SAN FRANCISCO (BCN) — Raising questions about the necessity of repairing anchor rods exposed to water at the base of the new Bay Bridge’s tower, the project’s governing body approved further study of the problem Tuesday but stopped short of moving forward with repair work.
The 2-1 vote by the Bay Bridge Toll Program Oversight Committee adds over $2.8 million to the $4.3 million already approved for work on the rods. Further repair work could add over $11 million more, though some of that could be recouped from the contractor.
About a quarter of the 424 steel rods securing the base of the bridge’s 525-foot tower were exposed to bay water because of faulty grouting. Caltrans confirmed the water exposure in the rods earlier this year.
The repairs would entail de-tensioning the roughly 25-foot rods, removing the grout, re-tensioning the rods and replacing the grout with new protective material, according to bridge chief engineer Brian Maroney. The rods are designed to prevent the tower from sliding on its concrete and steel foundation during an earthquake.
But computer simulations have shown the necessity of the rods in the event of a major earthquake is uncertain; even in the absence of those rods, simulations showed the tower moving a matter of millimeters in a seismic event.
Furthermore Caltrans conducted seismic pull testing of 407 rods earlier this year and all but one passed the test, despite the exposure to bay water.
This led the committee to question whether the rods should be repaired at all.
“If we don’t need them why do we have to fix them?” committee chairman Steve Heminger asked. “Why should we replace all the grout when most of it is in OK shape? Why replace the grout where we don’t have water? Why replace the grout when we don’t need the rods?”
Maroney said that the rods should provide some added safety in the event of an earthquake. Previously performed computer simulations did not take all variables into account and he would like to conduct new simulations that better reflect the bridge construction, though the previous simulations may have been more conservative and may not have taken some of the bridge’s safety measures into account.
Such simulations were one of several steps approved by the oversight committee Tuesday. The $2.8 million approved also funds further study of the four removed rods, some of which had stripped threads and microfractures, as well as further seismic testing.
Maroney will report back to the committee monthly with updates on the progress of the investigation and make recommendations on whether the repairs are necessary. If approved, all repairs are expected to be completed by the end of next year.