What Happened To The Bay Bridge?

farnsworth writes: Tony Alfrey has put together a fascinating page with some history, analysis, and possible explanations for what ultimately went wrong with the recent emergency repair of the San Francisco-Oakland Bay Bridge. The bridge has been closed for days and is not scheduled to open for days to come, hugely inconveniencing more than 250,000 people a day. His analysis touches in possibly poor welding, possibly a fatally flawed kludge, and a the absence of a long-term fix or adequate follow-up by Caltrans, who are responsible for the bridge. This is a great engineering community, what other info do you have?