Aug 14, 2019 10:40 AM EDT
San Francisco is well-known for its bridges and its skyline, and the new Bay Bridge in San Francisco is one of the newest additions that has significant historic importance.
The San Francisco Bay Area is no stranger to earthquakes, and the next one is inevitable. But when the next earthquake does hit, the 8.4-mile long San Francisco-Oakland Bridge that unites San Francisco and Oakland will be ready for it. The bridge is now referred to as the 'new Bay Bridge' after recent construction on it. Although there were other parts of the bridge that were improved, the main portion of the construction was on the 1.2-mile eastern span that stretches from Oakland to Yerba Buena Island. The eastern span replacement for the new Bay Bridge started construction on January 29, 2002 and was completed on September 2, 2013. According to the website of the California Department of Transportation dedicated to the new Bay Bridge, "The new East Span has been designed to withstand rare seismic events. Specifically, the span has a 1,500-year return period. This is defined as the largest rock motions expected to occur at the bridge site once every 1,500 years."
The project totaled $6.4 billion and was built to withstand seismic activity. Features of the span include unique battered piles made of steel pipes 8 feet in diameter that are angled through the ground into other structures and then filled with concrete. Mike Whiteside, a Caltrans engineer who worked on the seismic system explained that after significant testing done in laboratories from Reno to San Diego, there were features of the new bridge that are included particular to this project. The battered piles are an example of a seismic precaution that was used particularly for the Bay Bridge.
Another way in which the new Bay Bridge was built to withstand an earthquake was via the foundation of the structure. The new East Span includes a 1.2-mile Skyway that consists of a 525-foot tower. The shock-absorbing beams that support the four legs of the tower will be able to move during the event of an earthquake and minimize impact and damage. As needed, the damaged parts can then be replaced.
Similarly, Caltrans fit hinge pipe beams at points of the span that will experience the greatest stress during an earthquake. Because of the hinge, they can slide back and forth and pull the energy to the center of the beam.
The original Bay Bridge, built by American Bridge Company for Columbia Steel Company, was once the longest bridge in the world when it opened in 1936. It had two decks to accommodate for significant traffic flow, one for cars and one for trucks and trains below. At both high risk, due to strong winds and the choppy bay, and high cost for the construction of the bridge it turned out to be a successful build. However, when the 1989 earthquake hit that reached 7.0 on the Richter scale the entire San Francisco Bay Area was hit hard. As a result, a 250-ton section of the Bay Bridge's upper deck of the East Span collapsed.
It was vital for the infrastructure to be made safe for the new Bay Bridge, and taking the time to construct it properly was crucial in order to withstand the next earthquake.
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