Iowa County democrat. [volume] (Mineral Point, Wis.) 1877-1938, 1880-01-09
THh TAY BRIDGE.
Full Description or the Inflated Struc.
furN

railway bridge over the river lay, near
Dundee, Scotland, full accounts Of
which appeared in cur telesaphic col
umns, gives to the structure itself, u
mourntn interest which must be height
ened by the peculiar nature OF the acct.
dent. From the published accounts
nothing more has been learned than
that vast section Of the bridge has ab.
solutelv disappeared and with il the
passing train, loaded with human
freight, but rs yet there has been no
specific statement rs To the precise
cause ii tho accident, All that isl
known is That the ;raiu lett one end ol
the bridge and brought up at TITO bot.
tom OF the nver. Whether the hr,lse
gave way under the weight OF the tram,
or whether there WAS actually n break,
caused by the prevailing storm, exist.
ing Mt the time the train started across,
vet temMns ~ mere conjecture.
The following description of this fatal
bridge IL taken from the Chicago Times
Commencing NJ the south shore the
bridge, for the first five spans, il ON 4
curve OF quarter of n mile radius, IL
is then straight for n mile and " half,
At the north shore, between high and
low water marks, it describes n curve of
quarter of mile radius, forming
nearly n quarter " u circle near the
town ot DundoA
The level of The rails at the south end
Of the bridge is seventy eight feet above
high water. The gradient doscends one
ia one hundred for the first three spans;
il is level for the next two spans; it then
ascends one to three hundred and
| hity.three toward the centre of the
bridge. over the navigable part OF the
river it is level, and the rails are ninety
two feet above high water, leaving
eighty. eight feet for the passage OF
shipping above high water OF spring
tides. From this the gradient falls ono
in seventy-throe ana ono.half to the
end Of the bridge.
The magnitude Of the several spans
in order. commencing on the File
shore, is M follows: Three spans OF
sixty feet, two of eighty feet, ten of ono
hundred and twoaty feet, twelve OF one
hundred and thirty-six feet, thirteen of
two hundred and thirty feet, one of
one hundred aud tiily-ie0t, eleven OF
one hundred and twenty feet, twenty
1--WE OF sixty feet, one OF one hundred
and hflv.tive feet, and six of twenty
seven feet, the total number OF spans
being eighty.four, and the length of the
bridge three thousand four hundred and
twenty yards.
The first fourteen piers are founded
upon rock, which was generally cover
I'd to the depth of II few feet with clay
or other soft material. These piers
consist of double solid cylinders OF brick
work, built with strong Portland oe-
mcnt mortar, connected by II wall OF
brickwork from low water To the super.
structure. Between the fourteenth and
fifteenth piers the rock disappears. AT
the sites of the next six piers the bed
consists of layer of hard material rest
ing ON silt. These piers were piled
from an outside staging within an oval
shaped wrought.iron calsson. After the
piles were driven, their heads were sur
rounded with concrete, the water was
then pumped out Of the cnlsson and
. brickwork was built M u five feet
above high water. The upper piers OF
these, and of all the piers to the north
VI Iuflit IpllclNN w 'f1'A 1iibli
bracel together. From the twenty
second pier northward the bed OF the
river consists of sand with occasional
layers oil coarse gravel and boulders. IL
was, however, necessary to modify the
design for the piers and the method Of
founding and building them, according
10 the load each had TO carry.
For the ono hundred and twenty and
one hundred and thirty.six feet spans,
there ARE eighteen piers. For each pier
two wrought iron caissons were prepar-
ed, partly cylindrical and partly conical
m shape, and having n base of fifteen
feet These were built on the fore shore,
and lined with brick work; they were
then tl0aied out by means OF pGntoons,
having hydraulic machinery Tor lower.
ing, when they had sunk in their proper
places until they took u bearing IN the
sands the pontoons were removed, and,
by means of sand-pumps, the material
from the interior was removed, and they
sank by their own weight. During the
operation of sinking, rings OF wrought
IRON and brick work were added to the
top of tho caisson, and stones were laid
around tho outside 10 fiji the void caused
by the seoul and pumping. When a
sufficient depth was obtained the pumps
were removed, and the interior WIS filled
with liquid concrete, and when this had
solidiied, the brick work wits eontin-
ued TO above high water.
For the two hundred and thirty feet
spans, large rough.iron caissons Of a
cylindrical form, thirty.one feet in di
ameter, were erected on the foreshore,
one for each pier, and lined with brick
work to the height TO which they were
sank in the sand. the upper and tenn.
porary portion Of the caisson, Of the
same diameter rs the under, but nc
lining Of brickwork was placed on the
top of the lower part and boted secure
ly TO il. The compound oaisson wa
floated ont and sunk NJ above described
by means Of sand pumps, and the per
manent portion Of the caisson WAS fill
ed with concrete. The temporary was
unbolted by divers, and removed for
further nse. From the surface Of the
ground 10 above low water, the pier
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