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
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