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December 1998: The Military Engineer
The most extensive bridge seismic retrofit program ever undertaken in the U.S., and one of the largest worldwide, will make California's bridges safer and improve the state's infrastructure. The $4.5 billion program launched by the California Department of Transportation (Caltrans) encompasses inspecting and testing the structural materials on more than 2,200 bridges in California, including seven major toll bridges. The Office of Materials Engineering Testing Services (METS), part of Caltrans, and LAWCRANDALL, a division of Law Engineering and Environmental Services, Inc. (LAW) have been working closely on this program. This project includes the testing of structural steel materials and their components such as welding, bolting and existing rivets to ensure that the appropriate level of quality is maintained during construction.
The toll bridge retrofit program encompasses the Benicia-Martinez Bridge; Carquinez Bridge; Richmond-San Rafael Bridge; San Francisco-Oakland Bay Bridge (East Span Retrofit & West Approach Replacement); San Mateo-Hayward Bridge; San Diego-Coronado Bay Bridge; and Vincent Thomas Bridge. The last two bridges are in Southern California, the remainder in the San Francisco Bay Area. The current effort is part of the Caltrans Seismic Retrofit Program that was initially launched in 1989 shortly after the Loma Prieta Earthquake. METS and LAW are working closely together on a wide range of quality assurance inspection issues, including welding inspection-both visual and nondestructive testing (NDT). The nondestructive testing portion consists of radiographic testing, ultrasonic testing, and magnetic particle testing. The team members performing the inspection and testing are qualified and certified by the American Welding Society (AWS) as Certified Welding Inspectors (CWI), and the team members performing NDT are certified as Level II and/or ASNT Level III NDT technicians.
The retrofit program involves using current welding standards for design and inspection, in conjunction with the Caltrans Standards, Specifications and Special Provisions. A number of the engineers currently working on this project are also involved in the development and writing of the AWS Structural Codes and Standards, including the AWS D1 Subcommittee for seismic engineering interests. While volumes could be written about retrofitting the toll bridges statewide, we'll provide a short synopsis on key aspects of some of the toll bridge projects.
Benicia-Martinez Bridge - Built in 1962, this bridge carries State Route 680 traffic over the Carquinez Strait between the cities of Benicia in Solano County and Martinez in Contra Costa County. Currently, over 90,000 vehicles cross the bridge each day. The toll bridge is a 6,215-foot long, high-level, deck type structure with a welded truss bridge and welded girder approach spans. The 33-foot deep truss section of the bridge spans a waterway width of about 5,000 feet, consisting of seven 528-foot spans, two 429-foot spans and one 330-foot span.
The challenges here involve the welding of high strength quench and tempered materials to accomplish the designed retrofit. The challenge is to develop welding procedures that will allow the material to remain sufficiently strong, ductile and tough. Construction costs are estimated at $105 million and the project is slated for completion in June 2000.
Carquinez Bridge - The two Carquinez bridges carry approximately 104,000 vehicles per day along Interstate 80 across the Carquinez Strait between Contra Costa and Solano Counties. The main span is a 3,350 ft. long steel through cantilever truss superstructure, comprised of a steel-braced substructure, concrete caissons, steel pile footings, reinforced concrete and a 174,200 square-foot deck area. This project will present both engineering and cultural challenges. Key elements include replacing or strengthening steel truss members in the bridge superstructure and towers and reinforcing pile foundations at the south end of the bridge. The steel retrofit pieces are being fabricated at a plant near Shanghai, China. The METS and LAW team will work closely with the Chinese fabricator to ensure that the components (girders, tub girders, etc.) strictly adhere to AWS and Caltrans codes and standards. In addition to language and cultural differences to overcome, China's system of measurements is metric while the structure itself is imperial. Drawings will be used concurrently in both Chinese and English. Project costs are $86 million, completion date is set for December 2000.
San Francisco-Oakland Bay Bridge: The Bay Bridge is a vital east-west Bay Area transportation link and carries about 280,000 vehicles per day. The original bridge span (the old East Bay Bridge) is about 60 years old, containing a double-deck, steel cantilever truss bridge. This bridge sustained significant damage during the '89 Loma Prieta earthquake. The new East Bay Bridge will replace this eastern span and cost about $1 billion. It will open to traffic in February 2003. The west approach involves retrofitting the main line Interstate 80 and on-and off-ramps in San Francisco, including modifying the ramps at the Transbay Transit terminal. Some of the retrofit work on the piers in the Bay may require work to be performed from barges anchored to the piers.
The METS and LAW team will in effect, serve as the eyes and ears for the Caltrans Resident Engineer to provide important information and consultation regarding the contractors adherence to the quality standards. The METS and LAW team will also serve as a vital technical resource to the Resident Engineer concerning complicated materials and joining questions. This information will be utilized in determining if the contractor has met the design criteria and adhered to the contract documents. From the beginning of design through construction, the entire Caltrans effort is to ensure and provide for the safety of the public while providing as little inconvenience as possible. All of these efforts must come together to provide a technically sound, economical project that will meet the published schedule. San Mateo-Hayward Bridge: The first major orthotropic steel span bridge in the U.S. opened in 1967 and now carries 77,000 vehicles per day. The main span steel structure is 1.85 miles; the concrete trestle structure is 5.0 miles. Key features of the $150 million retrofit project, now underway, include adding steel casings for columns, strengthening bent caps and seat extensions. A series of large lateral load pipe piles are being driven into the Bay with a pile-driving hammer specifically designed for this project. These piles are the largest lateral load piles ever driven into the Bay - 150' long, 12' in diameter, 2" thick, made up of 10' sections welded together. Much of the project will be constructed under live load to limit lane closures. Coronado Bay Bridge: Connecting San Diego and Coronado Island, the 66' wide toll bridge consists of 17 approach spans on the west side of three main channel spans, and 11 approach spans on the east side. The approach superstructure consists of built-up steel plate girders with a lightweight concrete deck.
The primary challenge of this $95 million retrofit project involves the difficulty in accessing, removing and installing materials in a closed superstructure. Peening procedures were used to help in distortion control and to relieve residual stresses due to difficult member geometry and thick and heavy welds. Other major items of work are replacing existing bearings with isolation bearings; reinforced concrete casement of the columns; strengthening the marine pier pile caps; and jacking of the marine pier piles.
Obviously, these are just brief snapshots. The experience gained from the California bridge seismic retrofit project will ultimately prove invaluable to any future construction within seismically active areas. These bridge retrofits are a major step forward in providing for public safety while maintaining major routes for city, state and interstate commerce.
Return to: 1998 Feature Stories