iron tower built
upon a pier of masonry, on the east
shore of a stream. The first panel of
the bridge is swung into place for the
Of 40 at foc 81
to the iron tower. A timber support
for each panel as it is put into place is
all the false work required in building
the shore end. As soon as two of
these panels are built, by means of a
derrick the first panel of the stream
arm can be tied to the tower The ex-
ira weight of the two panels for the
shore end of the bracket will fully sUlS-
tain the single panel that is built out in
the opposite direction over the water.
With this done, that panel itself sup
next one can be placed in position and
bolted TO the first panel. In this way
panel by panel can be advanced until
the outer or stream arm of the canti-
lever is completed. Meantime, by
keeping the work on the shore arm in
advance of that on the outer arm, the
weight of the latter will not overbal-
ance the former, which, when COM
pleted. can be placed upon the second
pier and anchored. On the west (the
shore of the stream, mean
time, the other bracket or cantilever is
being constructed in the same way.
Roughly to illustrate the idea, take a
sheet of paper and draw two rs
on the same horizontal line,
leaving little space between them.
The two perpendicular strokes repre-
sent the piers on the respective shores
of the stream. The two horizontal
strokes on the top of the perpendicular
lines represent the two cantilevers OF
brackets. Make two downward per-
pendicular strokes, one from the right
hand end and the other from the left
hand end of the tops of the right-hand
md the left-hand L respectively; these
represent the anchorage of the shore
ends of the cantilevers. Now your
bridge is complete, except the placing
If the central span-to pursue our il
ustration, the drawing of line to con-
lect the two free ends of the rs. This
S done by running wooden truss into
he intervening space certain dis
ance; by means of derrick fastening
,ables to the projecting ends of the !
russ from the end of the opposite can
.ilever; then, by pushing and pulling,
he truss is gotten entirely across the
space. 1t furnishes then the scafold- |
ng or false work needed for placing
he iron work which will make the span |
complete from tower to tower. The /
'nly false work needed. as you see. are
he wooden truss for building the GEN.
raj span and the supporting timbers /