suspending the brooklyn bridge
DESCRIPTION
Three spread magazine article discussing the process of constructing the Brooklyn Bridge.TRANSCRIPT
Historical Tribute
SUSPENSION BRIDGES MAY DATE BACK TO ANCIENT TIMES, BUT THE FIRST TRULY MODERN SUSPENSION BRIDGE WAS CREATED BY JOHN AUGUSTUS ROEBLING, IN NEW YORK.
Although modern suspension bridges dazzle the eye as awesome feats of technology, the
engineering form is nearly as old as man himself. Vines were the source of cables on the
earliest suspension bridges. In the fourth century A.D. plaited bamboo and iron cables
were used on bridges in India.
The first truly modern suspension bridge was constructed in the mid-nineteenth century
by John Augustus Roebling, a German born American engineer. His bridges, which still
stand, have towers supporting massive cables, tension anchorage for the stays, a roadway
suspended from the main cables, and—a vitally important innovation—a stiffening deck
below of beside the road deck to prevent oscillation. Roebling’s first grand success, was
a bridge with four suspension cables and two decks, that spanned Niagara Falls in 1855.
The determined engineer soon undertook a still more ambitious task: construction of the
Brooklyn Bridge connecting Long Island and downtown Manhattan, a distance of 1,600
feet across the East River.
1866 Legislation passed for construction of New
York-Brooklyn Bridge.
1868-1869
Council approves $1.5 million for the costs of
construction. As surveying nears completion,
Roebling is injured in freak accident. He dies
of tetanus 17 days later. His son, Washington
Roebling becomes project engineer.
1867
John Roebling presents design for 1,600 foot
bridge across East River.
In 1867, Roebling had a revolutionary idea of using steel wire,
more resistant than iron, for the cables. Six iron trusses would
run the length of the bridge’s floor for stability. Aesthetics,
too, were a consideration, as evidenced by the beautiful stays
and broad walkway. Roebling had a tragic accident and died
in 1869, but his son Washington Augustus Roebling assumed
responsibility for the construction, which was not completed
until 1883.
In order to dig the foundations and sink the towers of the Brooklyn Bridge,
Roebling used pneumatic caissons, a method still very in the experimental
stage in his day. A pneumatic caisson is a huge box or cylinder that has
a lower cutting edge, closed at the top and is filled with compressed air
to prevent soil and water from entering. The vessel contains an internal,
airtight deck, with a pressurized chambers below, where workers excavate
the waterbed. Mud, rocks and rubble are hauled out through another air
lock, and concrete is lowered in. The pneumatic caissons today are now
constructed of reinforced concrete; Roebling’s caissons (which measure
approximately 100 by 160 feet) were made of yellow pine, and coated with
pitch on the inside of it, with tin on the outside of it. Furthermore, no one
in the mid-nineteenth century understood the necessity of decompressing
slowly after working in the chamber of the caisson; more than 100 bridge
JOHN ROEBLING HAD A TRAGIC ACCIDENT AND DIED IN 1869. HIS SON, WASHINGTON AUGUSTUS ROEBLING TOOK OVER THE RESPONSIBILITY FOR THE CONSTRUCTION.
Historical Tribute
1 7 2 D E C 2 0 1 0
1870
Construction for the wooden caisson, on
the Brooklyn-side, begins in January. A fire
damages caisson in December.
1871
Construction begins on New York–side
caisson and the construction is completed
on Brooklyn-side caisson.
1872
Washington Roebling is incapacitated by the
“caisson disease,” making him an invalid. He
continues to direct the project with the help
of his wife, Emily.
Roebling himself suffered severe cases of “the bends.”
Today, the length of time one spend underwater and the
rate of decompression are regulated by law.
Roebling’s two pneumatic caissons suffered a series of disasters—
floods, fires, and blowouts—as the cutting edges gradually sank
into the riverbed. Working three shifts of eight hours each for more
than two years, 360 men remove mud and gravel, exploded the
hard clay bottom, and removed trap rock and gneiss—all by the
light of gas burners and calcium lights.
Erecting the cables occupied another twenty–six months. After the
271.5 foot towers were constructed, the first wire connecting the
banks was towed the way across by scow and hoisted into position
between the two towers. A
second rope was dragged
back and the two ends
spliced together, forming
a continuous rope, or
“traveler rope.” On each bank the rope was looped around driving
and guiding wheels attached to the anchorage. (In all suspension
bridges, anchorages secure the ends of the cables and may be
made of masonry, concrete, or natural rock.)
