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The 1%: 2 Bridge Rods Fail Pull Tests

Friday, May 29, 2015

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OAKLAND, CA—Two of the steel rods used for seismic stability on the San Francisco-Oakland Bay Bridge have failed testing that simulates a strong earthquake, California transportation officials say.

However, 99 percent of the tested anchor rods can withstand a major earthquake, an optimistic California Department of Transportation said Wednesday (May 27).

The group of rods—424 in all—are meant to limit damage during a quake by preventing the structure's 525-foot-tall tower from rising off its foundation.

"These anchor rods are just one of many seismic innovations on this bridge that help ensure resiliency of the structure for decades to come," Brian Maroney, chief engineer on the $6.4 billion Bay Bridge project, said in a statement.

Testing Results

Caltrans has spent the last several weeks performing pull testing on 408 of the 25-foot-long anchor rods after reporting in October that it had discovered some of the rods in the tower foundation were exposed to water.

anchor rod testing
Images: Screen grabs via Caltrans News Flash #26 video

After testing 408 of the 424 steel anchor rods designed to hold the San Francisco-Oakland Bay Bridge in place during a large earthquake, Caltrans announced that two of the rods failed testing.

The pull test involves a powerful jacking device that grabs and yanks the rods with "enormous force" to verify integrity, the agency explained.

Of the 424 rods, Caltrans reported that:

  • 408 were tested;
  • 406 passed the test;
  • 14 could not be tested because the threads did not stick out far enough to connect to the testing machine; and
  • 2 were removed for laboratory analysis.

"The two rods that did not pass the test will be sent to a laboratory to determine exactly what happened to them," Maroney said.

Another round of testing will help determine how long the bolts will remain sound after long-term corrosion exposure in a laboratory.

The specific testing protocol is under development and will be reviewed by external experts and the Toll Bridge Program Oversight Committee (TBPOC), according to Caltrans.

The TBPOC, which has managed the bridge since 2005, is comprised of representatives from Caltrans, the California Transportation Committee, and the Bay Area Toll Authority.

Water Blame Game

The rods are protected by metal sleeves filled with grout and covered with caulk caps that are supposed to keep them dry.

The state's contractor, American Bridge/Fluor, claimed responsibility for not properly filling the anchor rods' metal sleeves with grout and started working on a solution to the problem.

An inital round of testing revealed tiny cracks on one of the rods and showed that galvanizing was missing around the threads at the bottom of the rod.

Ongoing attempts to remove water seeping into the sleeves and other locations have been mostly unsuccessful, touching off an exchange of blame between Caltrans and American Bridge/Fluor.

'Popping' Noise

One of the broken rods was removed May 19 during a round of testing. Caltrans said the rod was six inches shorter and "visually different" than the others. Once removed, the bolt was found to be broken near its bottom.

San Francisco-Oakland Bay Bridge

Since opening, the bridge has faced a leaking steel chamber said to be watertight, shifting rods near the massive suspension cable, corrosion and "crack-like" indentations on cable strands, and other issues.

The second rod that failed was of normal length but failed to hold a load when it was pulled, Caltrans spokesperson Leah Robinson-Leach told The San Francisco Chronicle.

Caltrans official Dan McElhinney told The Chronicle the failure could have been caused by stripped threads, corrosion from sitting in water, or both.

"Two sources close to the bridge project" told the newspaper that the rod made a popping noise, suggesting a crack.

"We won't know the cause until the rod is removed and provided for laboratory testing," Robinson-Leach said.

Robinson-Leach said initial results could be available in one to two weeks, but final results could require more tests and take months.

According to Caltrans, a preliminary engineering analysis showed that even if all of the rods were compromised, there would be no safety issue during everyday use or during or after an earthquake.

Engineers involved in the Bay Bridge project have traveled the state to meet with universities, public and private sector engineers, metallurgists, experts and critics, Caltrans said. Hundreds of thousands of records, including fact sheets, construction documents, photos and videos, are available online.

Another Anchor Issue

Caltrans started investigating the condition of another set of rods in 2013 after 32 of them were damaged when they popped loose just days after workers started tightening them. Over 2,000 of the rods, which range from nine to 24 feet in length, are installed in the bridge.

