Guessing the contractors tried to save some money and got some high-quality Asian steel for a lower price.
Oh that was in the design from day one.
“American steelworker unions have disparaged the Bay Bridge contract by accusing the state of California of sending good jobs overseas and settling for what they deride as poor-quality Chinese steel. Industry groups in the United States and other countries have raised questions about the safety and quality of Chinese workmanship on such projects.”
http://www.nytimes.com/2011/06/26/business/global/26bridge.html?pagewanted=all&_r=0