THE CAISSONS SUFFERED A SERIES OF DISASTERS—FLOODS, FIRES, AND BLOWOUTS—AS THE CUTTING EDGES GRADUALLY SANK INTO THE RIVERBED.
1 7 3
Historical Tribute
1875
Construction of New York–side caisson
is completed. The construction of both
anchorages are in process. The towers
are completed on both sides.
1876-1877
Manufacturing of steel–strand cables begins
for bridge.
1878
Small strand in bridge support cable snaps,
leading to an investigation of J. Lloyd Haigh
company, supplier of inferior bridge cables.
A temporary footbridge is opened and the
construction of roadway begins.
Next, other ropes were drawn across and a planked footbridge is built, to
regulate the placement of the cables. Extemely large wheels of wire were
positioned near the anchorages on the Brooklyn side. A loop of two wires
was hung around the light wheels of a “traveling sheave,” which in turn
was fastened to the traveler rope. Thus one trip of the sheave carried two
wires from the Brooklyn to the New York bank, where they were fastened
to a horseshoe-shaped structure called a shoe. The sheave brought two
more wires across. A total of 286 wires, bound parallel, went into each
strand, and nineteen strands, in turn, made up each of the four cables.
The modern method of suspending a suspension bridge, is not all that
different. Although faster and much more efficient. Tower and anchorage
foundations are laid first by underwater excavating, driving piles, the use
of pneumatic caissons, or cofferdam (a wall that isolates the area of work)
depending upon the exact condition of the waterbed. Next, the concrete
pier tops are leveled. Steel slabs nearly 5 inches thick are attached to the
piers with steel dowels, and bottom sections of the towers are welded to
the slabs. Steel platforms, equipped with cranes and other hoisting gear,
are slung between the lower towers, which are gradually built up. Cables
of high-tensile steel, with individual parallel wires or twisted wires, may
be as massive as 1 reels bearing nearly 30 miles apiece, the ends of the
cables being carefully spliced together. A carriage motivated by a pulley
system bears the reel over a fixed cable, from one anchorage.
A TOTAL OF 286 WIRES, BOUND PARALLEL, WENT INTO EACH STRAND, AND NINETEEN STRANDS, IN TURN, MADE UP EACH OF THE FOUR MASSIVE CABLES.
1 7 4 D E C 2 0 1 0
1882
By a narrow 10-7 vote, the bridge company
retains Roebling as project engineer, after a
dispute over delays and cost overruns.
1883
Bridge roadway is completed. Roebling’s
wife, Emily, becomes first person to travel
across completed bridge by carriage. The
bridge opens to traffic on the 24th of May.
President Chester Arthur attends opening
ceremony of the bridge.
1880
J. Lloyd Haigh is imprisoned for fraud. The
road construction continues.
CHORDS OF THE STIFFENING TRUSS ARE ADDED ONLY WHEN THE BRIDGE IS NEARLY COMPLETE. UNTIL THAT TIME IT REMAINS VULNERABLE TO STRONG WINDS.
In order for the construction crew to have access to cables, a temporary catwalk of cross-
timbers is erected. Another machine binds the cables together with wire. Finally, a coat
of corrosion-resistant paint is added. All of this to insure the stablilty and longevity of the
suspention bridge.
The road deck is built out gradually from both sides of the river. Or sections of it that may be
floated out and raised into place. There is always a certain degree of distortion, so chords
of the stiffening truss are added only when the bridge in nearly completed. Until that time it
remains vulnerable to strong winds.
The main span (the length between the two towers) of the Verrazano-Narrows Bridge,
connecting Staten Island and Brooklyn, New York, reaches 4,260 feet—the longest in the
world—and the beautiful Golden Gate Bridge in San Francisco stretches a total of 8,981
feet, with a main span of 4,200 feet. The bridge that is the strongest is, New York’s George
Washington Bridge, designed by P. H. Ammann and constructed in 1931. Each of the four
original cables, 1 yard in diameter, containing 26,474 galvanized steel wires, giving a live
load strength of 5,080 pounds per foot. A second road deck was added in 1962, and the
bridge now accommodates fourteen lanes of traffic.
1 7 5