The first major suspension bridge built in the U.S. in 30 years, the Al Zampa Memorial Bridge, opened in San Francisco Saturday. The bridge is unique for its design, which has towers made of hollow concrete instead of steel.
Constructing the towers out of heavily reinforced concrete saved tens of millions of dollars, according to the California Department of Transportation, and will be cheaper to maintain.
“Concrete can withstand forces now,” Bart Ney, a spokesman for the California DOT told the Mercury News. “And we don’t have to paint that tower, so we’ll save a lot of money over the years.”
The 410-foot towers support more than 88,000 tons of concrete and steel, plus 7,000 tons of people and vehicles. The walls of the towers are about a yard thick and contain elevators inside them. On each side of the two towers are giant suspension cables, which hold the bridge up with its 8,584 separate, spun wires.
Because the bridge is surrounded by faults and is in one of the windiest places in California, it had to be strong but also flexible. The bridge deck, which was built in Japan, brought over by ship and lifted into place, can move a couple of feet in any direction during an earthquake. According to the project engineers, OPAC Consulting Engineers of San Francisco, the bridge is designed to withstand a 7.1 earthquake. Its aerodynamic shape also deflects the wind.
The Zampa bridge is also the first bridge to have earthquake sensors built inside it, which will measure the response of the bridge to shaking. While more than 68 bridges across the country have had sensors installed since 1987, the Zampa bridge had 130 sensors installed during construction, from the bottoms of the pilings to the top of the towers. Officials hope that the sensors transmit information about how the bridge moves during tremors and strong winds, which will help to design strong structures in the future. The sensor readings are sent directly to a computer network, which help engineers determine within minutes of an earthquake whether it is safe for traffic to cross the bridge.
The memorial bridge was named after Al Zampa, an ironworker who helped construct the Golden Gate Bridge. During its construction in 1936 Zampa slipped and fell, but landed in a net. He escaped death, but broke four vertebrae. Other bridges he helped build include the Bay Bridge and two other bridges that span the Carquinez Strait. Zampa died in 2000 at the age of 95.