Fig. 11: PANYNJ ’s careful monitoring and testing of the main cables and suspender ropes has provided essential information for its planning of the GWB’s biggest maintenance
and replacement project to date. Photo Courtesy of Mario Burger.
Fig. 10: Below the GWB bridge deck, the lower suspension connections of the 2 7/8 inch suspender ropes with the cross beams is an area subject to corrosion from moisture and
road salts. Engineering News-Record, 1931.
ropes, especially where they connect with the roadway, where water and road salts create a corrosive environment. T e ropes have a safe carrying capacity, but it gradually reduces over time, and the replacement project is underway before the safety factor becomes an issue.” As to the design of the replacement ropes, Yostpille said,
“T e confi guration of the 37-wire strands around the center rope provides high capacity resistance to erosion and fatigue. T e strand wires are tightly nested, which minimizes voids and moisture intrusion. T is design is inherently very appropriate, and we will use the same confi guration for the replacement ropes.” “During construction,” Yostpille explained, “A temporary duplicate set of ropes will be methodically staged to take the tension out of the ropes to be replaced. T is work will be monitored with strain gauges and the deck will stay in the same position. T e sequencing of the rope replacement will be left up to the contractor.” T e 296 ropes loop over the main cables and weigh from 1,500 to 10,000 lbs., depending on their length. If laid end-to-end, the ropes would stretch 32 miles. If the 283 wires in each rope were laid end-to-end, they would stretch 9,100 miles, more than 1/3 the circumference around the Earth’s equator. When asked if the replacement ropes will be
manufactured in the U.S., the PANYNJ engineers replied, “Too early to tell.” PANYNJ announced the $1 billion GWB Suspender
Rope Replacement Project last December, to be fi nanced with revenues from its 2011 toll increase, and estimated that it would create 3,600 jobs. T e overall project includes cleaning and rehabilitation of the main cables to address some corrosion and loss of galvanized coating on the wires, work on the cable strands in the anchorages to address some minimal number of broken wires, and installation of a new energy-effi cient LED system for the bridge’s signature necklace lighting (Fig. 12). PANYNJ Commissioners approved $15.5 million for planning and design, and engaged Amman and Whitney, co-founded by Othmar Ammann in 1946, as the consulting engineer for the project. Andrea Giorgi Bocker, the resident engineer in charge
of construction at the GWB, told T e New York Times in December, “T is is a structural engineer’s dream.” Ms. Bocker’s father managed the GWB while she was growing up, and visiting him at the bridge led her to become an engineer. “Suspension ropes aren’t replaced every day,” she said. “In the case of the George Washington Bridge, it’s happening for the fi rst time in its 80 year life. So it’s a once-in-a-lifetime opportunity for an engineer to be part of.” y
WIRE ROPE EXCHANGE
Cliff ord Zink is an industrial
and engineering historian and preservation
consultant, and the author of The Roebling Legacy.
JULY-AUGUST 2012 29
Fig. 12: The GWB Suspender Rope Replacement Project includes installing new suspender ropes that match the original Roebling ropes, cleaning and rehabilitation work on the main cables and the strands in the anchorages, and installation of new energy-effi cient LED
necklace lighting. Photo Courtesy of Mario Burger.
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