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Features May 2007: Volume 4, Number 2

Building Bridges
By Daniel Kane

Kevin Smith, Marshall '93, is the structural engineer responsible for draping the 137-mile-long, pre-fabricated parallel wire strands over bridge towers of the new East Span of the San Francisco-Oakland Bay Bridge.

“I’m not aware of any suspension bridge that even has a U-shaped loop like this,” says Smith. “It’s all innovation to do this work. So much of this has never been done before.”

Kevin Smith, B.S. ’93, likes to see 35-ton spools of steel strand slowly unravel, high above San Francisco Bay. “As long as the strand is still moving, it’s a good indication that things are going well,” says Smith.

For Smith, a structural engineer, “things” refers to draping 137 pre-fabricated parallel wire strands, each almost one mile long, over the tower of the suspension bridge that is part of the new East Span of the San Francisco-Oakland Bay Bridge. The strands are hauled up and over the 525-foot bridge tower, then shaped and tensioned with millimeter precision. Together the strands will function as a U-shaped sling—the main suspension cable that will hold up the roadway of the new bridge.

The cable hauling system is just one of Smith’s many responsibilities as technical director for American Bridge/Fluor Enterprises, Inc., A Joint Venture, the company that is building the bridge, officially named the Self-Anchored Suspension Span (SAS). The new East Span, which includes the SAS, is scheduled to open Labor Day Weekend 2013, and will replace the existing span, which suffered a collapsed upper deck during the 1989 Loma Prieta earthquake.

Smith has been at work on the SAS since construction began in 2006. (Another company did the foundation work, which started in 2002 after lengthy debate over the design of the replacement span.) The East Span is designed to withstand the largest earthquake-triggered ground motions expected at the bridge site within the next 1,500 years. The comprehensive seismic design includes replaceable “shock absorbers,” some of which were tested in the Department of Structural Engineering at UC San Diego. The four legs of the bridge tower, for example, are connected by “shear link beams” designed to absorb most of the damage-causing energy during an earthquake. This will spare the bridge of damage to components that are not so easily replaced.

WIRED: Smith, a structural engineer, oversees the hauling of 137 pre-fabricated, parallel wire strands, each almost one mile long, up and over the 525-foot bridge tower of the suspension bridge.

Temporary Works

For Smith and the teams of engineers he oversees, the final design of the suspension bridge is the starting point. Smith determines what tools, systems and infrastructure—the “temporary works”—need to be designed and built in order to construct the bridge.

The design, for example, called for the suspension span to start at Yerba Buena Island and extend east 2,047 feet across San Francisco Bay. Here, above the water, the suspension span connects with the 1.2-mile skyway that reaches Oakland.

Having the suspension span and skyway connect above water, not land, was one of the design features that necessitated the U-shaped suspension cable—which in turn led Smith to envision, design and execute his innovative cable hauling system in order to actually build the bridge.

“I’m not aware of any suspension bridge that even has a U-shaped loop like this,” says Smith. “It’s all innovation to do this work. So much of this has never been done before.”

The “self-anchored” in the suspension span’s name highlights another significant aspect of the bridge design: the U-shaped cable anchors into the bridge deck itself. This differs from typical suspension bridges, such as the Golden Gate, where two cables (not one U-shaped cable) lock into large concrete anchorages on land at both ends of the bridge.

“One advantage of the self-anchored bridge is that the cable comes last not first, so we had time to develop some fairly elaborate techniques [for installing the cables],” says Smith. “In traditional suspension bridges, you build the cables first, and they anchor into concrete anchorages, and you hang the box girder (the sections of the bridge that vehicles will drive on) from the cables.” In contrast, for the Bay Bridge project, Smith had to build a temporary platform—the truss—to hold the box girder sections until the main cable was installed, anchored and ready to hold up the bridge’s roadway.

Well before the crews connect the cable to the roadway and lift it up off the temporary truss, Smith will have already mapped out all the technical details to ensure it goes safely and smoothly. This is another aspect of Smith’s job—preparing and overseeing detailed erection plans for performing the major lifts and other high-stakes moves in the construction process.

For example, Smith planned the lifts performed by the Left Coast Lifter, the project’s crane mounted on a barge. The crane moved 28 sections of bridge deck from boat to barge, and then from the barge to the temporary truss 150 feet above the water.

The bridge deck sections are light for their size—and, like soda cans, they are strong in some ways but not others. This meant that each section could only be lifted at precise locations. To do this safely, Smith designed an adjustable “lifting frame” that attached to rods at specific locations on each bridge deck section.

“Kevin is the epitome of an engineer,” says Brian Maroney, deputy program manager at the California Department of Transportation (Caltrans) who works closely with Smith. “He is smart, hard working and patient. Kevin allows the bridge to be better, the project to be better.”

Smith has worked on projects across the world, including the major expansion of an iconic suspension bridge in Lisbon, Portugal—the Tagus River Bridge; the retrofit of the Lions Gate suspension bridge in Vancouver, Canada; and the construction of the Florida Avenue Bridge in New Orleans.
The Florida Avenue Bridge spans an industrial canal connected to the Mississippi River in New Orleans’ 9th Ward. Smith completed work on it just a month before Hurricane Katrina struck in 2005. There was flood damage but the bridge survived the hurricane.

Making bridges better is something Smith has been doing since his days in the structural engineering department at the Jacobs School of Engineering. “We had a structures lab where we made a bridge intended to support a certain amount of weight and actually fail at a predetermined weight. And I didn’t do very well in the lab. My bridge was very, very strong,” says Smith with a smile. “I’ve carried that into my work now because I really like it that way.”

Daniel Kane is director of media relations and public affairs for the Jacobs School of Engineering at UC San Diego.