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Bay Bridge Test Shows Signs of Cracking

Wednesday, February 25, 2015

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Testing has revealed tiny cracks on one of hundreds of improperly grouted anchor rods that were left to soak in water on the San Francisco-Oakland Bay Bridge, transportation officials say.

The results of ongoing, extensive laboratory testing on the rods, which are key to the seismic stability of the $6.4 billion structure, were announced Friday (Feb. 20) by the California Department of Transportation (Caltrans).

"We did see some evidence of damage on the surface," Caltrans' chief bridge engineer Brian Maroney said at a news conference. Maroney had ordered the testing.

Bay Bridge anchor rods
Caltrans

Caltrans discovered water at the bottom of the tower where 424 rods anchor the span to its base. The 25-foot rods are protected by metal sleeves filled with grout and covered with caulk caps that are supposed to keep them dry.

However, even if the rods that remain in place are cracked and show signs of corrosion, Maroney said it was "not a safety issue" and would result only in extra damage to the tower if they were to fail in an earthquake, the San Francisco Chronicle reported.

Sitting in Water

The single-tower, self-anchored suspension bridge features a unique design in which the 137-strand main cable loops over the tower and under the bridge, where the strands are inserted into sockets that are attached to thread rods. The rods pass through the walls of two chambers on the bridge's east end, where they are locked in place.

There are 152 six-inch solid steel dowels underneath the bridge's deck that keep the 525-foot-tall steel tower from slipping off its foundation. There are also 424 25-foot-long steel anchor rods that provide seismic stability for the foundation and tower in the event of an earthquake.

To prevent contact with water, all 424 anchor rods are surrounded by long steel tubes, which were supposed to be filled with grout.

"Unfortunately, the state's contractor failed to properly fill all the 424 tubes with grout," Caltrans said.

In September 2014, inspectors discovered water at the base of the SAS tower beneath caulking around the rods. When the problem was discovered, Caltrans reported that water had been found on 95 percent of the rods, standing an inch or two deep between the grout and the caulk caps.

Several tubes were missing "inches to meters" of grout; seven had no grout; and 17 were sitting in gallons of water because they were not properly filled with grout, Caltrans said.

Ongoing Fixes, Testing

The contractor, joint venture American Bridge/Fluor Enterprises, took responsibility and agreed to work with Caltrans to fix the problem, the agency said. Since then, contractors have drilled inspection holes in the existing grout to investigate anchor rod conditions.

One of the rods was removed and subjected last year to extensive laboratory testing that included soaking it in salt water for extended periods and then stressing it to failure. The purpose of the testing was to determine whether and to what extent the rod's protective galvanizing had been compromised, Caltrans explained.

It took nearly a month and the help of hydraulic torque wrenches and 100-ton jacks to remove the anchor rod for testing.

Bay Bridge
Tom Paiva / BATA via BayBridgeInfo.org

The $6.4 billion San Francisco-Oakland Bay Bridge opened to traffic Sept. 2, 2013.

A preliminary test showed that galvanizing was missing around the threads at the bottom of the rod, "leading to potential corrosion of the steel of this one bolt," Caltrans said. Additionally, scanning electron microscopes at 1,000-times magnification showed a microscopic crack in the rod material.

More Testing Ordered

However, Caltrans said it was too early to draw conclusions about the cause or significance of the cracks.

"We have one preliminary test result that shows a microscopic indication on the surface of the steel of one bolt," said Maroney.

"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," Maroney said.

History of Rod Issues

Anchor rods have posed multiple problems for Caltrans. Another set of rods, designed to connect two columns that rise from the underwater foundation to the concrete pier cap, broke just days after crews tightened them in place in March 2013.

Originally installed in 2008, the holes surrounding the anchor rods had been left to fill with rainwater for five years before being tightened.

This video from Caltrans shows how the department is checking the grout surrounding the anchor rods.

Caltrans later released hundreds of pages of documents that showed its inspectors had found structural integrity issues with some of the bolts years before. State engineers had also ordered extra tests on the bolts in 2008, but those tests were not done after the contractor disputed whether they were required.

That set of rods is no longer placed in service, and 2,000 other rods that were fabricated separately have not failed or showed hydrogen embrittlement, according to Caltrans.

Caltrans revealed in October that an inspector had performed a video inspection on the rods in August 2011 and found signs of corrosion. At the same time, the inspector visually examined the rods' sleeve holes and found standing water plus "objects such as cigarette butts, U-bolts and wood chips."

Leaks, Cable Corrosion

Several other, unexpected issues have also marred the engineering marvel.

In February 2014, a routine maintenance inspection discovered hundreds of leaks in a supposedly watertight steel chamber that supports the bridge's suspension span. Rain water dripped onto the road deck and, although the amount was said to be minimal, Caltrans had no idea where it was coming from.

An investigation by The Sacramento Bee in April 2014 found signs of corrosion on cable sections. Some strands showed rust and "crack-like indentations" where they join the sockets, as well as "white and red-brown rust ... in patches" on several of the rods' threads.

Caltrans said the issue was part of routine, ongoing work and the rust was attributable to "metal shavings/particles generated by grinding and other work."

Officials on the bridge project released an itemized list of potential defects and flaws in May 2014, showing that maintenance work could potentially add millions to the project's total.

   

Tagged categories: Bridges; Corrosion; Department of Transportation (DOT); North America; Program/Project Management; Testing + Evaluation

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