California Department of Transportation
Date: Feburary 20, 2015
District: 4 - Oakland
Contact: Leah Robinson-Leach
Phone: (510) 715-6730
Caltrans Updates Public on Continuing Bay Bridge Tower Anchor Rod Grout Assessment
OAKLAND—Caltrans today provided another status update on the ongoing assessment of corrosion-protecting grout around the tower anchor rods and testing on one rod from the Bay Bridge tower foundation.
Underneath the Bay Bridge deck, there are 152, 6-inch solid steel dowels that prevent the 525 foot steel tower from sliding atop a massive steel and concrete foundation. There are also 424 high-strength steel anchor rods—each about 25 feet long—that also link the foundation and tower for additional seismic performance during an earthquake. Last year, one of these anchor rods was subjected to extensive laboratory testing, including soaking it in salt water for extended periods of time and then stressing to failure, a test that helped confirm the anchor rod's strength.
These 424 anchor rods are surrounded by long steel tubes that are supposed to be filled with grout to prevent water from contacting the steel rods. Unfortunately, the state's contractor failed to properly fill all the 424 tubes with grout. In September 2014, Caltrans inspectors observed water at the base of the SAS tower beneath caulking that was placed around the rods. A quarter of the tubes were not fully grouted, with several other tubes missing inches to meters of grout.
The state's contractor took responsibility for the errors and agreed to work with Caltrans to fix this problem. Since then, contractors have drilled inspection holes in the existing grout, to thoroughly investigate grout and anchor rod conditions. Tiny cameras called borescopes are being used to help evaluate the grout conditions.
Workers also removed one of the 424 anchor rods that was not properly grouted in order to conduct extensive laboratory testing including visual inspection, examining the galvanization and mechanical testing. The purpose of the testing is to determine whether any of the corrosion-protective galvanization on the rod was compromised and, if so, to what extent. Removing the anchor rod for testing took nearly a month and involved hydraulic torque wrenches and 100-ton jacks.
One preliminary test result shows some galvanization is missing around the threads at the bottom of the anchor rod, leading to potential corrosion of the steel of this one bolt. Powerful scanning electron microscopes providing 1000-times magnification show a microscopic crack in the anchor rod material. It is too early to develop conclusions about the cause or significance of this observation without additional tests and analysis.
"We have one preliminary test result that shows a microscopic indication on the surface of the steel of one bolt," said Dr. Brian Maroney Chief Bridge Engineer who ordered extensive bolt testing on the Bridge. "Given the tremendous forces applied to the rod to remove it for testing, it is too early to determine exactly what this means and we are ordering additional testing. Regardless of what we discover about the past, we will take whatever steps are necessary to protect the rods from corrosion going forward."
For background on the ongoing review of the Bay Bridge anchor rod grout, please see this recent Caltrans News Flash: https://www.youtube.com/watch?v=AjMhuFUIwPQ&feature=youtu.be