By Erin Sherbert
By Howard Cole
By Erin Sherbert
By Erin Sherbert
By Leif Haven
By Erin Sherbert
By Chris Roberts
By Kate Conger
The towers will be strengthened with concrete and metal, and the road decks bolstered with more steel. At the same time, giant shock absorbers and bearings will allow the bridge to diffuse the quake's destructive forces.
Each "friction pendulum bearing" used on the bridge is essentially an upside-down iron mushroom resting in a shallow dish topped by a "slider plate." The plate contains a groove that fits over the stem of the mushroom so the bridge can slide about three feet east and west (in the direction of traffic) on the support columns. A bearing will be placed between the roadway and each of four steel columns holding up the bridge at the San Francisco end near the Embarcadero.
Ninety-six 20-foot shock absorbers, called "dampers" -- some of the world's largest -- will also be added where the roadway meets the towers in the middle of the bay to prevent the road deck from slamming into the towers during an earthquake.
Perhaps the most noticeable change will be the removal of the archaic and unstable steel crosshatching or "lacing" that can be seen all over the bridge, particularly on the diagonal steel beams connecting the upper and lower decks. Ironworkers will remove the rivets that hold the steel strips and replace them with "perforated plates," or steel sheets with ovals punched into them.
The retrofit has been divided into three projects. The first, Project 15, began in April 1998 with the strengthening of the foundations in the water. It took a little less than two years to complete.
The second and third projects began in 1999 and are going on simultaneously. Project 16 focuses primarily on adding concrete and steel to the anchors and support columns near the Embarcadero. Project 16, which should be completed by 2002, is also responsible for jacking up the bridge and installing the four bearings in the next few weeks.
Meanwhile, Project 18 involves all the work on the bridge itself: removing rivets and lacing and installing the perforated plates; strengthening the road decks with more steel; and adding the dampers. It should be completed by 2003.
For all its complexity, the retrofitting is a fairly standard construction job, Caltrans officials say. It is the traffic that makes it hard, and because of it, the five-year retrofit will take about two years longer than it took to build the bridge 60 years ago.
In a labyrinth of high-walled cubicles in his Sacramento office, Mark Reno, a Caltrans senior engineer, designs and retrofits bridges, a can of Diet Dr Pepper near at hand. Six years ago, the immense task of masterminding the Bay Bridge retrofit fell to Reno, a 13-year Caltrans veteran who is considered a "design guru" by his colleagues. For two years, he worked feverishly on the retrofit, logging 60-hour weeks with his staff.
Retrofitting can be more difficult than building a new bridge, Reno says, because it requires molding a pre-existing steel bridge into something it was not necessarily designed to be.
"It's frustrating sometimes," he explains. "Say you decide to put a beam here, and then you go down there [to the bridge] and you see there's no way it will fit, or there's utilities hanging off the thing. These are the things we're running up against."
Reno began by inspecting every spot on the bridge to understand its layout. Yet even before he could begin designing, he ran into a critical problem. Reno needed the original shop drawings of each individual piece of steel to develop the retrofit plans, but when he turned to the old microfiche on which the drawings had been stored, he found them so blurry that they were completely unreadable. His only alternative was to use the original shop plans themselves -- except no one knew where they were.
After asking around the office and making a few phone calls, Reno found someone from the Oakland of- fice who mentioned that Caltrans kept documents in an old storage space in a section of the bridge that Reno declines to reveal. A fire several years ago had damaged some of the boxes there, and no one knew what condition the Bay Bridge drawings might be in -- if they were there at all.
A few days later, Reno was in a car heading toward San Francisco with another engineer, with a handwritten map of the storage space.
"Inside we found this huge box [of Bay Bridge plans], and we didn't have a screwdriver so we couldn't open it," Reno says. "We had a state car, so we loaded this box into the trunk and had to drive back to Sacramento with the trunk open. [The plans were in] ink on linen sheets, stored in a plywood box with brass screws. It probably hadn't been opened since someone put it there [in the '30s]. It was like Raiders of the Lost Ark."
Reno's detective work led him to other obscure outposts and more hidden documents. "A lot we stumbled upon, when we were looking for [the plans]," he says. "In the basement of the toll plaza, we were leafing through boxes and we found the actual typed diary the resident engineer kept every day of the wind and things that happened that day. It was fascinating. We found diaries of construction. Some of the documents said things like wages were $1 a day, or there were restrictions on ethnicity, like no Chinese workers.