Bridge's main cables made of thousands of wires

The Golden Gate Bridge in San Francisco is supported by two main cables, each made up of 27,572 parallel galvanized steel wires. These cables are essential for holding up the bridge's deck and are among the largest of their kind in the world.

Total wire length exceeds Earth's circumference

The total length of the wires in both cables is approximately 129,000 km (80,000 miles), which is more than three times the circumference of the Earth at the equator. This vast length highlights the scale of the engineering involved in the bridge's construction.

Cable dimensions and structure

Each main cable measures 7,650 feet (2,332 m) in length and 36 3/8 inches (0.92 m) in diameter, including the covering. The cables are composed of many smaller wires, each with a diameter of 0.192 inch (4.88 mm), grouped into 61 strands of an average of 452 wires each.

Efficient wire-laying process

The wires were laid one by one on site by a wheel that made a round trip from one anchoring block to the other, similar to the shuttle of a loom. This process was made more efficient by an auxiliary cable that was stretched with the same curvature as the future main cables.

Wire-laying completed ahead of schedule

The wire laying was completed in 6 months and 9 days, more than 7 months ahead of the contract deadline. The process began in the autumn of 1935 and was completed on May 20, 1936, involving an average of approximately 680 km of wire per day over about 190 days.

Wires sourced from a historic company

The wires were sourced from the John A. Roebling's Sons company in New Jersey, using a method developed in the 1840s. This company later developed a system capable of pulling six wires at once, identified by colors to avoid confusion.

Productivity and efficiency in wire-laying

During an eight-hour shift, the wheels used to lay the wires could pass up to 1,600 km of wire. A second wheel met the first in the middle of the bridge, exchanging wires and doubling productivity, which helped speed up the process significantly.

Final shaping and support of the bridge

Once the 61 strands were in place, jacks tightened the wires to give the cables their round shape. Steel hangers were then passed over these collars to support the deck, ensuring the bridge's stability and strength.

Weight and force of the cables

The total weight of the two cables, hangers, and accessories is 22,200 tons. On each of the two towers, the cables exert 61,500 American tons (56,000 t) of force, demonstrating the immense load they carry.

Historical display and information panel

A full-scale cable cut is displayed at the bridge, showing the 27,572 parallel wires tightly pressed together. A historical panel installed in 2012 at the southern viewpoint provides information about the wire laying process, offering visitors insight into the construction's complexity.

Completion well before the bridge opened

The last wire was laid one year and seven days before the bridge's opening on May 27, 1937, showing the extensive planning and preparation that went into the project.