SAN FRANCISCO-OAKLAND NEW HOME TO THE LONGEST SELF-ANCHORED BY STEPHANIE AURORA LEWIS
“Where is the safest place to be in San Francisco when the soon-coming Big One strikes,” asks Ira Flatow, the host of NPR’s Science Fr iday, joking with his audience. Marwan Nadar, PhD, the Lead Design Engineer of the San Francisco-Oakland Bay Bridge answers Flatow’s question, “the safest place in the Bay area may indeed be sitting in your car on the new eastern span on the Self-Anchored Suspension (SAS) Bridge.” Marwan Nadar represents T.Y. Lin International who joined with Moff att Nichol Engineers as a joint venture company to design the new SAS Bay Bridge for Caltrans, the California Department of Transportation. Of all the materials used in Nadar’s avant-garde seismic bridge design, wire rope is the key element.
QUAKE OF ‘89 On October 17th, 1989, the San Andreas Fault shifted to produce the devastating 7.1 magnitude Loma Prieta earthquake which shook the Bay area long and great enough to cause billions of dollars of damage and a renewed fear for seismic movements. Many Americans remember this earthquake because it delayed the World Series Game T ree that took place that year in San Francisco between the Oakland Athletics and the San Francisco Giants. T e original Bay Bridge was designed by the chief engineer Charles Henry Purcell in 1936. Later in 1955, the American Society of Civil Engineers named the Bay Bridge as one of the seven modern civil engineering wonders of the United States. When the Quake of ’89
22 MARCH-APRIL 2013 WIRE ROPE EXCHANGE
shook, the eastern part of the bridge shifted seven inches, causing the bolts of one section to shear off , sending a 250-ton section of the bridge’s roadbed crashing down. T e crash caused one car to its fatal plunge and bridge closure for 30 days.
THE FUTURE BRIDGE Caltrans is the project’s client who set serious goals for the new Bay Bridge to make sure that history would not repeat itself as it did on that tragic day in 1989. First of all, the existing bridge of 1936 was a structural steel truss system that would have been too diffi cult to retrofi t and repair for updated seismic prevention design. Secondly, the bridge needed to be able to survive for 150 years. T irdly, the bridge was to withstand
BAY BRIDGE
Copyright (2012) California Department of Transportation, Photographer: Bill Hall
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