A wobbly bridge - part 3

On Wednesday, Tony Kennedy and Paul McEnroe of the Minneapolis Star Tribune reported on the stories of two structural engineers who spoke on condition that their names not be revealed. They pointed to three joints on the southeast side of the bridge just north of the lock. The Star Tribune reports,

All three joints appear to have been damaged by some primary force -- not from secondary impacts sustained during the collapse, the engineers said.

The first one is called L9, so called presumably since it is the ninth joint on the lower side of the structure, starting from the south side. The second joint answers to the name of L11. It's two joints further north. In between, up above, right below the road, there's the third joint, U10. Together these three witnesses, clothed with their gusset plates, one in red, formed an arrow pointing up. What were they pointing at? Were they pointing at the mobile concrete mixer as they fell?

Compare the photos (here and here) of where the mixer landed and the diagram of the three joints. Note the location of the lock.

Here are the 3 joints in the center of a photo.

For more on the question of the mobile concrete mixer and whether it had been mixing concrete on the bridge, read part 2.

Kennedy and McEnroe go on to report that one of the two engineers said that bearings retrieved from the river "appear to be lacking marks of wear." Rollernest bearings sat on top of the piers and were designed to allow the bridge to expand and contract with changes in temperature. The bridge was to roll over the bearings back and forth with the seasons. If the bearings had been stuck, as this report would indicate, then the bridge itself would have been bent out of shape, in a state of undesirable tension, joints weak from past contortions.

At the very moment the bridge snapped, I was running around Lake of the Isles, keeping my run short since it was a hot evening.

Could it be that the bridge was cocked in the heat, poised for a catastrophe sparked by the quivering of concrete in the mobile mixer? Some bridges are just too old for such excitement.

• A wobbly bridge - part 1
• A wobbly bridge - part 2
• A wobbly bridge - part 4
• A wobbly bridge - part 5
• A wobbly bridge - part 6

Credits:
Mordac (photo #1, northwest side of bridge)
ebrandt78 (photo #2)

Update (Nov 16, 2008, 9:00 pm Central): According to the NTSB report, the rollernest bearings appeared to have been functioning properly.

Bridge Description and Collapse
by Jim Wildey

A wobbly bridge - part 2

On August 26 I sat on a gentle hill, amongst a group teeming with artists and Scrabble players, listening to Davina and the Vagabonds at the Lake Harriet Band Shell. It was there that I heard a story about the bridge. I don't know if it's true. I only know that I was told this story.

I relay it to you now as a question mark, a big, hairy question mark, regarding events that may or may not have happened 3 days, 2 days, one day before its collapse. This is an unconfirmed report. Let me repeat that. This is an unconfirmed report. I was told yesterday that MNDOT has asked its employees not to talk. Too bad, I was already going to blog about it. This collapse hit too close to home. It's my business and yours, too, if you live around here, as citizens, as residents. This was a government project, and I don't believe national security is at stake. So it demands transparency.

It may turn out to be false. It may turn out to be true. It may turn out to be somewhere in between. If it turns out to be on the truer side, then as a citizen I would then encourage the state government to find a different contractor next time.

There are four degrees of separation between me and the events, or so I am told by my deep throat. She is friends with someone who works with the partner of a MNDOT employee.

Here is the story she told.

Day minus 3 or so
Two days before the collapse, the MNDOT employee took a day off. Before she took that day off—it sounded like it was the day right before that— she had argued with the crew telling them not to mix the concrete on the bridge. Apparently this is standard practice on bridges, that you not mix the concrete on the bridge. You can mix it off the bridge. You can pour it on the bridge. You just can't mix it on the bridge.

Day minus 2
What did they do on her day off? Apparently they mixed the concrete on the bridge. So I have been told. The question is: Did they really do this? Did they really do this despite being told not to by MNDOT?

Day minus 1
The MNDOT employee returns to work and returns to the bridge. When she finds out that they went ahead and mixed the concrete on the bridge, she's upset. The retort? According to the story, someone on the crew said something like this, "See, we mixed it on the bridge, and nothing happened."

One of the 7 men she talked with would not survive the next day.

Here is where the story ends.

Day zero
Progressive Contractors, Inc., is reported to have been "preparing to pour two inches of concrete when the span gave way." In photos of the collapsed bridge, a concrete mobile mixer is there amid the rubble.


It's the truck with the white cabin.

Were they following protocol? Were they mixing concrete on the bridge after being told not to? That's the question.

There are dangers in playing telephone, yes, but the real danger lies in opaque government.

• A wobbly bridge - part 1
• A wobbly bridge - part 3
• A wobbly bridge - part 4
• A wobbly bridge - part 5
• A wobbly bridge - part 6

Credits:
Tony Webster (photo with concrete mobile mixer)

Postscript: Oh, and the bridge hadn't been wobbling after all (see part 1). My mistake. Always best to upsub antefiling.

Update (Oct 8, 2007): Another mistake of mine. Now MNDOT says, reportedly, that they won't release inspection reports on our local bridges out of a concern for "national security." So I was wrong when I said national security was not at stake.

What has happened to the open society and to government transparency? When does 911 become an excuse?

Update (Dec 20, 2007): The Minnesota legislature is hiring a special counsel to investigate MNDOT and the bridge collapse, according to Pat Doyle and Mike Kaszuba in the Star Tribune today.

Update (Jul 31, 2008): Yesterday I came across evidence that concrete mixing was indeed taking place on the bridge. See A wobbly bridge - part 4.

Update (Jul 31, 2012): There were actually only 3 degrees of separation my source told me later.  She had spoken directly with the partner of the MNDOT employee.

A wobbly bridge - part 1

On the surface, Minneapolis's 35W bridge over the Mississippi River was a simple road. Driving along it, you'd think it was on the ground. It had no cables, no towers, no art. I rarely noticed the view. The exit lane for Hiawatha demanded too much attention with all the merging going on. There was only the road, a gray familiar path.

Its art lay below, in its airy perch. The deck floated 115 feet above the water. It's remarkable how people survived the fall.

It had a plain top. There's the sign for my exit lane.



On Tuesday I came across a man looking at the ghost-town traffic still caught on the north side. He had driven over the bridge not a day before its collapse. He turned to me and told me how it had wobbled, even then.


The Minneapolis Star Tribune reported Monday,

Some workers said that the bridge had been wobbling unusually in the days before the collapse, according to Minneapolis police Sgt. Tim Hoeppner. With every layer of concrete that they removed, the bridge would wobble even more, they told him.

When a bridge starts wobbling, best not to ignore it.

• A wobbly bridge - part 2
• A wobbly bridge - part 3
• A wobbly bridge - part 4
• A wobbly bridge - part 5
• A wobbly bridge - part 6

Credits:
TimDan2 (photo #1)
Mordac (photo #2)
kj415 (photo #4, derivatives allowed, cropped by me)
puppethead (photos #3, #5-7
ibran (photo #8)

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