Seismic Bridges

April 2, 2018
The bridge protection program

About the author: Schurr is a New York-based freelance writer and WTS-LA member who covers transportation issues for leading national and international publications.


For Caltrans and Randell Iwasaki, there’s no such thing as a bridge too far. Bridges epitomize strength. These tall, majestic structures provide vital transportation links, connecting landmasses that were once considered irrevocably distant. Usually taken for granted, bridges have become an almost invisible necessity—an extension of the road—that is only noticed by the odd tourist or during a particularly lurid sunset. However, there are certain other occasions that bring bridges into sharp relief. Though bridges are safer than a host of other places, crossing one during an earthquake makes people really notice a bridge, its construction and its stability. And nowhere is this more vividly demonstrated than in California.

California is earthquake country, so its bridges have a special significance. With more than 12,000 of them in the California state highway system—and an additional 11,500 city and county bridges—bridge performance and safety are very important issues. But not all bridges are equal. And with their exceptional size, length, traffic volume and engineering sophistication, toll bridges warrant particular attention. Their integrity is paramount. To protect these vital structures, the California Department of Transportation (Caltrans) created the Toll Bridge Seismic Retrofit Program (TBSRP). Of necessity, this is a very large program; the current budget authorized by AB 1171 is $5.085 billion.

A solid seven

“California has always focused on the safety of its bridges and other infrastructure with respect to seismic activity. That just goes with the lay of our very seismically active land,” explained Caltrans Chief Deputy Director Randell Iwasaki. Speaking recently at a reception hosted by the Los Angeles chapter of WTS (formerly Women’s Transportation Seminar), Iwasaki briefed WTS-LA members about the status of the TBSRP. As he pointed out, “The seismic retrofit program was inspired by the 1989 Loma Prieta earthquake, and the need was re-emphasized by the 1994 Northridge earthquake. Damage sustained during those earthquakes, and the knowledge gained as a result, led to a greater level of sophistication in terms of seismic mitigation. After the Loma Prieta earthquake, Caltrans inspected all nine of California’s toll bridges; we discovered that seven of them needed seismic retrofitting.”

The seven bridges that Iwasaki refers to are the Benicia Martinez, Carquinez, San Francisco-Oakland Bay Bridge, Richmond-San Rafael, the San Mateo-Hayward Bridges in the San Francisco Bay Area and the San Diego-Coronado and Vincent Thomas Bridges in southern California. According to the terms of AB 1171, Caltrans was authorized to allocate $4.637 billion to retrofit California’s toll bridges, with a program contingency of $448 million to come from state highway account funds. To date, five of the seven bridges have been completely retrofitted; retrofit work is continuing on the Richmond-San Rafael and San Francisco-Oakland Bay bridges. According to Iwasaki, the work on the first five bridges established some important precedents.

“Our toll bridges are the largest and most complicated bridges in the state. Consequently, these are by far the most complex seismic retrofit schemes ever undertaken. In fact, I am unaware of bridges this complex being seismically retrofitted anywhere else in the world. Our program and project team had to deal with numerous challenges, including variable soils and foundations, seismic forces nearly 10 times the original design forces, aged structures, conflicts with utilities, airspace concerns, handling of hazardous waste and the need to protect sensitive resources. And a considerable amount of the retrofitting was done in live traffic environments. So this was no trivial undertaking.

“Many people focus on the work that remains to be done. But I think it is noteworthy that, compared to AB 1171 estimates, we saved more than $48 million while completing the first five bridges. And much of that success is a direct result of the excellent working partnerships that we’ve had with the resource agencies, regional partners and the private sector. Through the considerable efforts of our in-house people, and the support and expertise that the private sector has provided, we’ve been able to make California’s toll bridges safer for the traveling public—and at a very reasonable cost. I would also like to recognize the traveling public for the considerable patience they have shown while we were retrofitting these bridges.”

With a total of $2.3 billion spent so far, $2.241 billion remains for the Richmond-San Rafael Bridge and the San Francisco-Oakland Bay Bridge. Costing approximately $914 million, work on the Richmond-San Rafael Bridge should be completed by August 2005. Even though this was one of the most complex marine foundation retrofit projects ever undertaken on a bridge structure, the Richmond-San Rafael Bridge nonetheless underwent its seismic retrofit under live traffic conditions. Twenty 5-ft sections of the trestle were removed and replaced during the night so that morning commuters could use the bridge without interruption and, in most cases, without even realizing that they were driving on new sections of bridge. With the challenges mostly met on the Richmond-San Rafael Bridge, only the San Francisco-Oakland Bay Bridge work remains.

A Bay change-up

Damaged during the 1989 Loma Prieta earthquake, the San Francisco-Oakland Bay Bridge presented its own unique challenge. Divided into two spans—east and west—the bridge requires a separate angle of attack for each distinct structure. Consisting of twin end-to-end suspension bridges and a three-span continuous truss structure, the west span was a particular challenge. The retrofit effort had to focus on four major structural elements: the foundations in San Francisco Bay, the anchorages, the towers and the superstructure. Beyond installing isolators and dampers to transfer seismic forces and restrict movement, the project entails a retrofit of the west span itself and replacement of the west approach. At present the west span retrofit is almost 100% complete, and the west approach replacement project is about 40% complete. The west approach project entails removing and replacing the viaduct. This is going to be accomplished with traffic on the structure; it is one of the most complex construction staging efforts Caltrans has ever undertaken.

Connecting Yerba Buena Island to Oakland, the 15,434-ft east span needed full replacement (rather than retrofitting). To be built on an alignment north of the existing bridge, a skyway bridge will be constructed in four major sections: (1) the Yerba Buena Island transition, (2) a connector span (the type is as yet undecided), (3) a precast segmental concrete skyway and (4) the Oakland approach and touchdown. Following construction and the transfer of traffic onto the new east span, a demolition contract will be let to remove the existing bridge. But although most of the engineering challenges have been met, the funding issues have continued to receive quite a bit of attention.

Initially $80 million was allocated for the span’s replacement. However, a number of factors have changed the cost considerably over time, including the fact that, by law, the Bay Area’s Metropolitan Transportation Commission has the legislative authority to select the type of connector span to be built. The cost estimate in AB 1171 for a self-anchored suspension bridge was $2.6 billion. Today, because of rising steel prices, higher insurance and bonding costs (triggered by terrorism concerns), the engineering complexity of the new span and several other critical factors, that estimate now hovers at $5.13 billion. This estimate assumed an award of the contract in September 2004. With the project still due to be completed in 2011, Iwasaki and Caltrans have worked tirelessly to keep costs down in every way they can, including the way that contracts have been structured. “Rather than issue one large contract, we split the project into 16 separate contracts. And we did that for two very good reasons. First, when you utilize a large-contract approach, you greatly limit your candidate pool for bidders. We wanted to maximize the number of eligible bidders that we got. That encourages competition and results in lower costs. The other great advantage of a series of smaller contracts is that there is more opportunity for minority and disabled business enterprises to participate. Dividing up the project into smaller contracts enhances diversity and opportunity for all Californians.”

Evidently, the strategy is working. In addition to successfully employing a diverse range of contractors and companies, Caltrans can point to the fact that the skyway bridge is 73% complete and ahead of schedule.

Bridges epitomize strength, providing vital transportation links. But that’s only if those bridges remain standing, so Caltrans is making sure they do. By applying the latest seismic knowledge and advanced technology, Caltrans’s TBSRP gives California’s bridges their best chance to withstand the considerable forces of nature. For Caltrans and Randell Iwasaki, there’s no such thing as a bridge too far.