Main Cables and "the Ropes"
Main Cables and "the Ropes"

8,816 zinc coated steel wire, each a little thinner than a pencil (0.196-inch diameter) were "air-spun" into 19 strands to form each main cable. These strands were then hydraulically compacted into a 20-1/2-inch diameter cable cross section, and outfitted with cast steel cable bands to hold the compacted shape and to receive the vertical suspender ropes.



Each main cable wire loops around one of 19 strand shoes held back to the mass concrete foundation of the anchorages with 4?-inch diameter high strength steel threaded anchor rods. Two anchor rods per strand shoe pass through steel pipe grout tubes, and their nuts bear against an anchor frame at the rear face of the anchorage. Once the full weight of the bridge is bearing on the cables, the steel pipes will be filled with grout to protect the 60-foot length of rod from corrosion.



In addition to the cable bands, which hold suspenders at their proper position along the main cables, there is a unique cast steel fitting at mid-span to secure the cables and deck in the same relative position, thus sharing the burden from longitudinal and transverse displacements of the stiffening truss. This feature, referred to as a center tie, is framed into outrigger struts on the sides of the deck and thus tied into the stiffening truss framing. Since the loads transferred are sizable, the number of bolts necessary to provide adequate clamping force to the main cable required a three-part articulated cable band casting with a total length over 21 feet.



The vertical suspender ropes are 1-5/8- or 1-7/8-inch zinc coated steel wire rope often referred to as Bridge Rope. Typically the suspender ropes loop over the cable bands; however, near the anchorages they are pinned both top and bottom to allow relative rotation as the bridge expands and contracts, and to aid construction. To further mitigate the potential for bending fatigue in the ropes, the suspender brackets nearer the anchorages are located at the bottom chord of the stiffening truss. This maximizes the effective length and minimizes the rotation experienced. Excessive rotation for shorter ropes has been the cause of long-term wire breaks in older suspension bridges, and the arrangement selected overcomes the undesirable situation. http://www.grandvan-steel-wire.com/