The history of the Golden Gate Bridge

The Golden Gate Bridge opened on May 27, 1937, and has since been standing as a landmark synonym to the city of San Fransisco.

It was constructed between 1933 and 1937 in the Bay Area, and its 8,980 feet (2,737 m) total length is providing a vital link between San Fransisco and what is now Marin County, which had previously been connected via ferry service, since 1820.

The bridge was designed by Joseph Strauss, who was the project’s Chief Engineer, to carry six lanes of traffic and two pedestrian/bicycle lanes.

Strauss had previously submitted a different design for the bridge in 1921, which would be a hybrid solution featuring a suspension span supported by cantilever trusses. This design was ahead of its time and would later be employed in several projects but was rejected at that time as it was considered “ugly”.

Furthermore, it is a suspension bridge, divided into three spans, with the longest middle one measuring roughly 4,200 feet (1.28 km) and its two side ones about 1,125 feet (345 m) each, reaching a total suspension span of 6,450 feet (1,966 m).

It is worth noting that the bridge’s central span held a world record for its length, until it was surpassed by the Verrazzano Narrows Bridge in 1964.

Its impressive deck is supported by two main cables, each being 7,650 ft (2,332 m) long, and 36 3/8 in (0.92 m) thick in diameter and stands 220 ft (67 m) above water.

Both cables rest upon the structure’s two towers, which stand 746 ft (227 m) tall above water and apply a load of 61,500 US tons (56,000 metric tons) per cable on them.

Prior to construction, several aspects of the design were tested. Furthermore, the site’s geology was assessed by Andrew Lawson, who was a consulting geologist, at the point of the south tower, where foundations would reach a depth of 110 ft (34 m) below low mean water level.

The area was primarily consisting of serpentine rock, and a 20-inch square specimen was loaded by the equivalent load of a railway boxcar, where it proved to be of adequate strength.

As for the steel design, the engineers proved their hand calculations by testing a 1:56 scale model, which confirmed by extrapolation that two towers would be able to withstand the load imposed on them by the cables.

Unforeseen circumstances, such as accidents or weather conditions, delayed the bridge’s construction on some occasions. However, it was delivered ahead of time, after four and a half years of construction.

It was also completed below budget, with a total cost of $33.7 million, or $1.3 million less than what was originally estimated. Accounting for inflation, the cost of the bridge would have been $710 million in 2023.

The 66,043-metric-ton structure had to be retrofitted several times, in order to be maintained, ensure its safety, and adjust to the future. Some of these main improvements include:

•  The addition of a lower lateral bracing system between 1953-1954, after a storm in late 1951 threatened the bridge’s structural integrity.

• All the suspender ropes were replaced between 1973-1976, which was the first time such an action was performed on a major suspension span. The need for this replacement was created after a previous inspection discovered corrosion in the elements, while the bridge remained open during all the process but four nights.

•  Earthquake retrofitting took place during 1980-1982 to meet modern standards.

• The deck of the bridge was replaced between 1982 and 1986. Environmental conditions had gotten to the structure’s original steel and concrete deck, which was replaced by a new orthotropic one, again without closing for traffic.

• Seismic retrofitting was again done in two phases between 1997-2008, while a third phase is expected to commence in 2024. These actions came after the 1989 Loma Prieta Earthquake and taking into consideration the area’s high seismicity.

The Golden Gate Bridge was listed by ASCE as one of the Modern Wonders of the World, and it is undoubtedly one of the most remarkable modern engineering structures. Its official website features the bridge’s history and construction details in great detail in case you want to dive deeper into the details.