The opening of the San Francisco–Oakland Bay Bridge on Labor Day 2013 marked the symbolic end of a long and challenging journey.

On September 2, 2013, the new San Francisco–Oakland Bay Bridge opened to traffic. The opening celebration was a long-awaited event, as planning for the new bridge began more than two decades ago when a span of the old bridge failed during the 1989 Loma Prieta earthquake. The new Bay Bridge, as it is known locally, is the result of several phases of work using state-of-the-art seismic technology to retrofit the west side of the bridge and construct a new east span. The new bridge carries I–80 and more than 280,000 vehicles daily between Oakland and San Francisco and is now equipped to withstand the shaking associated with an earthquake seismologists expect to occur only once every 1,500 years.

After a lengthy study and environmental review process, the California Department of Transportation (Caltrans) began constructing a new east span of the bridge in 2002. Several contracts and more than a decade later, the new bridge opened to traffic following the inaugural celebration held on Labor Day 2013. For those working on the project, it was a race against time to move traffic off the existing structure and onto the new seismically superior bridge.

“The Bay Bridge team of architects, planners, designers, and builders deserve all the recognition for achieving this tremendous accomplishment,” says Andre Boutros, executive director of the California Transportation Commission. “It was achieved through true partnerships, hard work, and determination. It’s fitting that the new Bay Bridge opened to traffic on Labor Day, symbolizing the contributions of the thousands of people who have labored tirelessly for years to provide not only a safe bay crossing, but an iconic structure that can be celebrated for generations to come.”

A previous article, “Bridging the Bay” in the September/October 2012 issue of Public Roads, details the history of the original Bay Bridge, the damage caused by the Loma Prieta earthquake, and planning and construction of the new east span through February 2012. Here is the rest of the story.

Construction Continued After the Cable Installation

From the time the cable catwalk was installed in June 2011, it took Caltrans’ crews nearly 12 months to thread and compact the 137 strands of suspension cable, each 1 mile (1.6 kilometers) long, for the bridge’s signature span. During that time, the overall look of the suspension span appeared relatively unchanged. But after the cable installation, the visible changes became much more dramatic. Among the more noticeable changes were the installation of the cable clamps and suspender ropes, load transfer to the cable, and removal of the falsework.

By August 2012 Caltrans had installed the tower finials and by June 2013 it had removed the tower crane, along with the network of scaffolding, revealing the self-anchored suspension (SAS) span tower. The SAS span is the signature section of the bridge and features one continuous suspension cable and two anchorage points built into the east end of the superstructure. Shortly after the bridge opening, a pyramid-shaped skirting at the base of the tower added a sense of visual stability to the slender four-legged tower.

Concurrent with installation of the tower finials and crane removal, Caltrans positioned and connected the two other major spans of the new east side, the Skyway and the Yerba Buena Island Transition Structure, to the SAS signature span. Modular expansion joints connected the 2,047-foot (624-meter)-long SAS span to the approaching structures.

Crews coated the suspension cable with a zinc rich paste, wrapped the cable with S-wires (interlocking flat wires with an “S” cross section), and then painted all the steel white. The detailed shroud covering the cable that wraps around the west end of the SAS highlights the complexity of the design. The path the suspension cable takes from widest apart at the anchorages to the narrowest at the top of the tower creates multiple “X” patterns in the suspender ropes when viewed from the side. The removal of the suspension cable catwalks revealed the graceful catenary lines. The appearance improved even more when crews removed the construction materials from the deck and applied an epoxy-asphalt wearing surface to the deck.

The work has continued after the grand opening celebration. Construction crews immediately began dismantling the old 1936 steel cantilever truss structure. Workers will remove the concrete decks and take the steel truss apart piece by piece. By 2017, the old structure will be completely gone and only the new bridge will grace the bay area skyline between Oakland and Yerba Buena Island.

“For 75 years, the Bay Bridge has been the proud workhorse of the bay area transportation network, and it has been fully rebuilt to remain the bay area’s most important highway structure,” says Steven Heminger, executive director of the Metropolitan Transportation Commission for the San Francisco Bay area. “In addition to its economic importance, the new bridge allows bicycle and pedestrian access to spectacular views of the bay, and the new east span is well on its way to taking its rightful place alongside the Golden Gate Bridge as a man-made wonder of the San Francisco Bay area.”

The Eleventh-Hour Challenge

Like most large bridge projects, the opening of the new Bay Bridge did not come to pass without challenges. Arguably the biggest hurdle came in March 2013. After tensioning the masonry plate anchor rods on two of the shear keys (devices that resist seismic loads) on the east main pier (Pier E2), some of the rods fractured. The anchor rods are 3 inches (7.6 centimeters) in diameter with an ultimate tensile strength of 140,000 pounds per square inch (9,843 kilograms per square centimeter). The discovery of the fractured rods started a firestorm of concerns about the quality of the material because the SAS contained more than 2,300 fasteners of the same material.

