Did they give any idea as to the cause?

Was there a collision with the pier or large temperature change?

Since I don't work for the agency that maintains and inspects it, all I could do is spread rumors and speculation.

I will say that there was no collision with the pier, and I don't think thermal effects can account for all of it.

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      "Come to think of it, there are already a million monkeys typing on a million typewriters, and the Usenet is NOTHING like Shakespeare.

       - Blair Houghton

The following is an excerpt from the August 3, 2005 edition of the Albany Times Union (www.timesunion.com).

" "A routine bridge inspection nearly two years ago found serious problems with the bearings supporting a section of elevated highway that ruptured and dropped 2 feet last week.

Yet, state transportation officials said they made no plans to fix the problems with the Empire State Plaza ramp before the next planned inspection this fall.

The overall rating on the 24-section ramp that links Interstate 787 northbound with the plaza was set at 5, or generally "good," on a scale of 1 to 7 in the November 2003 inspection report. A set of bearings atop the concrete pier where the break occurred, however, received a rating of just 2.

"You can't look at that out of context," said acting state Transportation Commissioner Thomas Madison on Tuesday, six days after the ramp came apart and forced major detours affecting thousands of motorists. "You have to look at the bridge as a complete system."

DOT's rating system for individual bridge parts describes 2 as a grade used to shade between 1, defined as "totally deteriorated, or in failed condition," and 3, defined as "serious deterioration, or not functioning as originally designed."

"This was not a condition at the last inspection report that caused enough concern to have any immediate action taken," Madison said during a technical briefing for reporters, where the inspection report was released late Tuesday afternoon.

Nonetheless, one of DOT's top engineers said it's now clear that the poorly rated rocker bearings, steel supports designed to accommodate weather-related expansions and contractions of bridge sections, could have been a factor.

"There were some low-rated bearing elements that may have had something to do with this," said George Christian, the chief structural engineer for the state Department of Transportation.

The set of poorly rated bearings was on the section of the ramp that remained atop the pier, sliding toward the section that tumbled from its bearings and nearly fell off. The group of bearings was rated so poorly because they were tipped at an unusually extreme angle, Christian said.

"It was tilted, definitely, more than we would have expected it to be tilted for the conditions at the time of the inspection," he said." "

Without necessarily getting into the specifics of this case, what would make a bridge move over so far?

Hg

Eng-Tips guidelines:  FAQ731-376

HgTx - Cummulative thermal expansion (or contraction) - sometimes the hardware goes haywire and only works in one direction.

The only example that I participated in first hand did not involve a bridge, but was a mile or so of welded rail that butted up to a rotary railcar coal unloader. Every summer, for 10 year or so, the maintenance staff had to remove 6 inches or more rail as it started proturding into the unloader. In this case, investigation revealed that the track could "grow" properly on the hot days; but the only way it could "shink" was by slowly straightning out a curve in the track a quarter mile away. The track, ties & all, had been visibly moved toward the edge of the ballast.

www.SlideRuleEra.net

In a few shots, it looks like the pier is out of plumb.

It's near a river bank, with a lot of clays and glacial detritus. Perhaps there is a problem with the piles leading to differential settlement.

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      "Come to think of it, there are already a million monkeys typing on a million typewriters, and the Usenet is NOTHING like Shakespeare.

       - Blair Houghton

I've inspected several hundred bridges; quite a few with rocker bearings. It's not uncommon to find rockers that were set improperly (vertical at 68 degrees F) or to find rockers become out of plumb due to rust or a build-up of debris.

It's been rather hot in the northeast recently. So, if the rockers were significantly out of plumb a hot day could literally push them over. Also, note that one span is curved; from the photos, it seems to me that this is the one that collapsed. Curved bridges as well as straight bridges with large skews are subjected to abnormal movements. The problem is compounded if the bearings aren’t set perpendicular to the direction of movement rather than perpendicular to the girder. This could have been a contributing factor.

