Archive for the ‘San Francisco-Oakland Bay Bridge’ Category:

The Wrong Way to Sample Materials

Bay Bridge BoltsNorthern California residents are well aware of the latest glitch regarding the new east span of the San Francisco-Oakland Bay Bridge. The project was already years behind schedule and billions of dollars over budget (the latter can be blamed partially on former Governor Schwarzenegger, who ordered a major redesign to incorporate a signature design element) when bolts began snapping in March 2013 during final stressing. There is concern that hydrogen contamination during or after manufacturing might have made the bolts – some of which are roughly 30 feet long – brittle. Some critics believe that Caltrans specified the surfaces of the bolts to be too hard, which in term makes them more susceptible to breaking.

Remarkably, bolts failed back in 2008 as samples were being tested but Caltrans averaged the results. If one sample failed, it was deemed okay as long as another bolt exceeded the specifications for the elongation tests. Which means that essentially 50% of all samples might have failed the tests. UC Berkeley engineering professor Thomas Devine has criticized this method of sampling, as right he should have. Anyone familiar with Six Sigma quality control (my wife and business partner Francesca is a certified Black Belt) would find it ludicrous to allow so many failures – especially on a bridge designed to last 150 years in a seismically active area. Caltrans is now scrambling to engineer a fix for the broken bolts, a task complicated by the fact that the existing bolts are in a confined space and cannot be removed.

Caltrans is unsure whether this issue will delay the planned opening of the bridge on Labor Day weekend of this year. Other bolts manufactured in 2010 have so far held up during tensioning and a decision must be made as to whether to preemptively replace these bolts. As a California resident it will be difficult to “celebrate” this bridge opening. More likely it will seem like a relief that the worst is (hopefully) over.