Man has been building suspension bridges for at least 2, 000 years; the earliest recorded example going back to 65 a.d. in china. throughout the centuries, the main tension elements have evolved from primitive organic rope materials to iron chain, eyebars, and finally, wire. since the first iron-wire cable suspension bridge (built in 1816 at fairmount, pennsylvania), the materials, design, and construction procedures have been refined to today's state of the art. we are still learning how well our design and construction methods for these structures will stand up over time. recent in-depth inspections of three of new york's major suspension bridges have provided valuable information to compare the effects of variations of materials andconstruction details on the durability of parallel wire cables. thebrooklyn bridge, possessor of the world's first steel wire cables, is now undergoing rehabilitation that will allow it to continue in service for its second century. the williamsburg bridge, which narrowly escaped demolition after a recent study to determine its fate, will have its cabes cleaned, oiled, and rewrapped at an estimated costof more than 60 million dollars. the mid-hudson bridge, youngest ofthe three, will undergo a detailed study and testing program after strong evidence of stress corrosion cracking was found during a 1987inspection and confirmed by observations made by steinman engineersin 1989. this paper appears in transportation research record no. 1290, third bridge engineering conference, march 10-13, 1991, denver, colorado, volume 1.
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