Golden Gate Bridge Seismic Retrofit Project Wins Civil Engineering Award
With a 65 percent probability that an earthquake with a magnitude of at least 6.7 will strike the San Francisco region before the year 2030, the Golden Gate Bridge has long been considered vulnerable to significant earthquake damage. To protect this international icon of San Francisco and the United States, the Golden Gate Bridge Seismic Retrofit Phase II, South Approach Structures Project, retrofitted five structures of the bridge to withstand an 8.3 Richter scale-magnitude earthquake occurring 7 miles west of the bridge. Recognizing the project's success, the American Society of Civil Engineers on April 25 named it the ASCE 2007 Outstanding Civil Engineering Achievement (OCEA) award winner.
"The OCEA award not only recognizes exceptional planning, use of materials and innovations, but it also recognizes a project's contribution to the well-being of people and their communities," said ASCE President William F. Marcuson, Ph.D., P.E. "Not only did the Golden Gate Bridge Seismic Retrofit meet the challenge of complying with modern engineering standards and preserving the historic and architectural value of the bridge, but it did all of that while remaining open to traffic at all times during construction--which is why it is an exceptional example of everything the OCEA award embodies."
The retrofit techniques used--many of which had never before been employed--greatly decreased the magnitude of earthquake-induced forces in the structures (the south approach viaduct, the south anchorage housing, two south pylons, and the Fort Point arch), thus significantly reducing the extent and cost of the retrofit. Major modifications included completely replacing the viaduct supports and bottom lateral bracing; replacing the west wall and strengthening the east wall of the south anchorage housing; installing external and internal steel plating and an architectural concrete cover on the pylon walls and a high capacity tidown system at the pylon foundations; and installing uplift guides and impact force reducing devices at the bearings of the arch.
The project also minimized construction impacts on the surrounding physical environment, including construction operations and materials deliveries staged for continuous flow of vehicular, pedestrian and bicycle traffic; installations of platforms on the Arch, shielding Fort Pont from damage; a shuttle to the site for workers to minimize construction traffic impacts on local roads; and implementation of water, air and noise pollution prevention by The Environmental Monitor.
Currently the second longest suspension bridge in the United States, the Golden Gate Bridge is visited by millions each year and crossed by 40 million vehicles annually. Since opening to traffic in 1937, more than 1.7 billion have crossed the span. ASCE named the bridge a National Historic Civil Engineering Landmark in 1984, and it was designated as a Monument of the Millennium in 2000. Monday, May 28, will mark the 70th anniversary of the Golden Gate Bridge.