This SF Chronicle article describes the work, and has some great pictures:
Crews carefully lifted and then lowered the 105.6-foot-long, 500-ton tower leg into place about 6:30 p.m. and began bolting it to the third level. All told, it takes about 30 hours to install each leg.
When all four are bolted in place, by Friday, if weather cooperates, the tower will stand at 480 feet of its ultimate 525 feet.
The weather has indeed cooperated, and the fourth-segment work has indeed finished as planned: Major Milestone Reached in Bay Bridge Construction proclaims the local ABC news station, with some nice video of the tower's construction.
At the end of the ABC video, you can see some pictures of "the saddle", which is the last piece of the tower. The saddle sits on top of the tower and the suspension cables rest in the saddle.
Over the next two months, two major events are soon to follow:
- The saddle is to be raised and mounted atop the tower, completing the main tower construction.
- The eastbound connection of the old bridge will be re-routed somewhat, so that the construction crews can start attaching the new bridge to the Oakland waterfront.
Up to this time, the new bridge has been standing disconnected, neither end joined to its final destination. Connecting the new bridge to the waterfront will be a big event. I suspect that Caltrans will probably schedule the big re-route operation over the long Memorial Day weekend, as it will be quite disruptive.
It's an astounding construction project. Engineers involved in the project seriously discuss topics such as the proposed 150-year lifetime of the bridge. Can they achieve this? Well, I won't be around to know, but if they do, that would be quite impressive, as the current bridge has lasted 75 years so far.