When recent tests revealed rust and tiny cracks on one of the massive steel rods that secure the tower of the new San Francisco-Oakland Bay Bridge to its foundation, bridge officials expressed concerns that other rods might be cracked, raising questions about whether the tower would be vulnerable in a major earthquake.
Caltrans’ chief engineer for the span, Brian Maroney, said earlier this month that even if the 422 remaining anchor rods didn’t exist, the tower would easily survive even the most extreme quake.
Some experts in civil and metallurgical engineering dispute Maroney’s conclusion. They say corrosion and cracking in the 26-foot-long rods might place the span at risk.
The following questions and answers describe the controversy and its background.
Q: Why are the rods needed, and how were they contaminated?
A: These rods help anchor the tower during a large quake, which can cause dramatic upward and lateral motions. They are similar to others that snapped in 2013 on the eastern pier of the suspension span, requiring a costly retrofit.
Installed in 2007, the rods begin a few feet above the base of the tower footing, near the water line. They descend into the reinforced concrete foundation cap.
The space around the rods was meant to be filled with grout, a cement-like paste to protect against corrosion and cracks caused by moisture. But before grouting in 2011, the space was not well sealed against rain or wash water from construction, and nearly all rods were exposed to water.
Q: How much did the rods cost?
A: The California Department of Transportation has not yet provided an estimate for the cost of the rods’ design, manufacture and installation, saying the calculations involve multiple contracts. But by all accounts, the price tag ran into many millions of dollars. Work to address concerns about water and corrosion in the rods since last fall has cost tens of thousands of dollars.
Q: When was the problem discovered?
A: In 2013, following the fracturing of the rods on the eastern pier, Bill Casey, a top Caltrans engineer for the project, began a general review of the bridge. As part of that process, he extracted one anchor rod from the tower base.
Casey explained what happened at a March 5 meeting of the Toll Bridge Program Oversight Committee, a panel created by the Legislature to approve major construction and spending. When he pulled the rod out, it was wet and water had collected at the bottom of the hole, Casey said. He did not alert higher ups, even though water contamination was one reason the east pier rods fractured.
Casey told The Sacramento Bee that he considered the water unremarkable, left over from the normal grouting process, which requires the use of some moisture. He and Maroney still maintain that this type of water was not harmful to the rods. Nevertheless, they now plan to order a full battery of tests.
Yun Chung, a retired metallurgist who has written extensively about the anchor rod issue, said that explanation seems to reflect a misunderstanding of grout chemistry. “The whole purpose of the grout is to keep water away from the rods,” which are inherently vulnerable to corrosion-related cracking, Chung said. Water – no matter its source – is the enemy of the steel, he said.
In an interview, Robert Bea, engineering professor emeritus at UC Berkeley and an expert in risk assessment, called Casey’s failure to respond to the water problem in 2013 “egregious” and “unacceptable”
Last fall, Casey noticed standing water in spaces surrounding a few tower base rods during a routine inspection. Looking further, Caltrans found that 151 rods were not fully grouted – a serious construction lapse. In six cases, little or no grout was present. Wherever grout is missing, the rods are vulnerable to corrosion.
At that point, Caltrans realized it had a problem, and a second rod was extracted for rigorous testing. Experts recently detected corrosion and minute cracks at the bottom of that rod. Further testing will be conducted to determined if cracking also occurred at the top.
Q: What caused the cracks?
A: Caltrans says it is not yet clear why cracks occurred, but a manufacturing step might have played a role. The rods were treated in hydrochloric acid before being covered in molten zinc to protect the steel against corrosion. Acid can cause hydrogen to enter the steel of such rods, inducing brittleness and vulnerability to cracking under stress.
Maroney said at the recent meeting that Caltrans does not know if the acid bath was long enough to be a problem. Quality assurance records for the job – including inspection records that could settle the matter – have not been located.
In an interview, Maroney said he will seek funds for tests to determine whether the cracks were caused during manufacturing or by corrosion. He said the rods might have been harmed when Caltrans pulled the tower 18 inches to one side for one year to move the span off temporary supports and “load” it onto its cable. That process stressed some rods dramatically. “If it’s stress corrosion cracking you need to have a sustained load for a long time,” he said. “One year is a long time.”
Q: How many rods might be at risk?
A: Caltrans does not know how many other rods might be corroded or cracked. Definitive tests require removal of the rods – a destructive process.
Q: Why not replace the rods to ensure safety?
A: Putting aside the astronomical cost of rod replacement, they are embedded in the foundation cap, making installation of new rods impossible.
Maroney said he has devised methods to retrofit the function of the rods if needed, such as adding steel beams between the tower and its base. “I have some tricks up my sleeve from 25 years of modifying bridges,” he said
But Bea, the UC Berkeley professor, criticized the state’s design choice. “One of the basic, fundamental principles involved in engineering a structural system is to engineer explicitly for repairability,” in case unforeseen problems arise, he said. In marine environments, moisture-related damage and repairs over time are typical, Bea said.
Q: Is public safety at risk?
A: Maroney said at the March 5 meeting that even if other rods have tiny corrosion-related cracks, similar to what has been found in the tested rod, they would remain sound for more than 100 years. Yet in the same meeting, he conceded that some rods might already be fractured all the way through.
Asked about that apparent contradiction, Maroney said the most likely risk is long-term: small cracks growing over many years. But to be sure, he plans to use high-frequency sound waves to check each rod for fractures between now and the next oversight committee meeting, on April 17.
Caltrans previously described the rods as important to secure the tower in a large temblor. But Maroney said computer modeling shows that even if all the rods were missing, the tower would move no more than one-third of an inch upward in the largest anticipated quake. It might lean slightly, but with no impact on bridge traffic and no safety risk.
Bea disagreed. “I find such statements to be alarming and not credible,” he said.
“In a very strong earthquake, we’ve learned through sad experience that the vertical motions can be equal to if not greater than the horizontal motions.” This makes a secure connection between the tower and the foundation vital.
Q: If the rods were unneeded for seismic safety or to ensure post-quake traffic flow, why were they installed and why should more time and money be spent on research about them?
A: Although they are not a critical safety feature, Maroney said, the rods would offer an extra measure of support for the tower following an earthquake.
Q: What happens now?
A: Efforts to understand this problem are a work in progress that could take months to complete. Maroney said he wants thorough testing to ensure that nothing has been overlooked, and to predict whether tiny cracks in the rods could grow perilously over a short or a long period. He believes such tests, if approved, will cost a few million dollars.
For now, Maroney proposes leaving the rods ungrouted but using dehumidifiers to keep them dry – and therefore, free from further corrosion. The absence of grout would allow easier monitoring for future problems over the span’s anticipated 150-year service life.
Until recently, Caltrans has said that tension in the rods was too low to prompt cracking. Now that cracks have occurred, Maroney said lowering that tension further, by loosening the nuts that secure the rods, might be an option to reduce the risk of more cracking over time.
Charles J. McMahon, Jr., professor emeritus of materials science and engineering at the University of Pennsylvania, said that with so many unknowns about the state of the rods, Maroney’s comments amounted to guesswork.
“If you’re the person responsible for having this mess occur in the first place, you want to minimize the problem. … That’s human nature,” McMahon said.
Given the litany of problems on the new span revealed in recent years, he said, “I think this may go down as the greatest civil engineering screw-up in the history of the United States.”
Call The Bee’s Charles Piller, (916) 321-1113. Follow him on Twitter @cpiller.