Outside of the engineering world, most people probably have never heard the term “wire rope.” After perfecting the skill of making ropes in ancient times, it went virtually unaltered for nearly 2000 years. In the 19th-century, hemp ropes and iron chains were for hoisting; the disadvantage was the proverbial weak link. The mining sector required that ropes be made longer, and stronger by drawing iron into thin rods or “wire.” Eventually, steel replaced iron as the preferred building material. The next step was to introduce multi-layer strands made of steel.
Just like natural ropes, “wire ropes” are made by twisting multiple strands of steel into a helix to form a composite rope. The difference between ropes and cables is the overall diameter. Cables are small diameter, single-bundle wires; ropes are large diameter, multi-bundle wires. When laid in a straight, parallel fashion, they are also referred to as a “cable,” regardless of width.
The Golden Gate Bridge has 250 pairs of vertical suspender ropes that are spaced 50 feet apart on the main cable. John A. Roebling’s Sons Company manufactured both the main cable and the suspender ropes for the Golden Gate Bridge. Each suspender rope is 2 11/16 inches in diameter. Due to corrosion where the suspender ropes attached to the roadway, all of the ropes needed replacement. Between 1972 and 1976, the Golden Gate Bridge underwent a complete change-out with the final replacement made on May 4, 1976. The majority of original ropes went to steel salvage, the Bridge District saved some for testing and emergency repairs, and a small portion reserved for commercial use as souvenirs.
In 2016, we joined Strands of History, which was owned by a long-time friend who had acquired the original Golden Gate Bridge suspender ropes. Sadly, our friend and business partner passed away, and in early 2018, we re-launched the business in Lake Tahoe. Our first task was to improve the fabrication methods to clean, bind, cut, polish, and paint the historic steel ropes. Once we accomplished this, we turned our attention to branching out into artistic designs like furniture and art.
Each suspender rope is first sandblasted to remove any remaining layers of debris or paint. After cleaning, a custom hydraulic press exerts 7000 psi to secure stainless-steel bands where cutting is to take place. Although these ropes are over 80 years old, they will still unwind unless controlled by these crimped bands. We use a specially designed chop-saw and 14-inch blades to cut through the stainless-steel bands and steel ropes. Band saws, high-pressure water jets, or plasma cutters don’t work on the suspender ropes because the individual wires vibrate too much; it would be like trying to cut a bundle of toothpicks with a hand saw.
After cutting, the ends are ground and polished to reveal the unique lay and beauty of the 229 individual wires. Below are figures to illustrate the identifying lay of the suspender ropes from the George Washington Bridge and the Golden Gate Bridge. Both bridges were built using suspender ropes manufactured by the John A. Roebling’s Sons Company (as was the Brooklyn Bridge, but we haven’t located that diagram yet).
U.S. Steel manufactured the replacement suspender ropes for the Golden Gate Bridge. The design based on new structural requirements, therefore they have a different lay compared to the original ropes. The unique, signature lay of the wire ropes guarantees that you have the original Golden Gate Bridge suspender rope.
|Wire Lay of The George Washington Bridge Original Suspender Rope
||Wire Lay of The Golden Gate Bridge Original Suspender Rope
||Wire Lay of The Golden Gate Bridge Replacement Suspender Rope
|Built by John A. Roebling’s Sons. Co
2 7/8-inch diameter
Bridge construction 1927 to 1931
|Built by John A. Roebling’s Sons. Co
2 11/16-inch diameter
Bridge construction 1933 to 1937
|Built by U.S. Steel
2 3/4-inch diameter
Replacement period 1973 to 1976