Pier E2 is near the east end of the SAS and has four bearing assemblies that enable the span’s longitudinal and rotational movements. The bearings are designed to tolerate transverse movements and to restrain uplift forces exerted upon the structure, such as seismic events. The four shear keys engage transverse and longitudinal movements during seismic events. In an extreme seismic event, for example, the shear keys will absorb the movements before engaging the bearings, minimizing potential damage to the bearing assemblies.

To anchor the bearing assemblies, more than 190 masonry plate anchor rods extend full length through the Pier E2 cap for bearings B1 through B4 and the S3 and S4 shear keys. S3 and S4 reside at the middle of the cap connecting to the superstructure crossbeam and are designed to engage only transverse movements.

The S1 and S2 shear keys, however, reside over the Pier E2 columns where full-length anchors are not possible because of the pier’s columns. In 2008, the 96 masonry plate anchor rods of these two shear keys were embedded in the cast-in-place concrete cap of Pier E2. It was these rods that failed shortly after tensioning in March 2013.

Caltrans later installed the Pier E2 bearing and the S3 and S4 anchor rods, after positioning the SAS over Pier E2, and fully tensioned them by April 2013. Altogether, the crews installed and tensioned more than 540 rods, which were manufactured in 2010, to connect the four bearings and four shear keys to the cap and the superstructure. To obtain a proper clamping force for the bearings and shear keys, Caltrans tensioned the rods to approximately 70 percent of the ultimate tensile strength. In addition, to minimize dirt and debris carried by deck drainage and extend the life of the rods, an in-span expansion joint was installed to the east of Pier E2.

Identifying the Problem and a Solution

Immediately after the rod failure, the Toll Bridge Program Oversight Committee, consisting of executives from the Bay Area Toll Authority, Caltrans, and the California Transportation Commission, began investigating the cause of the problem. In July 2013, the committee produced a draft report summarizing its findings: Report on the A354 Grade BD High-Strength Steel Rods on the New East Span of the San Francisco–Oakland Bay Bridge With Findings and Decisions.

Span Locations and Schedule of Replacement

 The masonry plate anchor rods for the S1 and S2 shear keys, the ones that failed, were manufactured in 2008. Because S1 and S2 reside directly over the Pier E2 columns, the masonry plate anchor rods had to be in place when Caltrans cast the Pier E2 cap in 2008, leaving them exposed to the bay area’s weather until their final fit up in 2013. The full-length masonry plate anchor rods for the bearings and shear keys S3 and S4 were manufactured in 2010 and protected from the effects of weather until their installation in 2013. None of the tensioned anchor rods manufactured in 2010 have failed.

Caltrans accepted the rods manufactured in 2008 based on the contract requirements, because they met strength, averaged elongation, and hardness limits. However, after the failures, studies of samples revealed that the values for those limits were significantly different than those of the 2010 rod samples. In the end, the committee investigating the failed rods determined that hydrogen embrittlement was the culprit. Hydrogen embrittlement is a process by which susceptible metals become brittle and may fracture after tensioning because of exposure to hydrogen during the manufacturing process or through environmental factors. Caltrans continues to test the population of similar rods and bolts throughout the SAS to assess their susceptibility to stress corrosion cracking for long-term maintenance requirements.

In total, 32 of the 96 S1 and S2 masonry plate anchor rods failed before Caltrans released the tension in the remaining rods and began to explore alternatives to replace the lost clamping force. The final decision was to use post-tensioning saddles with anchorages cast in a new reinforced concrete “blister” surrounding the Pier E2 cap at the column locations.

FHWA Reviews Anchor Rod Issues

Shortly after failure of the anchor rods, the Toll Bridge Program Oversight Committee asked the Federal Highway Administration (FHWA) to perform an independent review of the construction documentation and the committee’s strategies concerning the disposition of the rods that failed. FHWA accepted the request for review and convened a team of bridge experts from its headquarters, Resource Center, the Turner-Fairbank Highway Research Center, and the California Division Office. FHWA’s Myint Lwin, then director of FHWA’s Office of Bridge Technology, led the review team.

The team performed field reviews, observed test results, and reviewed the analysis of the sampled rods from the 2008 and 2010 fabrications. The team members also consulted with technical experts directly involved in evaluation of the rod failures, reviewed full sets of construction documentation, and studied the oversight committee’s report on the affected rods and bolts. The FHWA team reported its findings to the Bay Area Toll Authority on July 10, 2013, concluding that the retrofit work described in the oversight committee’s Report on the A354 Grade BD High-Strength Steel Rods on the New East Span of the San Francisco–Oakland Bay Bridge With Findings and Decisions would allow for the safe operation of the new bridge.

