Wednesday, May 15, 2013

New Bay Bridge....A Disaster....

New California Bay Bridge is a mess.

California spent 6.4 Billion Dollars on a brand new Bay Bridge to ensure safety in an Earth Quake.
It is the largest public works project in the States history. They outsourced part of the bridge to be made in China and that work came back all screwed up. The steel had cracks, and the welds were poor.

Now they find even more issues with the bridges steel bolts and rods. The bridge was suppose to open in Sept but now might not open for a long time.

If you want to know how to waste tons of money, not create US jobs, and end up with a terrible end result…… this would be a good case study.

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.

In an earthquake, the rods would perform a vital task - countering the swaying forces on the tower.
the way the tower rods were manufactured makes them vulnerable to minor cracking that could suddenly worsen in an earthquake.
"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 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.

In March, 32 of the rods on a seismic-stability structure on the new eastern span snapped when they were tightened, even though they had not been subjected to hydrochloric acid.

No comments:

Post a Comment