Fig. 7: In 1931 the George Washington Bridge cables nearly
doubled the record main span. Photo courtesy of the NY & NJ Port Authority
“A sudden leap forward into a whole new range of magnitude”
Fig. 6: John A. Roebling’s 1846 Patent Drawing of his traveling wheel
“for the manufacture of Suspension Cables.” Rensselaer Polytechnic Institute, Institute Archives and Special Collections
spanning 800 feet. After serving in the Civil War, his son Washington A. Roebling joined him in completing the Cincinnati Covington Bridge, now called the John A. Roebling Bridge, in 1867 with 121⁄2-inch cables spanning 1,056 feet. Roebling designed the monumental Brooklyn Bridge with four 151⁄2-inch cables and a span of 1,600 feet, but tragically died while surveying for the Brooklyn Tower foundation in 1869. Washington Roebling famously suffered his own injuries while building the Brooklyn Bridge (Fig. 2) and completed it in 1883 with help from his wife, Emily Warren Roebling. John Roebling left his wire rope business, the John A. Roebling’s
Sons Company, to Washington and his brothers Ferdinand and Charles, and over the next 50 years they built it into the nation’s leading manufacturer of wire rope. Te Roebling Company built
the cables on the Williamsburg Bridge in 1903, the Manhattan Bridge in 1909, and the Bear Mountain Bridge in 1924, and it manufactured and installed the suspender ropes for all of these. Te Roebling Company won the Port Authority of New York’s cable
contract for the George Washington Bridge in 1927. Te unprecedented design by Othmar Ammann, the Authority’s Bridge Engineer, presented numerous challenges for building four 36-inch cables spanning 3,500 feet, double the record span. Charles C. Sunderland, Roebling’s Chief Bridge Engineer, called the proposed bridge “a sudden leap forward into a whole new range of magnitude (Fig. 7).” One of Sunderland’s biggest challenges was supporting the 3,500-foot main span of the two footwalks, or scaffolds, needed to build the four great cables. As Engineering News-Record noted in 1930, “No ropes so long as would be required to support these walks had ever been built for such exacting service. It was necessary to stretch these ropes after fabrication to loads in excess of the maximum working load, in order to eliminate erratic or excessive sag.” To solve this problem, Sunderland built a Prestretcher operation
Fig. 5: Replica of John A. Roebling’s first successful wire rope used on the Allegheny Portage Railroad. Manufactured by Loos & Co. of Pomfret Center, Ct., in 2006 to commemorate the bicentennial of Roebling’s birth. Loos & Co.
at the Roebling Company’s Kinkora Works in Roebling, N.J. At the ends of the Prestretcher’s 1,850 feet long track (Fig. 8), hydraulic machines stretched the looped footbridge ropes with 200,000 pounds of tension, 25 percent higher than the required working load of 160,000 pounds. Engineering News-Record in 1930 cited the Roebling Prestretcher as “one of the most important advances made in the suspension bridge
WIRE ROPE EXCHANGE MAY-JUNE 2012 21
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