Sixty years after it was built and nearly a decade after it was seriously damaged in a major earthquake, the San Francisco-Oakland Bay Bridge is about to get a major face-lift. The entire east span, a two-mile stretch from Yerba Buena Island to Oakland, will be replaced with a structurally superior single-tower suspension bridge designed to withstand an 8.5 magnitude quake on the San Andreas Fault.
But unlike their predecessors six decades ago, engineers designing the bridge's new incarnation have the benefit of a wealth of computing technologies to facilitate the $1.4 billion project. All facets, from conceptual planning through detailed design and construction, rely on information technology applications covering such areas as computer-aided design (CAD), three-dimensional structural analysis, seismic modeling, animation and digital imaging.
The California Department of Transportation (Caltrans), with the Bay Area Metropolitan Transportation Commission (MTC) and Bay Bridge Design Task Force, recently finalized the conceptual design of the new bridge structure. Caltrans and its consortium of design consultants, led by T.Y. Lin International, are readying hardware and software to take the project from its current partial design through scheduled completion in 2003.
"We're aggressively using technology to help us manage this very large-scale project," said Denis Mulligan, Caltrans' toll bridge program chief. "It's how we're achieving our goal, which is to make the Bay Bridge seismically sound."
Technology as a Marketing Tool
Information technology made its first contribution to the project early in the planning phase, as a tool to help transportation officials sell the proposed design to citizens' groups and others concerned about the project's visual impact. Using a computer-generated 3-D model of the Bay Area, Caltrans planners were able to simulate views of the bridge from any point around the bay.
Animation portrayed proposed structures as seen by motorists crossing from either end. Graphical representations of four proposed designs were placed on the MTC Web site , where visitors could vote on their favorite design.
From Concept to Construction
Long before construction crews begin laying the foundation piers for the new bridge sometime in 2000, designers will have "built" and analyzed every inch of the span in the form of computer models. Advances in desktop PC computing power now enable engineers to readily conduct complex structural analyses of all critical bridge components early in the design phase.
Using proprietary software developed in the last five years by ADINA Research and Development Inc., of Watertown, Mass., structural engineers create an onscreen stick model of the new bridge span. The software subjects the bridge model to timed pulses programmed to simulate a quake of a desired magnitude. The results allow engineers to see graphically where bridge components might break apart so that structural connections can be strengthened.
"The design of bridges has changed dramatically," said Mike Whiteside, Caltrans' assistant contract manager for the Bay Bridge replacement project. "The Cypress Freeway failures caused by the 1989 Loma Prieta earthquake pushed Caltrans to the forefront of new computer design techniques that are now used throughout the country."
Similar computational analyses were used successfully by T.Y. Lin in designing seismic retrofits for the Bay Bridge's more famous neighbor, the Golden Gate Bridge, completed in 1937. Structural members of the lower portions of the main tower legs were modeled and rocked with simulated earthquakes to see how the tower legs would lift off their concrete base during seismic events of magnitudes up to 50 percent stronger than those the bridge was originally designed to withstand.
But unlike bridge designs of the 1930s, which consisted of large numbers of smaller steel components riveted together, newer bridge designs use larger steel and concrete members that can be readily modeled on most high-performance PCs. The models created for the Golden Gate Bridge analysis consisted of some 67,000 parts, requiring the processing power
of a Cray C90 computer.
Computing power is also playing a key role below the water line, in the design of the foundations for the new bridge's 530-foot support tower. A barge serving as home to a floating soils laboratory allows geotechnical engineers to gather realtime data from borings of mud formations more than 200 feet below the bottom of the bay. The results of critical soil strength tests are transmitted by wireless link to onshore offices, where they are used by engineers designing the foundations. Sonic methods are also used to create a 3-D map of the topography on the bay floor.
"This use of technology at the boring site is helping tremendously to speed up the geotechnical work and foundation design," said Steve Hulsebus, Caltrans' contract manager for civil and environmental engineering. "We can position the barge over several proposed foundation locations and compare the data very quickly. It's facilitating our aggressive schedule."
Traffic models will also be prepared, letting designers compare the bridge's vehicle capacity to known demand data. The new bridge's side-by-side roadway design will carry an estimated 280,000 motorists each day.
Linking the Design Team
With more than a dozen engineering and planning firms working on the project, Caltrans officials have established strict policies for managing the transfer of data between design groups. And while no dedicated WAN has been set-up for the project, a Web site -- accessible to members of the design team only -- has been established to serve as a vehicle for exchanging hundreds of CAD drawing files, schedules, meeting agendas, minutes, design calculations and other project data that will be generated during the planning and design phases. The agency also uses teleconferencing to hold weekly coordination meetings between its headquarters in Sacramento, Calif., and design engineers in the San Francisco Bay Area, 85 miles away.
"The coordination challenges alone are daunting," Mulligan said. "But our consultant teams are required by contract to use common platforms for exchanging information. We regulate that very carefully."
Those platforms include Micro- Station design and drafting software by Bentley Systems Inc., Adena structural modeling and analysis software, an Oracle-based cost-estimating database and Primavera project-scheduling software.
In late August, Caltrans agreed to purchase $2 million in Bentley MicroStation software, bringing its total of CAD workstations up to 3,000. Under the deal, Caltrans will receive software licenses for new and recently upgraded PCs, training and product support from Applied GeoDynamics, an independent value-added reseller of Bentley products.
Mulligan admits the myriad of hardware and software programs used in today's bridge design would no doubt raise an eyebrow or two among the slide-rule-toting bridge designers of yesteryear, but he sees the reliance on technology as a natural progression because of the amount of information needed for design and construction.
"We know more about earthquakes and their effects than they did 60 years ago," Mulligan said. "The technology allows us to model ground motion during a seismic event and see the impact on intricate bridge connections. That's a tremendous advantage."
Those advantages will be exploited during construction as well. Caltrans bridge inspectors will use portable computers and digital cameras to document each phase of construction, including demolition of the old bridge once the new structure is opened to traffic. Digital images captured during daily construction inspections will be readily distributed electronically throughout the organization, giving engineers and program managers the opportunity to see their designs evolve into concrete and steel.
The digital images are also valuable tools in resolving claims with contractors, Mulligan said, because inspectors can use date-stamped digital images to identify exactly when problems occurred.
Sight of the Times
When the mammoth span opens to the public early next century, its distinctive single tower will no doubt establish a new visual landmark for the San Francisco Bay Area. But to Mulligan and his team of engineers, programmers and contractors, the modern structure will also serve as a monument to the vital role tools of the Information Age played in making it safe for motorists.
Tom Byerly is a Sacramento, Calif.-based writer.
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