EAST SPAN, BAY BRIDGE MAP
At 5:04 p.m. on Tuesday, October 17, 1989, when Bay Area commuter traffic was at its heaviest and more than 62,000 fans filled Candlestick Park for the third World Series game between the Oakland Athletics and the San Francisco Giants, an earthquake with a 6.9 magnitude struck. Twenty seconds later, the Loma Prieta Earthquake was over. Sixty-three people had died and a portion of the eastern section of the San Francisco-Oakland Bay Bridge had collapsed.
The Bay Bridge, as it was known locally, was a preeminent engineering feat of the last century, a crossing that had been wanted since the California Gold Rush era. The 8.4-mile (13.5-kilometer)-long bridge was realized in 1936, under the direction of the state’s highway engineer, Charles H. Purcell. Purcell conceived of two discrete crossings linked by a tunnel bored through the island of Yerba
Buena. In its entirety, the bridge consisted of the west bay crossingtwo end-to-end suspension bridges with 2,310-foot (704-meter) main spans and 1,160-foot (354-meter) side spansa half-mile tunnel through Yerba Buena, a long viaduct to the Oakland shore, and the cantilever bridge over the east bay that collapsed in 1989. When the earthquake hit, bolts holding a section of the upper deck of the truss section were sheared off, and the upper deck fell onto the lower deck.
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Shine it forward.
Used daily by tens of thousands, the deck was repaired, but it was a temporary measure. The costs of a seismic retrofit were so highmore than $1 billion that the California Department of Transportation (Caltrans), the owner, determined a new crossing would be more cost-effective. To appease Bay Area residents who were agitated about changes to the skyline, Caltrans created online bridge simulations that allowed viewers to “fly through” the designs under consideration. A joint venture of T.Y. Lin and Moffatt & Nichol, in collaboration with Caltrans and city and state transportation commissions, delivered the seismically resilient bridge in 2013.
When the East Span opened, it made engineering history: it is the longest singletower self-anchored suspension span (SAS) in the world at 2,047 feet (624 meters) and, with a width of 259 feet (79 meters), also the widest bridge.
Its singular innovations respond to the site’s difficult geology and seismic vulnerability. Because these conditions made it unfeasible to anchor a suspension cable system in the ground at either end of the structure, the main cable is anchored in the superstructure itself, an industry first. The suspended span is carried by a single, 4,550-foot (1,387-meter)-long cable, the longest looped cable ever used. Shock-absorbing shear link beams allow the four legs of the 525-foot (160-meter)-tall SAS tower to move independently during an earthquake, another first. Beyond its 150-year life, Caltrans’s criteria specified that the bridge must be able to stand, remaining open to emergency vehicles, even after the most powerful earthquakein the next 1,500 yearshits. To date, California’s newest technological feat has won twenty-one national and international awards.
The last segment of the East Span’s 4.5-mile (7.2-kilometer)-long, 15.5-foot (4.7-meter)-wide bicycle/pedestrian path opened in 2016.
The East Span is a four-part invention: the 2,047-foot (624-meter)-long SAS; 6,234-foot (1,900-meter)-long skyway that carries five lanes of traffic in each direction; a 4,229-foot (1,289-meter)-long span that links the skyway to Interstate 80, and the 1,541-foot (470-meter)-long structure that connects the SAS to the Yerba Buena Island Tunnel.
The West Span flickered to life in 2013, illuminated by 25,000 LED lights. The Bay Lights, a monumental public art installation by artist Leo Villareal, shone every night for two years, until 2015. In 2016 the piece was permanently reinstated, thanks to funding from Illuminate, a nonprofit organization.
Lighting amps up drama, even on already theatrical bridges like the Dragon Bridge (2013) in Da Nang, Vietnam, which incorporates a dragon that can spit water or breathe fire. It demanded an equally dramatic presence on ordinary nights, but the number of fixtures needed to illuminate the 2,185-foot (666-meter)-long bridge could have been a huge energy drain. Philips Color Kinetics lit the dragon’s head, body, and tail with high-output, high-performance luminaires.