2005 Albany bridge near failure 5

[engeon]

bridgebuster:

I taught geological engineering at the Univ. of Illinois, Urbana-Champaign and I am interested in the abnormal position of rocker bearings on bridges. We have evidence that valley walls and floors in E USA sometimes move towards the center of valleys in response to horizontal stresses in the rock mass.

Could we start a chat about the details of the subject near failure?

Sincerely,
Engeon

 

[hokie66]

Is this the one?

https://www.dot.ny.gov/portal/page/...nuals/dunn_failure_report_10-05.pdf?nd=nysdot

 

[bridgebuster]

That's the report.

 

[engeon]

Hokie66 and Bridgebuster:

I appreciate the reference; in fact I already have it. The problem, as I see it, is that movement of the piers is dismissed outright, but I think some accurate inter-pier measurements may reveal something. We don't expect to see very obvious evidence of differential displacement between pier and surrounding foundation. In fact, pier and surrounding foundation may have moved as a unit. Do you gentlemen know if the tipping of the pier and the annomalous rocker positions are conosistent with ground displacemnts toward the center of the valley?

 

[hokie66]

I know nothing about it and had never heard of it. Just found the report out of curiosity.

 

[engeon]

Wiktor:

Back in 2005, shortly after the Dunn Memorial Bridge incident you posted the following:
"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."

Is there a reason for ruling out the presence of a force in the opposite direction at the bottom of the piers?

Thank you

 

[msquared48]

WOW!

I guess my qauestion would be why was nothing done to try to arrest the situation when it was first discovered several years earlier? Seems like a few people were sticking their heads in the sand...

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[bridgebuster]

"...why was nothing done...?" - Human Nature

 

[Artisi]

" "...why was nothing done...?" - Human Nature" She'll be right mate, no worries, just keep your eye on it.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[wiktor]

Engeon,
No, there was no reason to rule out the presence of the of the force at the base of the pier.
However, the movement of the underlaying subststrata would be rather unsignificant for the typical viaduct spans (80-100 ft) and relative displacements of the piers for simple supported structures.

 

[Qshake]

Movement of the overburden and even underlying rock is always a concern and has shown as a cause for tilting of piers in two projects I've been involved with. One project was out in Northwestern Montana and the bridge spanned a gorge of varying steepness. However in one location for one pier the steep slope and geological strain caused big problems for a rathar shallow existing footing.

In other cases where bridges span rivers there can be a tendancy for the overlying soil to move downward toward the river over time. If this movement is moderate and overtime many years, it can go unnoticed. It often takes aerial photography to ascertain the before and "now" conditions to see such erosion and recognize it as a significant matter.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[engeon]

Thank you Qshake and Wictor, I do appreciate your time and comments.

A relatively little-known fact in E North America (US and Canada) is that shallow rocks are under very, very high horizontal stresses (geological reasons are unimportant for engineering purposes); there are many measurements indicating that a range of 1500-2000psi is to be expected in the free field. In upstate NY and OH,concrete structures for power projects, poured directly against rock, have been destroyed by creeping rock. Horizontal displacements of several inches have been measured (NB: Wictor). Rock bursts are common in tunnels and other excavations which concentrate stresses. There are many examples of these horizontal stresses sneaking up on projects because we don't think about them.

When a valley is carved, the stress trajectories are deflected downward under the valley floor where stress concentrations factors can exceed 2. Sometimes compression folds (buckles) develop in the rock in the middle of the valley floors.

Let's assume a hypothetical single-span gird-bridge,simply supported on two piers, and two approach ramps, also supported by those piers; the bearings are high rocker type. The rocker bearings are found "frozen" as follows: the ones supporting the main span are badly over-extended (main span has dilated more than reasonable computations show); the ones supporting the approaches are badly over contracted. This behavior can be easily explained if one accepts movement of piers toward the valley center. In fact I think this is the case at the Albany bridge but pier movement is discarded outright in the forensic report. Problem is ground movements can be exceedingly difficult to identify and isolate in the field.

The often-cited cause for over-tilted, frozen rocker bearings: detritus, debris, soil, rust, on one side of the bearing
plate impeding rocking action and creating a ratcheting action does not cut mustard with me.

Happy end-of-year holidays

engeon

 

[wiktor]

Engeon,
I recall at list one bridge with the rockers in abnormal position and almost vertical piers (almost because I have no equipment to exactly verify the plumness of the piers).

