Case Study: Bay Bridge Bolt Failure

Also known as the San Francisco-Oakland Bay Bridge, the east section of the Bay Bridge collapsed in 1989 as a result of earthquakes in the area. The decision was eventually made to replace the entire bridge with a more earthquake resistant structure, with the western portion begining construction in 2004. In 2013 the eastern section of the new bridge was completed. However, construction did not go as planned. When pre-tension was applied, before finalization of construction, 32 of 96 A354BD bolts fractured within two weeks.

The bolts that failed were placed in 2008 as part of the shear keys meant to increase seismic resistance, meaning they did not contribute to the structure of the bridge. After the failure, all 96 bolts in the shear keys were considered suspect and alternative anchors were devised. However, the A354BD bolts were used in other places of construction so a detailed metallurgical analysis was conducted to ensure the bolts throughout the bridge would not fail as well. The failure was ultimately determined to be a result of hydrogen embrittlement. It was also eventually concluded that this was a result of the environment the rods were subjected to (seawater), not the manufacturing process, and the bolts used elsewhere throughout the bridge were allowed to remain supplemental corrosion protection measures.

Sources/Further Reading: (Images source - Structure Magazine) (TBPOC Report) (TWI Presentation)