THE SAS MAIN CABLE
Although there appears to be two cables, the SAS has only one. The single main cable, and the fact that the span itself is asymmetric (the span is longer on the eastern side of the single tower than it is on the western side) gives the bridge its dramatic and dynamic appearance.
The SAS’s single, nearly 1-mile-long cable is anchored into the east end of the roadway, traveling up and over the single tower to wrap around the west end before traveling back up and over the tower to anchor back into the east end; in other words, the 2.6-foot-diameter cable acts like a giant, unbelievably strong sling; the cable’s diameter is also the largest for a self-anchored suspension span. The nearly mile-long cable is also the longest looped suspension cable in any bridge. The cable features 118 miles of 2 1/2-inch steel strands and more than 17,000 5mm wires, each of which can support the weight of a military grade Hummer. The cable is comprised of 137 steel wire strands, each of which contains 127 steel wires. The cable weighs 5,291 tons or nearly 10.6 million pounds.
In late 2011, workers erected a temporary footbridge that travels the path of the SAS cable, so ironworkers have unfettered if precarious access to the cable. On April 5, 2012, crews installed the last of the 137 steel wire strand using a hauling system to pull the coiled strand from the east end of the span over the tower and down to the west end where it loops around before heading back in the same path to anchor into the east end. The state-of-the-art hauling system– designed specifically for this operation allowed workers to complete the unprecedented work of placing the 137 individual strands. Workers placed the first strand on December 19, 2011.
The 137 strands were connected to anchor rods that lock them into place inside the east ends of the road decks, in a space called splay chambers, where the strands transition from being tightly compacted to spreading out to be individually anchored.
The next phase - compaction - began in April 2012 and was completed in May. Four compactor machines compressed the nearly 1-mile-long strands together with pressures up to 9,350 psi (pounds per square inch).
Each steel compactor machine contains six hydraulic jacks and weighs 30,000 pounds. The hexagon-shaped compactors are 2.3 meters (7.7 feet) in diameter and .8 meters (2.6 feet) wide.
The compaction process began at the top of the 525-foot-tall SAS tower with the machines moving 1.5 meters (4.9 feet) at a time. Once compressed to a precise diameter, temporary stainless steel seizing bands are then placed around the cable at 1.5 meter intervals to hold it in place. The strands are also compacted between the jacking and deviation saddles as the strands pass around the western end of the span. The cable is not compacted at the top of the tower as the individual strands pass through a cable saddle.
The custom-made compactors were designed by American Bridge/Fluor (a Joint Venture), the prime contractor building the SAS. The compactors were built by Jesse Engineering of Tacoma, Wash., with the jacks supplied by Enerpac of Menomonee Falls, Wis.
After compaction, workers attached the 114 cable bands to the main cable; crews used cranes and winches to lift the bands into position along the main cable. Fabricated by Goodwin Steel Castings, in Stoke-on-Trent, England, the steel bands range in size from 2.4 to 9-feet-long; the average band is 3.2-feet-long and weighs approximately 1-ton.
Once the first bands were bolted into place on the cable, workers began attaching the suspender ropes that play an essential role in load transfer. The 200 steel suspender ropes, spread amongst 100 of the cable bands, were made by Wireco in Chilicothe, Mo.; 14 of the cable bands help compress and shape the main cable but do not carry suspender ropes.
The steel wire ropes range in length from 16 to 656 feet and vary in weight from 250 pounds to more than seven tons. Despite the varying lengths and weights, the ropes are either 2.8 or 3.5 inches thick; the slightly thinner ropes can hold more than 1 million pounds, while the slightly thicker ropes can carry a weight of 1.5 million pounds. The ropes are hoisted into position over the cable bands using cranes and winches.
- Length of main cable: .86 miles/4,550 feet/1,387 meters
- Diameter of main cable: 31.2 inches 0.79 (meter)
- Weight of main cable: 10.6 million pounds (5,291 tons)
- Number of individual wires: 17,399
- Number of strands: 137
- Number of wires/strand: 127
- Diameter of each wire: 5mm