“The Famous Bay Bridge Crack”

8 thoughts on ““The Famous Bay Bridge Crack””

1. Jared says:

   October 31st, 2009 at 6:38 am

   He makes a lot of references to the fix being under designed and the engineer that created it not doing having a lot of time for analysis, but offers none of his own or any evidence (or even rough calculations) to indicate that it was under designed. I love the pics and info on the story but would prefer some more objective analysis or at least something besides his gut to back up his ideas, I can guarantee you that the engineer who designed it used a lot more than his gut to determine if it would hold the load.

2. Anonymous says:

   October 31st, 2009 at 7:16 am

   If a weld failed, it’s the welder’s fault. In a properly welded piece, the join is the strongest part.

3. gear head says:

   October 31st, 2009 at 10:36 am

   if the repair only lasted a month an a half then I think it’s pretty safe to say that it was an ‘under designed’ repair solution. The only thing that voids that statement is the evidence of new forces or causal factors that were not present when the linkage failed originally. I have no idea what kind of dynamic loads those linkages are working to but I find it interesting that only one linkage of 4 actually cracked. Looking at the corrosion and surmising that the linkage is probably seized would be my uneducated guess.

4. Dustbuster7000 says:

   November 2nd, 2009 at 12:01 pm

   The webpage is interesting, but the recent update at the top linking to the Channel 4 site is interesting. The T-bars and the saddle the piece described in the sci-experiments website, and from Caltrans explanation, the T-bar was only tack-welded to the saddle. These welds are only there to hold the t-bar in place during assembly. Once the tie-rods are tensioned, even loading of the tie-rods keeps everything in place. When one of the tie-rods failed, the sudden change in the load on the saddle and t-bars caused the tack welds to fail, separating the two and allowing the t-bar to fall onto the bridge.

   The new arrangement probably uses full seam weld (the Caltrans guy talks about a ‘structural weld’), effectively making the saddle and t-bar one piece. The strength of this weld is very much larger than that of the tack-welds, but takes significantly longer to perform.

   Whats more important is why the tie-rod failed and the changes to the design imply that the rods failed by fatigue induced by wind (and other) vibration, possibly in combination with corrosion damage (although the time from Labor Day to end of Oct makes it less likely that corrosion was a major factor). The failure was probably in the area of the tie-rod nut, since the radiused nut shown would help reduce the stresses on the tie-rod at the point where the nut contacts the t-bar.

   The position of the saddle also allows Caltrans to patch or reinforce the original crack if necessary, but added welding heat to the area might be judged more likely to worsen the crack and thus be avoided.

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