EoW March 2012

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EuroWire – March 2012 34
The GeorgeWashington Bridge
The daunting task of cleaning the main
cables and repairing the vertical suspender
ropes on the world’s busiest vehicular bridge
A thorough overhaul of the civil engineering marvel that
spans the Hudson River just north of New York Harbour is long
overdue. O cials of the Port Authority of New York and New
Jersey say that comparable bridges normally have their wires
replaced after 70 years or so. At 80, the George Washington is
showing its age, and – after a $4.5 million, two-year study – the
PA in December decided that action could not be postponed.
The agency’s board authorised a rst instalment of $15.5 million
on the estimated $1 billion-plus cost of a renovation that will
create an estimated 3,600 jobs.
Christine Haughney, who covers transportation for the New
York Times, observed that the task of cleaning the four main
cables of the bridge and replacing its 592 vertical suspender
ropes is “daunting in its magnitude.” No more than three of
the suspender ropes that stretch from the main cables to the
roadway can be replaced at the same time. To attempt any more
could destabilise the span.
O cials of the PA emphasised that the 14-lane double-decker
bridge is in no danger of collapsing from suspender
deterioration. But waiting for a safety issue to develop would
involve emergency repairs, and any driver who has experienced
a tra c jam on “the George” will shrink from the prospect of
a closed-o lane. (“At 80, George Washington Needs Bridge
Equivalent of Hip Replacement,” 8th December). The suspender
ropes – which weigh 1,500 to 10,000 pounds each, depending
on length – have never been replaced, but the procedure is
expected to be similar to the “seismic retro tting” of the Golden
Gate Bridge, in San Francisco. Ms Haughney wrote: “For that
project, a rolling platform, known as a traveller, was placed atop
the main cables, and then workers replaced the ropes, using
temporary suspenders, jacking frames and jacks.”
Details on the George Washington Bridge, provided by the
Times include the following:
† If placed end-to-end, the suspender ropes would be
32 miles long. The 283 wires in each suspender rope, if
laid end-to-end, would be 9,100 miles long – more than
one-third the circumference of the earth;
† The wires were a worry-point for the bridge builders in the
1920s, according to Jameson W Doig, a research professor
at Dartmouth College and the author of Empire on the
Hudson, which chronicles the history of the Port Authority.
He said that the bridge’s chief engineer, Othmar Ammann,
at one point considered using eyebars instead of wire
rope. The governor of New Jersey, Arthur Moore, pressured
Mr Ammann to use wire rope because doing so would create
jobs in the state.
“It was a jobs issue,” Dr Doig said. Mr Ammann reserved a
nal decision until he was able to complete an engineering
analysis, whereupon he chose wire and placed the order
with the Roebling Company. The New Jersey-based rm was
run by the descendants of John A Roebling, who designed
the Brooklyn Bridge.
† Vast quantities of wire had gone into the George
Washington by the time it opened, in 1931. Andrea Giorgi
Bocker, the Port Authority’s resident engineer in charge of
construction at the bridge, told the Times ’s Ms Haughney
that the work of twisting 26,474 tightly coiled wires into four
main cables occupied a full year.
In our own era, replacing the suspension wire in stages will
take eight years. In 2013 the PA will commence cleaning up
the massive anchorages tying down the bridge’s foundation,
replacing wires in the cables, and installing new dehumidi ers
in the chambers where the anchors are held.Workers will clean
the main cables by scraping o their zinc-paste wrapping and
introducing dehumidi er. They then will focus on the less stable
parts, replacing the suspender ropes that are spaced at 60-foot
intervals along the 4,760ft bridge.
† “This is a structural engineer’s dream,” Mrs Bocker, whose
father managed the George Washington Bridge when
she was growing up, told the Times. “Suspension ropes
aren’t replaced every day. In the case of the George
Washington Bridge, it’s happening for the rst time. So it’s
a once-in-a-lifetime opportunity for an engineer to be a
part of.”
Port Authority o cials said they will pay for the repairs with
revenue from tolls and fares.
The Detroit Auto Show
Amid a bonanza of emergent engineering
trends, the US industry manifests a new and
‘decidedly globalist’ attitude
An important change in emphasis at the North American
International Auto Show, held 14th -22nd January in Detroit, was
Transatlantic Cable
Image: www.bigstockphoto.com Photographer Zsolt Ercsel