×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Bridge Collapse in MN
29

Bridge Collapse in MN

RE: Bridge Collapse in MN

I went over it about 2 hours before. It is a good thing it happened after rush hour and not all lanes were not open. I think there might be as many as 8 lanes total in some areas if ramps/acceleration lanes were included.

Built in 1967. Steel main span over the river with simple spans north and south. The entire section of freeway (several miles) was undergoing surface and other repairs. Some lanes on the bridges were closed and some construction equiment was deployed on portions of the other unused lanes that were under repair.

The collapse apparently started on the south end and progressed northward. Somce sections went quickly and other much slower as people had already stopped. At some expansion joints one side went up and the other went down. The intersting thing was that there was a lateral movement or twisting of some of the spans instead of just vertical.

It will take a good independent professional study to determine the real cause because it was obviously not subjected to classic highway loading conditions.

RE: Bridge Collapse in MN

2
Someone on the Fox news interviews stated they drove over it right before it fell and they saw the construction workers had punched a large hole through the deck.  Did you see that?  They said there was expansion joint repairs going on but the hole in the deck "didn't look right".

RE: Bridge Collapse in MN

Here's a photo of what the bridge used to look like:



RE: Bridge Collapse in MN

More photos are on the NYTimes web site.

RE: Bridge Collapse in MN

Sounds like the jackhammering vibrations of the deck slab for two months may of caused the sudden failure of a bridge.

RE: Bridge Collapse in MN

2
Apparently this bridge was studied fairly extensively in 2001.  See below for a link to a report done by the University of Minnesota.  The report details extensive fatigue analysis studies including SAP 2000 analysis and field testing comparisions under both controlled and open traffic conditions.   

One of the conclusions being "Since the measured and calculated stress ranges were less than the fatigue threshold, it is concluded that fatigue cracking is not expected in the deck truss of this bridge."

http://www.lrrb.gen.mn.us/PDF/200110.pdf

I'm sure this will get pulled soon....

RE: Bridge Collapse in MN

Star Tribune in Minneapolis released some info on the bridge inspection report.  The bridge was rated structurally deficient.  Sounds like there were some poor fatigue details on these trusses.  

http://www.startribune.com/10204/story/1338970.html

RE: Bridge Collapse in MN

WillisV,
Is this the same report that CNN was quoting that determined that there was no redundancy in two planes of the structure and that fatigue would be problem?

CNN also had a professor of civil engineering that went over the design, steel-arch, of this bridge in detail. He summed up his discussion with the statement that in this particular design it only took the failure of one member the truss to cause complete failure.

RE: Bridge Collapse in MN

I was down there yesterday just after it happened and it was surreal to see that there was just no bridge there where there used to be one. Unfortunately someone with our knowledge couldn't help much as it was a complete collapse.  From watching the video I see an almost perfectly symmetrical, and instantaneous, collapse of the main span.

My own 2 cents freom what I saw (and I know there will be a lot of this)

You just don't see failures initiate and progress perfecly symmetrical within a span like that, leading me to believe that the collapse must have begun on the backspan.  It is almost certain that the main span needed the moment contribution from the back spans.  Two plausible scenarios are a local deck failure that dropped and the falling mass energy took out an important backspan truss member on the south side, or a failure within the truss at that location, leading to progrsssive collapse on the south side of the south pier, and a complete failure of the main span as a result of unforseen moment deficiency.      

RE: Bridge Collapse in MN

Additionally, the visible failure or the north side of the main span seems to progress as shear failure at the within the truss at the north abutment, but the south side seems to already be moving, and ahead of the north side.  It is plausble that the failure mode seen at the visible abutment had already occurred at the one just out of the picture.

RE: Bridge Collapse in MN

2
great thread.  

Is anyone else having problems reading the right end of everyone's posts?  Or is it just me?

RE: Bridge Collapse in MN

I can read the page fine. Have you tried viewing some other web pages?

RE: Bridge Collapse in MN

cedent, yes.  It's just this thread for some reason.  Usually, there is a scroll bar at the top or bottom of a page that won't fit within the window, but not this time.   Odd.

RE: Bridge Collapse in MN

2
SteelMover - I'm looking at a birdseye view in Local LIve. Are the backspans (anchor spans) cantilevered to support the approaches?

RE: Bridge Collapse in MN

archeng59.

