Clearfield Republican. [volume] (Clearfield, Pa.) 1851-1937, 1878-05-08

Having been towed out on tho site Of
the intended pier the cylinders were
lowered by hydraulic apparatus till
they rested on the river bottom. Work.
men then descended the internal shafts,
excavated the material from beneath
tho cylinders, and so caused them grad
ually to sink until they reached the rock,
In which a level bed was cut for their
permanent resting place but after the
work had been in progress for some
time II was found that the rock sud.
denly shelvcd away to great depth
under beds Of clay, gravel and sand. 1t
therefore became impracticable to sink
the piers to that foundation, land new
method had TO be introduced. The
weight OF the pier was lightencd by
substituting in the upper works iron
columns for solid brick, while the adop-
tion for each pier of a single oval cyl
inder measuring 233 feet by 139 feet
secured larger bearing than bad pre-
viously been obtained with two small
er ones. The outer casing was OF NAL.
leable instead of cast iron. When the
large masses were prepared they were
fioated out and lowered TO the river
bottom, the sand at the base being re-
moved by pump invented by one Of
tho assistant engineers. By the work.
ing Of the pump large cavity was
speedily formed under the cylinder, and
the huge mass Of metal sank into 1t by
its own weight, reaching to depth Of
about 1S feet below the bed Of the riv-
er The interior Of the cylinder was
afterwards filed TO the top with con-
crete, and the upper part, so far MS II
stood above the bottom of the river,
was next removed, thus leaving an am
pie platform of artificial rock for the
reception of the uper.structure, which
consisted in the first instance of brick
work in the form of an elongated hex
agon measuring 20 feet by 10 feet, and
placed with its greater length in the
direction of the current. This part Of
the pier was likewise put together on
shore and foated out between barges
in q length Of about 20 feet, being suf-
fcient when placed upon the cylinder,
TO reach above low water-mark. From
the low.water level the pier was form
cd OF solid brickwork, built in the or
dinary way by workmen brought along.
side as the state OF the tide would per.
init and at high.water mark four
courses of stone Of an aggregate thick
ness Of four or five feet finished off this
portion of the work The piers Of IA
spans were founded in this way, the
upper works being formed of iron col
umns of ~ and Is inches diameter.
When the piers had been brought to
the necessary height, the grders, meas
uring 245 feet in length and weighing
100 tons for each span, were towed
out and deposited. The raising of the
girders when the piers had been CON-
pleted was carried on in lifts Of 20 feet
at time by hydraulic apparatus.-
Two girders connected by transverse
braces, going TO each span, the depths
varying according TO the width of the
hphco W Dc clOcrtus iuc iohbth va tho
spans diminishes in going toward the
shores, on either side Of the navigable
channel, the depths OF the girders be-
ing correspondingly decreased, the
minimum being IL feet To provide
for expansion by heat, which will
amount to something like seven feet in
tho whole. length OF the bridge, the gir-
dcrs have been adjusted to the piers to
allow certain amount Of free play.
The bridge has been calculated for a
rolling load of Il tons to the foot run.
Such burden is more than could be
brought upon any span by filling its
whole length with loaded freight cars
no part Of the bridge would have to
undergo strain of more than four tons
to the square inch, and when it is borne
in mind that the iron is actually capa-
bic of sustaining strain 2l tons to
the square inch, il will be seen that
there is an ample margin of surplus
strength.