Activate Javascript or update your browser for the full Digital Library experience.
Previous Page
–
Next Page
OCR
A TWISTORY OF THE BRIDGE. 5
‘in New York, on Chatham Street, opposite the. City Hall.
Rising from the towers at an elevation of 118 feet above
This line and terminus were fixed upon as the result of Mr. | high-water mark in gentle but graceful curve to the centre of
aie S it
gbeel ‘ LENS PNT
Sse = T =
s/f
Roark, Fulton St.
.
. SITUATION PLAN OF BROOKLYN APPROACH.
Roebling’s exhaustive examination and discussion of the question
in his first report, of September 1, 1867, and no reason has been
found to modify or to question the wisdom of his conclusions.
This line strikes the river at its eastern or Brooklyn shore
close alongside of the north slip of Fulton Ferry. Its course
across the river is not exactly at right angles to the shore, but
makes a little down stream, striking the New York side at the
foot of Roosevelt Street—four blocks further up stream, how-
ever, than the still more oblique ferry
the river span, where it meets the cables at an elevation
of 135 feet above high-water mark, is the bridge floor,
an immense steel frame-work bewildering in its com-
plexity. The frame-work consists essentially of two
systems of girders at right angles to each other. The
principal cross-beams or girders supporting the floor
proper are light trusses thirty-three inches deep, placed
seven feet six inches apart, and to these are attached the
four steel rope suspenders from the cables. Half-way
between these principal floor beams are lighter ones, to
give additional support to the planking. To unite these cross-
beams together, and to give the proper amount of stiffness and
strength to the floor, there are six parallel trusses extending
along’ the entire length of the bridge. The floor beams are
farther united together by small longitudinal trusses extending
from one to the other, which, together with a complete sys-
tem of diagonal braces or stays, form a longitudinal truss of
86 feet in breadth. It will thus be seen that this combina-
route. Here, then, are four points de-
&
&
a
J
fined in a straight line: the two ends, and Z Foot bridge R, Foot bridge B: eZ
the two points at the water line, 15954 17 Cable Cable Z
fect apart, to be connected by the bridge
Si
Bridge —2™ Ro,
+- =
proper with a single span. Three points
in the air line of the bridge are also de-
termined: the central altitude of 135 feet
above mean high water required by the
United States government, and the two
terminal elevations, in. New York ‘and
Brooklyn respectively, 38.27 and 61.32 . .
feet above high-water mark.’ The rise from these two to the | tion has immense strength, weight, and stiffness, laterally,
central altitude gives the line of the bridge a gentle upward | vertically, and in every direction.’ To relieve the cables in a
curve from either end. to the centre, where it will be fifteen | great measure of this enormous burden, and at the same time
feet higher than at the towers, and forty-six feet higher than | effectually prevent any vertical oscillations in the bridge floor,
at the anchorages, = SS there is a multitude of suspensory stays of steel wire ropes
The adoption of a suspended span of 15953 fect, at a height | diverging from the tops of the towers to points about 15 feet
of 135 feet, also determined (in combination with other math- | apart along the bottom of four of the vertical trusses. These
ematical and mechanical considerations) the height of the tow- | stays extend out for a distance of 400 feet from the towers,
Ly . 3 and are of themselves capable of sus-
? e 4 taining unaided that portion of the
fas mh CT erent tn |
fSS La S pee] 4 ;
CB: great frame and its load in position.
New Frank Hort Stat "7
100 fr. Dock
g
fs
335-1)
Z es
2
LF 7)
At the towers the frame-work is firm-
13] I=
[eer 2
= J ]knchorate: whe fe Pe :
EE Serge i ; Be os ae ly anchored down, and again confined
Ki 4d pS \VELO#R Boek
| W 7 3 \ #& against the lifting or pushing force of
% iz = oe > > 5S 4
My \F\ - 4] (7/ the wind by a system of under-stays
! lying in the plane of the floor, so that
no conceivable cause can ever disturb
its rigid fixity of: position and form.
ers (2763 feet) from which the span must be suspended, and| At and near the centre of the span, however, where. these
two other points in the air line of the bridge, at which the | stays do not act so efficiently against any tendency to dis-
ends of the suspension cables are secured—in other words, the | tortion, and to ‘still farther unite and’ stiffen. the whole sys-
anchorages—for the cables are not to pull on the tops of the | tem, the two outside cables. are drawn inward ,toward: each
tall towers, but to rest on them with nearly a simple vertical | other at the bottom of. their curves. By this means cach of
pressure, being not even fastened; and thus, so far from tend- | them presents its weight, in the form. of an arch against an
ing to pull the towers over, the suspended weight tends only | oblique pressure from. below. and the opposite side, and resists
to hold them in position. The cables are therefore anchored | more or less in the same way any force from the like direc-
inland, at a distance of 930 feet back from the towers on each | tions. The two inner cables at the same time are drawn apart
side. oo
The anchorages are solid cubical struct-
ures of stone masonry, measuring 119 by
132 feet at the base, and rising some 90
fect above high-water mark. Their weight
is about 60,000 tons each, which is utilized
to resist the pull of the cables. The mode. ,
of anchoring the cables will be described in its proper place. | at the bottom of their curves, thus approaching each its out-
Suffice it for the present to conceive them thus anchored by | side neighbor, and pairing with it, so as to combine their op-
their extremitics on cach side the river 930 feet back from the | posing arches against lateral forces from either direction. The
towers, and at the water-line on cach side lifted up with a long, | weight of the whole suspended structure (central span), cables
lofty, and graceful sweep over the top of a tower 276 feet | and all, is 6740 tons, and the maximum weight with which the
high, and drooping between the two towers in a majestic curve | bridge can be crowded by freely moving passengers, vehicles,
which one can liken to nothing else for grandcur but the in- | and cars is estimated at 1380 tons, making a total weight
verted arch of the rainbow. — ‘| borne by the cables and stays of 8120 tons, in the proportion
SITUATION PLAN OF NEW YORK APPROACH.
[Cable Catite
“| [===
si
b
g
[: Si
=
|
[Gable cae op — ee
a -------— Horizontal wind braces beneath bridge
HORIZONTAL PROJECTION USED IN CABLE SYSTEM.