McNerney Reports on Tour of the San Francisco-Oakland Bay Bridge
I had the extraordinary opportunity this past week to tour the new Oakland Bay Bridge suspension section. The Contra Costa Transportation Authority invited me to see the structure and the engineering involved to gain a better appreciation of this and other bridge projects. The Bay Bridge is a critical part of the entire Bay Area and Northern California infrastructure, and is especially crucial for the livelihood of my district, connecting people with goods, services and jobs throughout the region.
The tour started with a meeting with two engineers, Mazen Wahbeh and Patrick Lowry, from Alta Vista, the quality assurance firm that oversaw the construction of the bridge. We discussed how the project was modeled, contracted, and constructed. I have a background in computer modeling of complex mechanical projects from my career in developing wind turbine technology, so we spent more time than expected talking about the details of the design process.
After our meeting, we proceeded to Pier 7, where Caltrans managed the bridge’s construction and continues to manage maintenance of the structure. We met up with Steve Whipple, the chief engineer on the project, and grabbed our hard hats, vests and gloves. The hats had to be equipped with headlights in case we got stuck climbing down from the tower or if the lights went off inside the bridge.
Pier 7 is on the Oakland side and since we had to enter the bridge from the eastbound traffic, we had to drive to San Francisco in order to come back to the new section of the bridge east of Treasure Island. Since it was about 2pm, the traffic was already heavy heading out of San Francisco, with cars inching along and merging onto the bridge in slow motion. After passing Treasure Island, we drove slightly past the sole tower to a set of barriers on the left side of the road. Steve expertly maneuvered our van to squeeze in between the two barriers to ensure that we were safe from the speeding traffic. We then got out of the van and climbed over the remaining barrier and headed toward the tower.
We rode in the tower’s glass-walled elevator and got a view north and watched the highway bridge fall away and see the Bay rise as the elevator ascended. It was a clear day with the marine layer moving in over the Golden Gate Bridge, and as the elevator rose, we could see the magnificent Bay Area.
The elevator moved slowly, but finally stopped at the very top of the tower, roughly 500 feet up. We got out of the elevator into a strong and steady wind. I was glad I had worn a windbreaker because it was pretty chilly. We were able to walk over to the edge to look down over the cables to the bridge below.
The bridge is unique because it is all steel and is the world’s largest self-anchoring suspension bridge. That means it acts like a teeter-totter, with the tower supporting the entire structure, i.e., the ends are suspended and do not rest on anything. The massive cables are actually a single cable that starts at the eastern section, goes up the tower and back down the western side, where it wraps around the western edge of the bridge and then travels back up to the top of the tower and strands back to the eastern edge, where it anchors with the eastern end. The western side is shorter than the eastern side, so counterweights are necessary. The south side of the bridge has a bike path, so the north side also has counter weights. The smaller cables that hang from the massive cable hold up the roadway. The roadway itself is an orthotropic structure - meaning it is not just a flat roadway, but has strength in the vertical and horizontal directions.
Up on the top of the tower, I had to hang on to keep from being blown over in the strong winds but got a magnificent view of the western span as the engineers reviewed the structure, its design and its construction. We hopped over the center of the tower to view the eastern section. Amazing! Finally, after going over the structural basics, we headed back to the elevator for the slow ride down the tower.
Once we were at the bottom, I thought the tour was over, but there was so much more to see. The bridge has a tunnel inside – remember, it is an orthotropic structure, so there is a whole cavern inside under the road, where a tremendous amount of construction took place and which must be inspected regularly to maintain the bridge.
The entrance was unlocked for us and we climbed down into what seemed like submarine doors to descend into the bowels of the bridge. There were no stairs, so ladders had to be used instead. Inside, I understood why our helmets required headlights. Lights on, we proceeded to walk a long plank, seeing the hundreds of miles of weldments that made up the welded ribs of the underbelly of the street. We proceeded up the sloped sides to get a close look at one of the cross beams.
The path went all the way to where the suspension portion of the bridge meets the causeway portion. At various points we had to traverse small submarine-like doors and ladders. When we reached the transition of the sections, we emerged from the tunnel to stand in open air on a mess section that allowed us to look down 190 feet to the Bay below. At this point, the engineers showed me one of the prized portions of the bridge. Overhead was what I called a mechanical fuse. It is about an 8-foot diameter section of material that connects the two sections of the bridge and was designed to give the bridge the flexibility to withstand any likely seismic event and allow the bridge to be used to evacuate the city if necessary. The old section of the bridge is now being removed because of the danger it would pose in the event of a major earthquake.
We had gone to the top of the tower, had gone inside the belly of the beast, and had seen this engineering and political marvel. The Bay Bridge is an impressive structure that is built to last for a long, long time, providing safe passage to literally millions of travelers every year and for years to come. With proper maintenance, the bridge should last at least 150 more years. My hat is off to the folks, engineering and political, who made it happen.
I want to thank Caltrans, Randy Iwasaki of Contra Costa Transportation Authority, and Mazen Wahbeh and Patrick Lowry from Alta Vista for making the tour possible.