The Labor Day Bay Bridge celebration for the opening of the eastern span may be postponed. In the last few weeks, concern about issues with the Self Anchored Suspension Span (SAS) of the San Francisco-Oakland Bay Bridge, and specifically the cracked anchor bolts, has greatly increased from Governor Jerry Brown’s enlightened comment on May 7, 2013, that “shit happens.” Indeed, the problems with the bolts have heightened concern about public safety and a real possibility that the SAS will not be ready for use until 2014. After all, we are talking about the structural integrity of the state’s most traversed bridge, and at a cost of $6.4 billion, the largest public works project in California history.
In mid-March 2013, after introducing stress meant to simulate the lateral motion of a large earthquake, 32 of 96 anchor bolts manufactured in 2008, snapped. The bolts were embedded in the concrete of the East pier (E2) and were 3 inches in diameter and varied between 9ft and 24ft long. The broken bolts were meant to connect the bridge deck to so-called shear keys – large shock absorbers designed to accommodate earthquake movement.
Affected Anchor Bolts Pictured Below:
An April 24, 2013 presentation from the Toll Bridge Oversight Committee (TBOC), comprised of the Director of Caltrans, and the Executive Directors of the California Transportation Commission and the Bay Area Toll Authority, explained that the seismic stabilizing bolt failures are attributed to hydrogen embrittlement. Apparently, excess hydrogen in the bolts caused the threaded areas to become brittle and fracture under high tension. It is unclear whether the excess hydrogen came from internal (related to the steel production) or external sources (cracks in the steel exposed to rainwater). Additionally, the bolts were made from a galvanized steel that is very hard and prone to cracking. Notably, current Caltrans Bridge specifications do not allow the use of the same galvanized bolts for standard bridge applications.
Two potential “fixes” to the broken rods in the shear keys include adding a steel collar or steel saddle. At the May 8th presentation, TBOC recommended using the steel saddle, which provides an equivalent clamping force as the original bolt design, but with a price tag of only $5-$10 million for the public (which is on top of current price of $6.4 billion – more than four times the original contract amount).
A diagram of the steel saddle fix with cable and saddle system to secure shear keys to the beam is included below. Click here for pictures of crews preparing concrete cap beam for the steel saddles.
Unfortunately, the problems with broken bolts in the shear keys are not the only issues Caltrans faces. The safety of more than 1200 additional threaded bolts manufactured in 2010 and installed on the bridge, has been called into question because they were made to similar specifications, including the use of galvanized steel. Most troubling are the 400 bolts at the base of the suspension bridge tower, critically important for stability during an earthquake. Although these bolts have not shown any signs of failure yet, their location — embedded within concrete at the base of the tower — make them particularly hard to examine.
Caltrans officials haven’t reached a decision about what to do with the suspect bolts, but said they would be putting extra bolts from the same shipment through rigorous destructive testing. Caltrans will announce whether these bolts need to be replaced at a special meeting with the Bay Area Toll Authority on May 29th.
Certainly, the public wants a bridge that can safely withstand a seismic event. And it is beyond dispute it should be done right and not be rushed at the expense of safety. However, the disturbing reality may be that California’s transportation officials will be forced to choose the lesser of two evils. Bay Area Toll Authority’s Steve Heminger says they have to weigh the risks to the public of opening the new span with some uncertainties to the risks of leaving traffic on the old steel truss span. The old truss has little uncertainty about it. It will collapse in a big quake. However, it is unclear from the information currently available, whether the new SAS span provides the public with much, if any, additional security. In the coming weeks, hopefully the TBOC and other transportation officials can rebuild the public’s trust and provide assurances to the public that it is not trading in an old defective bridge for a very expensive new and equally defective one.
For additional information on the matter, see:
Metropolitan Transportation Commission – Bay Area Toll Authority Briefings on Bay Bridge East Span Bolt Issue: http://mtc.ca.gov/news/current_topics/4-13/sfobb.htm
Bay Bridge Seismic Safety Project Website: http://baybridgeinfo.org/
May 15, 2013, ENR report summarizing the California Senate Panel Grills Caltrans About Bay Bridge Broken Bolts: http://enr.construction.com/yb/enr/article.aspx?story_id=185648991