Fixing Bay Bridge tower’s lean put crucial rods at risk

A crane removes a section of steel girder sliced from the old Bay Bridge span as demolition work continues in Oakland, Calif. on Thursday, March 5, 2015. The Toll Bridge Program Oversight Committee is scheduled to meet today to discuss cost overruns and potential delays in the demolition project. less A crane removes a section of steel girder sliced from the old Bay Bridge span as demolition work continues in Oakland, Calif. on Thursday, March 5, 2015. The Toll Bridge Program Oversight Committee is scheduled ... more Photo: Paul Chinn, The Chronicle Buy photo Photo: Paul Chinn, The Chronicle Image 1 of / 4 Caption Close Fixing Bay Bridge tower’s lean put crucial rods at risk 1 / 4 Back to Gallery

More than half the 400 steel rods that hold the new Bay Bridge eastern span’s tower in place were put at significantly greater risk of cracking when engineers fixed a lean in the landmark tower by tugging it into its proper position, a bridge official revealed Thursday.

The problem was that when it was first installed, the top of the tower listed 18 inches closer to the East Bay shore than it should have, project chief engineer Brian Maroney told members of a bridge oversight committee.

To pull the tower upright, workers attached high-tension cables on Yerba Buena Island to the 525-foot-tall structure for a full year in 2011 and 2012, Maroney said. One outside expert likened it to using a giant crowbar to pry the tower into place.

That did the job — but it may have endangered the galvanized, high-strength steel rods that anchor the tower to its foundation, Maroney said.

The integrity of the 25-foot-long rods had already been thrown into doubt because of another construction problem: A botched grouting and caulking job had them stewing in water for years after they were installed. One rod that was removed for testing was found to have rust and corrosion, Caltrans said.

2013 failure

Before Thursday, Caltrans had downplayed the risk from the long-term soaking, saying the rods were under less stress than 32 similar steel fasteners that snapped when they were tightened on the bridge’s seismic-stabilizer structures in 2013. Stress is a key factor in causing corrosion damage from hydrogen, the element that led to the sudden failure of those rods.

The tower was off-center after it was lifted into position in 2010 because the eastern half of the suspension span is longer than the western half, creating forces that pulled the structure eastward, Maroney said.

“Aesthetically, that's not a very good thing,” he told the oversight committee at a meeting in Oakland. “We want the tower to be nice and vertical when it's done.”

Maroney acknowledged that tugging the tower into its proper position could have put the water-soaked anchor rods at greater risk of cracking.

“We pulled them,” Maroney said. “That was a pretty significant process. ... There was a lot of force involved there.”

Tiny cracks

Maroney said the stress that the rods sustained during the year the tower was being pulled into position could account for microscopic cracks that were found on the rod that was removed from the foundation and tested. He said more tests need to be done to be certain.

The rod was taken from eastern side of the tower base, where the tension was greatest as the structure was being pulled toward Yerba Buena, Maroney said.

“When we pulled the tower back, we introduced some tension,” he said. “It was sustained for a long time, and (while the rods were) in standing water.”

Maroney said there is no immediate safety threat to the bridge, but that there could be a problem during a large earthquake — the kind the $6.4 billion bridge was designed to withstand after the 1989 Loma Prieta earthquake revealed the vulnerability of the old eastern span, a section of which collapsed.

The rods are supposed to keep the tower from heaving during a quake and possibly listing. If many rods fail, Maroney said, “it’s not going to be the Leaning Tower of Pisa, but it will be perturbed.”

No obvious sign

Steve Heminger, executive director of the Metropolitan Transportation Commission and chairman of the oversight panel, asked whether some rods may have already failed in their sleeves at the base of the tower. Because of the way they were installed, they would not pop out of position like the ones that failed on the seismic-stabilizer structures in 2013.

Maroney acknowledged it was a possibility and said checking for any significant cracks would not be difficult.

But it is impossible to replace any damaged rods. The fasteners were installed before the tower was put on top of them, and now there is no room to maneuver new ones into place.

Heminger said he would be more comfortable if he knew that no rods had actually failed. “I hate to say this, but for some of us it feels like a trip down memory lane,” he said, referring to the 2013 failure.

Bernard Cuzzillo, a Berkeley-based mechanical engineer who investigates material failures, said the process of yanking the tower into place may indeed account for the tiny cracks that Caltrans has identified.

'500-foot crowbar’

“This would provide additional loading on the rods, during the time they were the most vulnerable — a high hydrogen environment in water,” Cuzzillo said. “This could have put cyclic stresses on the rods, which may have resulted in crack growth or crack initiation.

“By pulling on a tower like that, it’s like a 500-foot crowbar creating a massive pulling force on these rods, which are basically like nails,” Cuzzillo said. “The material responded by cracking instead of stretching.”

The fact that Caltrans does not know whether any rods have failed is troubling, Cuzzillo said.

“If you are unable to verify the clamping force, you would basically have no information on what the tower would do in a quake,” Cuzzillo said. “It's in a quake that you need the clamping force the most.”

Charles McMahon, a metallurgist and professor emeritus at the University of Pennsylvania, said Caltrans now faces a “big question mark.”

'It’s an unknown’

“If you have evidence of cracking, you have high stress and you have water, you have a problem and there is no way to rationally judge whether these cracks are going to propagate,” McMahon said. “It’s an unknown.”

He said any cracks caused by the tower-pulling operation could get worse over time.

“When you put it in bending, you can get pretty high stresses,” McMahon said. “That should raise a lot of concerns, particularly with steel that is so susceptible to hydrogen cracking.”

Noting the litany of problems on the bridge, which have also included a leaking road-deck support structure and questionable welding work, McMahon added, “Wow. This has gone from one calamity to the next. At some point, a rational person would basically condemn the thing and redo it — if it weren’t so expensive.”

Jaxon Van Derbeken is a San Francisco Chronicle staff writer. E-mail: jvanderbeken@sfchronicle.com