A few weeks after the rods broke, Caltrans released hundreds of pages of documents that showed its inspectors found structural integrity issues with some of the bolts years ago.

The rods were originally installed in 2008, when they were installed into holes in the concrete caps. These holes filled with rainwater and were left like that for years.

Caltrans had ordered tests on the bolts in 2008, but those tests were never done after American Bridge/Fluor disputed whether they were required.

Caltrans anchor rods

Caltrans has spent the last several weeks performing pull testing on 408 of the 25-foot-long anchor rods after an October 2014 report from the agency said it had discovered some of the rods in the tower foundation were exposed to water.

Since the bolts could not be removed, the agency furnished a steel saddle retrofit, which allowed the state to open the bridge as scheduled Sept. 2, 2013.

In October 2014, Caltrans revealed 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."

Plagued with Problems

The anchor rods aren't the only issue with the structure. Numerous other issues have popped since the bridge opened.

In February 2014, a routine maintenance inspection revealed that rain water was dripping onto the road beneath a supposedly watertight steel chamber that supports the suspension span.

Then, in April 2014, The Sacramento Bee reported that several of the rods' threads had patches of white and red-brown rust and some of the strands showed rust and "crack-like indentations" where they join the sockets.

While inspecting rods for potential cracking risk in May 2014, Caltrans discovered that rods anchoring the massive suspension cable had shifted since installation and were too close to sharp plates inside the bridge. Repairs were required due to concerns that a strong earthquake could cause the rods to vibrate into the sharp steel edges, potentially damaging the main cable.

Less than a year after the bridge opened, bridge officials said it had to be repainted after thousands of steel particles from grinding work became embedded in the paint, causing rust stains.

   

Tagged categories: Bridges; Corrosion; Department of Transportation (DOT); Laboratory testing; North America; Program/Project Management

Comment from Stephen Dobrosielski, (5/29/2015, 8:21 AM)

"According to Caltrans, a preliminary engineering analysis showed that even if all the rods were compromised there would be no safety issue during everyday use or during or after an earthquake" .... if this is truly the case, why are the rods installed? I will be in the Bay Area in late June and I can't wait to view this structural edifice firsthand. I sincerely doubt that the bridge can hold the weight of all the studies, analyses, and reports ... during everyday operations or during or after an earthquake.


Comment from M. Halliwell, (5/29/2015, 10:50 AM)

The rods are likely there to keep the bridge in place. There's a difference between being able to structurally carry a load (the concrete can do that by itself as it can carry the compressive load) and resisting the movement from an earthquake (i.e. surfaces pulling away...something that needs a tension member like steel rods as concrete is quite weak under tension). I understand what the engineers are saying, but it also sounds like this bridge is a test bed for some new ideas and is having a lot of growing pains as a result.


Comment from Fred Wittenberg, (5/30/2015, 10:04 PM)

With the problems stated 2 pictures up, one would think that this bridge was designed & built by novices. Yet, this is in California, where due to seismic activities in the past and possible future events, you'd expect them to be at the cutting edge. I've driven across it, and as an engineer, I have a lack of confidence in it. Doctors hide their mistakes with flowers. Architects hide theirs with ivy. But an engineer's mistakes are living momentous to their stupidity.


Comment from Tom Schwerdt, (6/1/2015, 8:42 AM)

Stephen: Large modern structures usually have significant redundancy. One recent cable stay bridge I visited had enough redundancy that you could remove any 2 cables and still carry the full load. If 2 cables are ever damaged, the bridge will still stay up.


Comment from Stephen Dobrosielski, (6/2/2015, 7:29 AM)

Lot of good points in this discussion. If the rods are intended to hold the tower down on the foundation during an earthquake event, then their tensile strength is utilized as a clamp to develop friction between the tower and the concrete. I always was of the opinion that earthquake design involved resistance of lateral movement, but I could be wrong in that thought. As to redundancy, that word was on the tip of my tongue when I first posted. Is the fact that a cable stayed structure can still function with two adjacent stays removed by design? or is it simply the applied loading being redistributed in a different load path versus the original design. Again, I don't know the correct answer, but am willing to consider opposing thoughts.


Comment from Tom Schwerdt, (6/4/2015, 8:56 AM)

Stephen - on the cable stay, I believe it was a design requirement.


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