SACRAMENTO — The eastern span of the San Francisco-Oakland Bay Bridge will not open as scheduled on Labor Day as it will take contractors until at least December to repair cracks in the bridge's seismic safety bolts, the Toll Bridge Program Oversight Committee announced Monday.

A new opening date for the $6.4 billion crossing will be decided after the retrofit of the failed bolts is completed, which is estimated to take until at least Dec. 10, the committee said in a report. The report said a new date will be based upon "actual completion of the east pier retrofit work, weather windows, traffic impacts and other information."

The report lists "hydrogen embrittlement" as the root cause for why 32 seismic safety bolts cracked after being tightened in March. The problem is considered a short-term phenomenon that occurs in metals when certain conditions apply. In the case of the rods on the Bay Bridge, the report said the "metallurgical condition of the steel was found to be less than ideal."

The bridge is replacing the span damaged during the 1989 Loma Prieta earthquake, and the new project is already years late and billions over budget.

Monday's report indicates that officials overseeing the project altered the original plan for treating the high-strength steel rods on the span. Initial bridge specifications required the rods to be mechanically galvanized, subjecting them to less heat and potential embrittlement than a method called hot-dip galvanizing in which the steel is "dipped into a bath of molten zinc at approximately 850 degrees Fahrenheit."

But contractors and Caltrans design staff determined that the 3-inch and 4-inch diameter tower rods being used were "too long and too heavy for the mechanical process." The decision was based partly on Caltrans' experience with the retrofit of the Richmond-San Rafael Bridge, where the hot-dip galvanizing method was used and rods were tightened under water, the report said.

"There is little documented discussion regarding the variety of applications and far higher tension levels that would be placed on some of the high-strength rods on the (Bay Bridge) and potential alternative corrosion protection methods," the report said.

The opening of the bridge has been in doubt as crews work to install the repair for the cracked seismic safety bolts — important pieces that hold a shock-absorber-like piece called a "shear key" to the bridge deck so that the structure can move safely during a quake.

Bridge officials say the bridge will not open unless it is deemed safe to do so.

However, officials also say moving traffic onto the new span is important to public safety, as the existing crossing is not considered earthquake safe.

State lawmakers were also being briefed on the investigation at a meeting with the committee in Sacramento.


Associated Press writer Juliet Williams also contributed to this report.