Still chasing the "scour" ghost, eh? I thought we put that theory to rest shortly after the failure... :-(
IM(NS)HO, the tilt of Pier 6 was what we in failure analysis call a "verified ugly" -- an obvious artifact that distracts those who are prone to jump to conclusions from the real point and cause of failure. Again, IM(NS)HO, Jeffers has it "nailed".
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In the period immediately after the collapse, I did extensive, frame-by-frame time-lapse analysis of the security cam video taken of the pier 6 end of the bridge -- looking across the river from the locks area at the pier 6 end of the main span. And, IIRC, I copied you on those findings...
Although the splash/spray (after the main span hit the water, of course) obscured much of the pier itself, I detected no riverward shift of the top of pier 6 until after the mainspan had collapsed, and after the splash had subsided and after failure of the side spans on the pier 6 side was well underway.
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In failure analysis, "gut instinct" can lead you into never-never land. Try presenting "gut instinct" as your data some time at the Reliability Physics Symposium -- but put your earplugs in first... '-)
I’m not a structural engineer.
But why did Pier 6 move at all? It is not only a tilt, but a dislocation. If it was anchored properly, it should not have moved the way it did, but rather collapsed in some way. The center span collapsing most likely would have separated at the expansion joint at the approach span, at both ends.
The longer part of the collapsed center section started from Pier 6. The shorter section of the span came from Pier 7. Pier 6 has its rocker bearings and plates intact atop the pier. Pier 7 has the piertops shorn off where the bearing plates were.
The longer section of the bridge fell pretty much in line vertically. The shorter section is off to one side of Pier 7 by a fair degree.
What does that indicate? To me it indicated the presence of a tremendous horizontal force,possibility building over time, not just a failure where gravity then took over.
Could the bridge after failing at U10 pushed toward Pier 7 as it collapsed? Sure it could.
And the moment force at Pier 6 could have been sufficient to dislodge the entire pier structure? Possibly.
The bridge was inspected for scour. But the visibility by Pier 6 was always almost zero due to turbidity caused by the extreme current of the river. Even post collapse recovery efforts were hampered by the extremely low visibility in the water.
I am having trouble with the article’s explanation that the gusset plates were supposed to be twice the thickness. The bridge should have collapsed as soon as the number of lanes was doubled from four to eight years agoif that was the case.
The bridge was designed in the 1960s when design was very conservative, so adequate safety factors should have been involved.
Jeffers submits that U10 failed due to corrosion—that would make more sense than this article.
But until the subsurface condition of Pier 6 is investigated, I cannot rule out the possibility of its role.
That’s just my opinion. Sometimes Occam’s Razor is right and sometimes it is not.
>In failure analysis, “gut instinct” can lead you into never-never land. Try presenting “gut instinct” as your data some time at the Reliability Physics Symposium — but put your earplugs in first... ‘-)<
‘-{