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San Francisco Bay Bridge- How a landmark became a a debacle

 
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Dr. N. Subramanian
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PostPosted: Fri Jul 24, 2015 6:19 pm    Post subject: San Francisco Bay Bridge- How a landmark became a a debacle Reply with quote

San Francisco Bay Bridge- How a landmark became a a debacle


Back Story
As the second busiest bridge in the USA, the San Francisco Bay Bridge carries 270,000 cars each day between Oakland and San Francisco. The bridge was first built in 1936. In 1989, a 6.9-magnitude earthquake hit the Bay Bridge, killing a motorist and causing part of the deck to buckle. A design was proposed for a new span, and after years of political and engineering debates, it was finally built alongside the old one to replace the damaged 2.2 miles that stretch east toward Oakland.


One of the largest public works projects in the United States, the construction of the eastern span of the Bay Bridge was 10 years late and $5.2 Billion over budget. The new east Bay Bridge span opened on Sept. 2nd, 2013.

Many of the problems are linked to the bridge’s unusual complexity, according to a panel of engineers that looked at the project last summer for the state Legislative Analyst’s Office.

Their report concluded that Caltrans engineers had warned at the time that the bridge would be a technical nightmare. The design panel chose the configuration, the report said, because of “aesthetics” and “without a full appreciation” of its challenges.

All but one of the bridge experts on the selection panel opposed the final design, but they were outvoted by those with no bridge knowledge or experience.

In March 2013, when it seemed that the new span was well on its way to completion, until workers tightened 32 steel bolts that were intended to stabilize the bridge during an earthquake and discovered the bolts were brittle, and cracked.


For a bridge built between two major earthquake faults, the failure of the bolts placed the entire seismic safety system of the new span into question. The 32 bolts that failed were among 96 bolts that were delivered in 2008. After the bolts were installed, they were covered by the bridge roadways and are no longer accessible to remove or replace. The California Department of Transportation (Caltrans) devised a plan to add a metal saddle or collar around the seismic-stability structures to do the bolts' job.


For an interactive graphic highlighting the issues of the bridge, visit the following link and clivk on the dotted areas.
http://www.sfchronicle.com/local/item/Troubled-Bay-Bridge-36359.php

Bolt Failure -Cause of Failure

The bolts’ hardened, galvanized steel had been contaminated by hydrogen, which caused them to become brittle and crack. The bolts were contaminated either during manufacturing or from being left in holes that filled up with rainwater.



Hundreds of documents released by Caltrans show its inspectors found structural integrity issues with some of the bolts years before they were installed. Inspectors said bolts made by Painesville, Ohio-based Dyson Corp. had failed to meet certain standards during testing on three occasions. In addition, the contract called for bundles of high-strength wire under tension to be grouted within a 30-day period to protect them from corrosion, but they were left exposed for 15 months and were severely corroded.


Cost of Failure
The projected cost overrun due to corrosion issues that occurred before the bridge was even built was $23 million. Caltrans may try to replace 736 of the 2,200 rods, the ones at greatest risk of cracking, depending on the outcome of tests. To pay for the bridge’s construction, a higher toll of $6.00 per car was adopted.





Conclusion
The Caltrans mistakes made headlines. In a televised interview that aired nationwide, a UC Berkley materials science and engineering professor bluntly criticized Caltrans for generalizing engineering knowledge required for the bridge work, and not employing metallurgical and corrosion expertise. Many others agreed, noting the corrosion occurred quickly making the problem, and public safety risk evident before the bridge was completed which gave Caltrans time to make sufficient repairs. In this case, Caltrans did have a written corrosion plan, but executed it without qualified personnel.

References:

  1. Chung, Yun, Lisa K. Thomas. High Strength Steel Anchor Rod Problems on the New Bay Bridge, Rev 1. Prepared for Sena-tor Mark DeSaulnier. 12 Nov. 2013. Committee on Transportation and Housing California State Senate. Retrieved 26 Mar. 2014 from http://media.sacbee.com/smedia/2013/12/07/21/47/Djfhs.So.4.pdf
  2. Van Derbeken, Jaxon. “Bay Bridge Fasteners Withstand Tests, Caltrans Says.” SFGate. Hearst Communications, 25 Aug. 2013. Web. 26 Mar. 2014. http://www.sfgate.com/bayarea/article/Bay-Bridge-fasteners-withstand-tests-Caltrans-4760330.php.
  3. Vorderbrueggen, Lisa. “Cascade of Poor Decisions Led to Broken Bay Bridge Bolts, Oversight Panel Says.” MercuryN-ews.com. San Jose Mercury News, 9 July 2013. Web. 26 Mar. 2014. http://www.mercurynews.com/ci_23629435/cascade-poor-decisions-led-broken-bay-bridge-bolts.
  4. Woodruff, Judy. “Broken Bolts Is Latest Woe for Late, Over Budget and Earthquake-Prone Bay Bridge.” PBS. PBS, 12 Aug. 2013. Web. 26 Mar. 2014. http://www.pbs.org/newshour/bb/nation/july-dec13/bridge_08-12.html
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- See more at: http://www.nace.org/CORROSION-FAILURES-San-Francisco-Bay-Bridge-Bolt-Failure.aspx#sthash.qTOf1DdS.dpuf
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