Bay Bridge rod troubles extend to base
Jaxon Van Derbeken | San Francisco Chronicle
Updated 8:56 pm, Saturday, May 11, 2013
The base of the new Bay Bridge eastern span's signature tower is secured by more than 400 high-strength steel rods that were galvanized under conditions Caltrans barred as putting them at risk of cracking, The Chronicle has learned.The tower is the dominant feature of the $6.4 billion eastern span, which is supposed to open over Labor Day weekend - a schedule that is now up in the air because of problems with how the tower rods and nearly 2,000 other steel fasteners were made.
The 525-foot-tall tower has been the central feature of the span since plans were drawn up in 1998. The landmark survived then-Gov. Arnold Schwarzenegger's efforts in 2004 to scrap it due to cost and replace it with a concrete causeway. In recent weeks the scaffolding has gradually disappeared from around the tower, revealing the structure silhouetted on the Golden State Warriors' uniforms.
Not visible are the 424 threaded rods - 24 feet long and 3 and 4 inches in diameter - that are among those Caltrans has belatedly realized are vulnerable to being invaded by hydrogen that could cause them to become brittle and crack.
Caltrans can sample many of the 2,306 problematic steel rods on the span in an effort to determine whether they will hold up. However, it cannot easily inspect, remove or replace those that sit at the base of the tower because the mammoth structure was lowered onto them in pieces.
"We are aware of the issue," Caltrans spokesman Will Shuck said of the tower rods. "These are going to get added scrutiny. We're going to make 100 percent sure they are safe."
In an earthquake, the rods would perform a vital task - countering the swaying forces on the tower. Caltrans officials say the rods are not being subjected to a high stress load, which they say reduces the risk they could crack.
Some outside experts, however, said the way the tower rods were manufactured makes them vulnerable to minor cracking that could suddenly worsen in an earthquake.
Problems in long run
"The problem is going to be that, over a long time, you start to see some cracks," said Russell Kane, an expert on metal embrittlement and corrosion who owns a consulting firm in Texas. In an earthquake, he said, "you are going to have some of those pre-existing cracks that are going to grow like crazy."
"If you have cracks in them, all bets are off," Kane said. "The thing could be swaying in the wind very quickly."
Like the other problematic steel rods on the eastern span, the ones at the base of the tower were made to an industry standard known as A354 BD. That denotes that the steel is of high strength and is allowed to be galvanized - a process in which the rods are dipped in molten zinc, intended to keep them from rusting.
But federal and state highway officials have long warned against galvanizing such high-strength steel and using it on bridges because of the possibility it will fail.
Galvanizing risk
Galvanizing can seal in hydrogen, which can cause cracking. It can also make it easier for hydrogen to invade the steel through flaws in the coating, by way of an electro-chemical reaction.
Caltrans banned such rods from bridges in 2000 because of the chance the steel could become brittle during the galvanizing process. The agency made an exception, however, for the A354 BD galvanized rods on the new Bay Bridge - after instructing manufacturers to remove a step in the galvanization process in which the metal is pickled in hydrochloric acid before being dipped in zinc. They hoped that would minimize the risk of hydrogen invasion.
"Generic specifications are for a run-of-the-mill bridge," Caltrans Director Malcolm Dougherty explained, "and this bridge is not run-of-the-mill."
In avoiding the acid baths, Caltrans was following the advice of the American Society for Testing and Materials, an industry standards group that establishes specifications.
Source: http://www.sfgate.com/bayarea/article/Bay-Bridge-rod-troubles-extend-to-base-4508623.php
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