 Unfortunately, the news report and the photos aren’t presenting a clear picture. As Lt. Columbo would say, “something’s bothering me.” In the first photo, the left span is the one that collapsed but the rocker for the fascia girder has its base pointed to the right and then there’s another rocker that’s standing (look between the joint of the two girders).  If the bearings at the left side were expansion rockers, the bearing for the fascia girder should in all likelihood have been pointing to the left.

I’m trying to get some information from colleagues in the area.

ACtrafficengr:

How do you post photos? I got some interesting shots.

It's a miracle that the span didn't go down.

I'm not sure if you can upload your own photos, but you can link to online photos. Click on "Process TGML" below for instructions.


I should have mentioned those photos are from the Albany Times Union website.  

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      "Come to think of it, there are already a million monkeys typing on a million typewriters, and the Usenet is NOTHING like Shakespeare.

       - Blair Houghton

The pictures are from a friend; I don't know where he obtained them.


From the photos I have, it appears that the rockers for the span on the right (first photo in AC's post)were over- extended (in expansion) and as a result the left span was pushed off its pedestals. Prior to the incident, the bearings for the left span  were grossly overextended in contraction, which could explain why there's a rocker with its base pointing to the right.

The left span is being in place by a wing and a prayer or literally a two inch length of the bottom flanges.

Can someone redo the photo showing the various ramps?  The link seems to have gone bad.

Hg

Eng-Tips guidelines:  FAQ731-376

The newspaper probably removed it from their website.

The latest I've heard is:

The 90' high pier is 21" out of plumb at the top

The temporary supports are almost complete. Soon they will take the weight off the pier, and start trying to figure out why it moved.

They will most likely demolish the pier and rebuild it.

The span that droppped in continuous at the next pier, and may have been overstressed. They have yet decide whether to repair or replace it.

I suspect there will be an extensive study and a voluminous report written about this one.

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      "Come to think of it, there are already a million monkeys typing on a million typewriters, and the Usenet is NOTHING like Shakespeare.

       - Blair Houghton

This collapse seems to be triggered by lack of maintenance and somehow missed (or wrongly assessed) apparent problem with the tilt of the pier. The fact, that two adjacent spans, contracting and expanding in the opposite directions, have the rockers tilted same way, indicated the existing tilt of the pier.
As the rocker bearings used on this bridge, are of hinge (socket) type at the top, and true rocker (roller) at the bottom, the displacement of the span is facilitated by rotation in the socket at the top, and rolling at the bottom. Corrosion in the socket could prevent the rotation to the extent that the displacement of the bridge will be accommodated by the flexing of the pier, or footings.
I have seen similar behavior on several different bridges, when each expansion/contraction cycle increased tilt of the rockers, already inclined in one direction, as the pier slowly was creeping due to presence of steady horizontal force at the top. It would be interesting to see, if any records of the tilt of the pier exists.

Currently on the NYSDOT website:

NYSDOT: DUNN MEMORIAL BRIDGE RAMP TO REOPEN IN MID NOVEMBER

Technical Report Findings Released from Extensive Investigation and Find Convergence of Factors Caused Ramp Shift

http://www.dot.state.ny.us/news/2005/102105b.shtml

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     "...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

              Wm. Phelps Eno, ca. 1928

Forensic report is on NYSDOT's website. It's interesting that they released this information, but they don't discuss why they didn't act when several consecutive biennial inspections showed the bearings were extended.  

Quote:

The failure resulted from the loss of support provided by Pier 11, causing the two spans carried by it to displace vertically. This can be attributed to the unique combination of all of the following factors:

    
• Development of improper bearing alignment of the Span 12 bearings due to shifting of the Span 12 superstructure combined with some initial lateral deformation of Pier 11,

    
• Eventual loss of proper function of the Span 12 bearings,

    
• The high degree of flexibility and flexural properties of Pier 11 in the direction longitudinal to the bridge.

    
• An initiating event that was likely induced by thermal movements or possibly traffic loads.

http://dot.state.ny.us/structures/manuals/dunn_failure_report_10-05.pdf

http://dot.state.ny.us/structures/manuals/appendices_structural_%20forensic_report_10-05.pdf

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     "...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

              Wm. Phelps Eno, ca. 1928