Miracle Bridge Endures

Lifestyles

In many famous science fiction and disaster movies, the Golden Gate Bridge has always managed to escape destruction. Is it because the bridge is fragile? Quite the opposite. The filmmakers deliberately destroy the bridge to emphasize the severity of the disaster. So, how has this remarkable suspension bridge stood tall for nearly 86 years since its construction?

The Golden Gate Bridge connects the city of San Francisco with California, spanning the Golden Gate Channel, which is 2.7 kilometers wide and often experiences gusts of up to 96 kilometers per hour. Traditional bridges with multiple piers would hinder the passage of ships downstream and increase project costs due to the 90-meter water depth of the strait.

To overcome these challenges, engineers explored alternative designs such as arch bridges. However, the need to maintain clearance for ships required an exceptionally high middle arch, which was not feasible with the technology available at that time.

The engineers then turned to the idea of a suspension bridge, which required fewer piers and a simpler structure. The concept was to connect massive steel cables to each end of the bridge, with a secondary cable supporting the bridge deck.

While the idea was promising, ensuring the long-term stability of the suspension bridge presented a considerable challenge. The engineers devised a solution by constructing two tall towers at either end of the strait and connecting them with a parabolic-shaped main cable. Secondary cables were used to link the main cable and the concrete bridge deck.

However, this construction approach introduced a serious flaw: the inward collapse of the tower ends under stress. This issue was resolved by applying tension in the opposite direction, securing the main cable to the ground through an anchoring system.

The main cable of the Golden Gate Bridge consists of 27,572 steel wires, spanning a total length of 129,000 kilometers. From a distance, it appears as a massive steel column—a testament to the engineers' ingenuity. To reduce costs, the engineers decreased the distance between the two towers to 1.2 kilometers, thereby reducing the pressure on the main cable. The diameter of the cable was also reduced to 0.92 meters, significantly reducing construction expenses.

However, these measures alone were not sufficient to ensure the stability of the Golden Gate Bridge. The connection between the sub-cables and concrete posed a potential risk of bridge deck damage and collapse. To overcome this, the engineers replaced the main body of the bridge deck with a steel structure, connecting it to the sub-cables.

Yet, a new challenge arose—thermal expansion. Concrete expands with rising temperatures, causing cracks in the bridge deck and leading to the expansion of the towers. To address this issue, the bridge deck was divided into seven separate sections, connected by steel channels in the expansion structure.

The steel troughs expand and contract up to a distance of over 1 meter, allowing for the bridge deck to withstand thermal expansion without collapsing. Additionally, miniature expansion structures were integrated into the bridge deck every 15 meters, ensuring stability regardless of the season.

The Golden Gate Bridge stands as a testament to civil engineering, overcoming challenging construction environments and solving technical problems to become an indestructible symbol of San Francisco. This miraculous bridge surely leaves us in awe of its remarkable achievements.