As the bridge spans typically do not shrink or elongate, the only explanation for unusual position of the rockers will be displacement of the supports.

I was reading linked Albany’s viaduct report before and I did not think that the plumness and exact distance in between piers was ever verified. The tilt of the rockers in one direction could be only explained by:
a. Permanent tilt of the pier
b. Displacement of the pier foundation

I never think that braking or centrifugal forces could permanently displace the bridge of this size. Thermal movement definitely could do, so the creep of the underlying rock. Quick verification of the exact distances in between the piers, top and bottom, could yield some surprising conclusions.

Thank you for bringing up this interesting subject for discussion. It is always more interesting than explaining load distribution factors or basic codes to neophytes.

 

[bridgebuster]

Engeon - interesting theory.

Artisi - I wasn't making light of the situation. The problem was first observed in 1985 - 20 years before the incident - but nothing was done.

 

[MikeHalloran]

Are these rocker bearings typically installed in such a way that a small crew can relieve the load and reset the rocker without taking the bridge out of service?

E.g. with pier tops a little extra large in both directions to allow for some random displacement of the pier, and enough space to set a man-portable jack next to the rocker, with no crane and no cribbing?





Mike Halloran
Pembroke Pines, FL, USA

 

[engeon]

Wiktor, bridgebuster:

I thank you gents for the time and interest. I am looking for suggestions on how to accumulate field data to put flesh in the theory and see if it holds water. Are there sources of info within the various E USA state DOT's that I could approach? Any cases you know about besides Albany?

Your suggestion to make accurate and precise measurements between piers is a good one, Wiktor. The problem is that, as in the case of the Albany bridge, all you read in the report is something like "we found no evidence of pier displacement". Period.

I remember asking one of the I-35 W, Minneapolis guys if they had any plans for that type of measurements, and his answer sounded like: Of course, you idiot, we know what to do" but I have not found any details on inter-pier measurements that ruled out the mechanism I am proposing.

 

[engeon]

Not a bridge engineer, Mike, sorry.

 

[Qshake]

MikeHalloran - Contemporary bridge design and construction would not skimp on the bearing shelf the way our predecessors did. Thus this is not often an issue these days. Also it is never easy to simply jack the span and reset the bearings. Typically it is industry standard to remove the live load and jack. It is also industry standard to include live load in the jacking calculations.

engeon - On the matter of I-35W, you need to do more digging as there was most certianly pier tilting caused by movement of the overburden toward the river. As I recall this was on the side where the railroad tracks were. The expansion devices were locked up and in some cases the ends of the girders had to be cut to allow more expansion. Piers were noted as tilting for several years prior to collaspe. I don't know the report but if the information site is still up suggest you check that out. While I can see this not being the main failure, that doesn't mean it wasn't a contributor. A contributor that in a sense locked up the entire south approach preventing the bridge from expanding as it needed to. This would have caused stress in the members that may have contributed to an overload situation....

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[engeon]

Qshake:

Many thanks for the thoughtful comments and advise. I will follow them; particularly now that the dust has settled. I couldn't agree more regarding the role of possible geo-induced displacements further loading the structure. That is what I have strongly suspected from the beginning. Any tilting of the pier top away from valley axis would have loaded additionaally the lower arch membere in tension.

Gratefully,

engeon

 

[wiktor]

MikeHalloran,
Reliving the load from the locked bearings is rather tricky, as the energy stored could become uncontrollable.
On the other hand on the same subject, I'm suspecting that suddenly released bearing took down Minnesota Bridge, initiating the movement and collapse.

Engeon,
Approach spans on the Queens side of B-W Bridge had large displacement of the rockers. This should be well documented over the years and the managing agency has excellent technical library with all reports.
I will also suggest contacting NYS DOT Structures, and checking data base of existing bridges for displaced rockers or bearings.

Qshake,
I agree that the creep of the support was only contributing factor in the I-35W collapse. Other overlooked items include
paved over relieve joints in the deck, frozen sliding bearings for the deck stringers, and in general, thermal and displacement stresses in the structure of this magnitude with frozen expansion bearings.
And we all have to remember that one "expert" report desribed this bridge as somehow redundant and likely capable of withstanding major member loss.
(

http://www.dot.state.mn.us/i35wbridge/pdfs/umn-study-fatigue-evaluation-br9340.pdf

- scroll to page 10)