At first, the projected completion date for retrofitting the S1 and S2 shear keys fell nearly 3 months after the desired Labor Day opening of the new bridge to traffic. But because of concerns related to the old bridge’s ability to withstand seismic events, the project’s peer review team proposed to shim the Pier E2 bearings temporarily. More specifically, they proposed to reduce the size of space allowed for transverse and longitudinal movements of the bearings by installing shims, which would engage seismic forces in place of the S1 and S2 shear keys until the permanent retrofit could be completed. While the solution posed some risk of bearing damage during an extreme seismic event, it ensured the safety of the superstructure and traffic using the bridge. As soon as the retrofit achieves an adequate clamping force on shear keys S1 and S2, the bearing shims would be removed. This temporary measure enabled Caltrans to safely open the new bridge before completion of the retrofit. Upon request, FHWA once again performed an independent review of the proposal and the retrofit design.

 On August 15, 2013, FHWA California Division Administrator Vincent Mammano reported to the oversight committee that the FHWA review team found that installing the temporary bearing shims would be a viable and safe solution, enabling Caltrans to open the bridge to traffic before completing the retrofit of the S1 and S2 shear keys. After reviewing the design plans, the team confirmed that the clamping force from post-tensioning would adequately replace the clamping force of the S1 and S2 shear key masonry plate anchor rods. The oversight committee, after weighing the high seismic risks associated with the old bridge, decided to move forward with installing the bearing shims and to open the new bridge on Labor Day 2013.

The S1 and S2 retrofits progressed quickly with the west face of the shear key S2 retrofit the last to be cast. Soon after casting, Caltrans will push the strands through the ducts. Each of the post-tensioned saddles has three rows of five ducts with anchors at each end totaling 30 anchors. The strands will be tensioned at the anchors to provide a clamping force on each side of the shear key. Each of the four saddles for the S1 and S2 shear keys has three sections, and to properly fit up the saddles, all the exposed 2008 rod ends have been removed.

“FHWA also noted that after the anchor rods failed, the project office, the designer of record, and the contractor worked together to find a solution to replace the clamping force of the Pier E2 shear key anchor rods,” says Mike Duman, the chief operating officer of the FHWA California Division Office. “They all put their heads together to find the least complex option that would be both constructible and economically feasible, while meeting scheduling expectations.”

In addition to completing the retrofit work, crews also are working to complete other smaller tasks on the bridge. These tasks do not interfere with the inservice bridge, but include installing an elevator and dehumidification systems, spot painting, and sealing drainage issues.

Ongoing Risk Mitigation

The State continues to test samples made from the same type of materials that failed to determine the risk of long-term failure and to improve specifications and testing for future materials.

As recommended by the FHWA review team, Caltrans advanced enclosures for many of the SAS fasteners so dehumidification and temperature control can help to ensure longer life. The review team also recommended advancing the construction of the skirting around the T1 tower base to facilitate dehumidification. Other elements, such as the Pier E2 anchors, remain exposed to the marine elements, which raises the risk of cracking due to stress corrosion. However, a multidisciplinary team of experts is developing requirements for regular maintenance and inspection for the bridge, including these fasteners, to help minimize the risk of failure.

Caltrans maintenance will assume responsibility for keeping the Bay Bridge safe through compliance with the requirements outlined in the National Bridge Inspection Standards and scheduled maintenance activities.

“We encountered many challenges during construction of this monumental structure,” says Malcolm Dougherty, director of Caltrans. “But the entire Bay Bridge team stayed focused on the main goal of the project, seismic safety for the 280,000 daily travelers on the Bay Bridge. Moving traffic from the seismically deficient existing bridge was a clear engineering decision when construction of the new Bay Bridge was ready. But it took collaboration and teamwork . . . to demonstrate to the public that the time to move traffic to a much safer bridge had come. Any one entity could have delayed opening for months, but, with a clear goal of seismic safety, engineers found solutions, overseers sought second opinions, and experts from FHWA and other engineering firms agreed. On Labor Day 2013, it all culminated in the opening of a state-of-the-art bridge that has captured the confidence and admiration of bay area travelers.”

Greg A. Kolle is a bridge engineer with the FHWA California Division Office. Since 2008, he has served as the major project oversight manager for the project to replace the east span of the Bay Bridge. Kolle worked as a bridge engineer for the Washington State Department of Transportation prior to joining FHWA. After serving in the U.S. Air Force from 1972 to 1976, Kolle received his B.S. in civil engineering from North Dakota State University at Fargo.

For more information, visit baybridgeinfo.org or contact Greg Kolle at 916–498–5852 or greg.kolle@dot.gov.

The author would like to thank all those involved in the seismic replacement project of the San Francisco–Oakland Bay Bridge East Span for their dedication to provide a safe bridge for all users.