New Bay Bridge—What's Up With The Bolts? Fail...

I have been poking around a little with a sharp stick amongst the many top-notch journalistic articles about this disaster, and present what I have learned. Sadly, this story is only halfway finished.

The New Eastern span of the Bay Bridge is finally finished. Yes, it has been like a Keystone Cops comedy, but not in the humorous sense. There are many problems, but today's focus will be the anchor rods that snapped off when tightened. These connect the bridge deck to the concrete support columns sunk into the bottom of the Bay.

A BIT OF HISTORY

I am old enough to remember the genesis of the new eastern span. The year is 1989: the 3^rd game of the World Series (that year, it was the Bay Bridge Series: SF Giants and Oakland A's) is about to start, and I am rushing home from work to catch the first pitch. Before I can get home for a quick shower, the Loma Prieta Earthquake strikes. All TV and radio stations are knocked off of the air, and the game was canceled. The trestle portion of the eastern span failed, and it took a month to repair and reopen.

By 1997 (yes, it really took that long and the costs in the meantime increased), there was a decision to be made: retrofit ($1.5b and 5 years) or replace ($1.7b and 7 years)? The latter was chosen. In the end, the cost was $6 billion, and would take a decade to finish and open for traffic.

WITH VISIONS OF STEEL BOLTS DANCING IN HER HEAD

Many casually refer to the failed pieces as “bolts”. Technically speaking, they are connecting rods (picture here). Bolts have an integral head, is inserted through a hole, and is tightened with a nut on the other end. A connecting rod does not have a head, but is tightened with bolts from either end. This is a contributing factor to the failed rods.

'THOU SHALT NOT GALVANIZE'

When hardened steel is galvanized and used in a bolt, the material spec is called A490. When the same steel is used in a connecting rod, it is called A354BD. The former is strictly forbidden for use in bridge construction. The latter spec stops just short of outright ban, and therein lies the problem. Even still, A354BD is prohibited by standard bridge building practice, and Caltrans' own regulations bans its use. The design engineers for the bridge think they have a workaround, so specified A354BD connecting rods. In ordinary words, they cheated.

The reason they are banned, is that they are brittle and can snap when tightened, and have a tendency to crack over time when placed under load, as they are in the Bay Bridge. When the A354BD rods were tightened under load, some of them snapped.

2008 vs. 2010

When I hear people talk about these problems, there are often remarks about inferior quality Chinese steel. The rods in question where manufactured in Ohio.

These were made in 2 batches, one in 2008 and another in 2010. The rods that failed were from the 2008 batch. Despite the fact that the engineers fudged the specification, the 2010 batch seems to be OK.

BAY BRIDGE, THE NEXT GENERATION

Some of these things can be replaced, others are inaccessible since they are embedded in concrete. They ended up doing a retrofit, by attaching doo-hickeys to the rods in question to restore their strength. A permanent solution is still needed.

I did not read any firm, engineering opinions about the eventual fate of the A354BD rods. The best I saw were a couple of off-the-cuff remarks that they should be OK in an earthquake. As a taxpayer who helped pay for this disaster and someone who occasionally crosses said bridge, that is not very reassuring.

RUST?

You may have heard more recent stories about rust. This is a totally different, and much more dangerous problem. The bridge uses steel cables, called tendons, throughout. Protected from the salt spray from the Pacific Ocean, they give the bridge strength and seismic safety and are part of the so-called self-anchoring concept. Some have noticed orange rust at the connection points for the tendons. Problem is, rust tends to cause the tendons to snap off during, for example, an earthquake. If enough of these fail, it will cause partial if not total failure (collapse) of the bridge. Caltrans has responded by saying that only a tiny % are corroded, and this does not pose a structural danger. For the sake of those who are crossing the bridge during the next big earthquake on the San Andreas Fault, let us pray that they are correct.

150 YEARS

This is the projected lifespan of the new eastern span. Well, perhaps. In light of the problems (and there are yet others: flexing deck plates, poorly fabricated concrete pylons), I am doubtful. Perhaps they should start work on the a new bridge right now.