I'm having the same problem.

RE: Bridge Collapse in MN

I think its the big picture - it has blown the browsers.

csd

RE: Bridge Collapse in MN

I did not see the CNN report, however, based on a discussion with a co-worker, I believe the person they interviewed was Retired Professor Ted Galambos.  Professor Galambos was a long time member of the University of Minnesota Engineering Faculty.

RE: Bridge Collapse in MN

It is somewhat obvious from the video that the bridge failure occurred where the construction crew was working.

If you look at the pictures, it appears that new concrete on the bridge deck is covered with visqueen. There was supposed to be a thunderstorm later that night.

What happened to the construction workers?

RE: Bridge Collapse in MN

The cantilevered spans were only about 37' at each end.  The main span is 456' with 265'approach spans at each end.

I tried downloading the report that WillisV posted but it is very slow and never finishes.  But from what I read, fatigue is a very real issue with this structure.

RE: Bridge Collapse in MN

From the way it dropped straight down, it doesn't seem like it would be a fatigue or fracture failure.  What are the chances of both trusses going at the exact same time?  If one failed, it would start falling first and twist the bridge and bring down the other truss.

I suspect foundation failure most likely due to scour.  Even though the piers were at the edge of the water, it still looked like they were in the water.  I guess it's that or something in an adjacent span that pulled or pushed the main span off its bearings.

It still seem weird the way it dropped straight down.

RE: Bridge Collapse in MN

I have the same problem reading the right end of the posts. Can the poster of the picture resize it?

RE: Bridge Collapse in MN

In my previous post the professor that was giving commentary concerning the UM report and the design features of the bridge mentioned something about the connections at he the ends. I didn't catch all his comments but he was worried about the ends being pinned or not being pinned. He tried to clarify this and was rudely interrupted.

He also stated in it's day this was a every inexpensive way to construct a bridge, less steel and lots of labor. Today it would be very expensive construction due to labor cost.

Some of you bridge guys help me out a little on this one. He also made the statement that this type of truss would fail completely if any one component failed.

RE: Bridge Collapse in MN

If you look at the picture above, it looks like they were pouring concrete.

Maybe, the concrete formwork collapsed onto a lower structure member.

RE: Bridge Collapse in MN

RichBridge - I had the same thoughts (although I am definitely NOT a bridge expert).  What was the name of that bridge in NY that short-sheeted itself a while back? (when the pier shifted slighly from scour, moving the beam support just enough to cause a chain reaction with the spans).  Could some minor shift of occured and somehow gone undetected?  If so, could a hot day's expansion, evening rush hour and the construction have aggrevated the problem? Sorry if these ideas are way off base--I'm a water person (and an occasional structural wannabe)

RE: Bridge Collapse in MN

It still seem weird the way it dropped straight down.

Gravity

sorry....I couldn't resist!

RE: Bridge Collapse in MN

I'm aware that structural analysis software have birth/death options for structural elements, but do they also automate the death of such elements in order to check for redundancy due to the failure of random elements?

RE: Bridge Collapse in MN

OK - I resized it and deleted the other one.  I'll red flag that post and get it deleted.

Here is the 1/2 sized photo...hopefully this will work better.



RE: Bridge Collapse in MN

The piers are on land and from the pictures do not look like they shifted. You can clearly see the north end piers sticking out of the debris in this picture.

The entire bridge did not fail straight down. If you look at the picture below, the bridge did not come straight down at the north end. The debris at the north end of the bridge shows that the top of the north end of the bridge fell or twisted to the west.

The south end of the bridge came straight down, following the failure of the north end.




RE: Bridge Collapse in MN

Bird poop and de-icing spray.  I can remember back in college at the U of M they had massive problems with bird droppings in this bridge due to the open tubes used for the trusses.  They would have to constantly clean out the corrosion from the droppings.  A couple of years ago they even installed plastic caps on all the openings to prevent nesting.  Then a couple of years ago, they installed a new de-icing system that sprays down the bridge everytime it snows.  This was an experimental formulation at the time.  My guess is corrosion is going to be the culprit.

RE: Bridge Collapse in MN

In the photos on the Yahoo website, on the other end of the bridge, the entire portion of the pier above ground is tilted toward the river.  

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: Bridge Collapse in MN

Some of the commentary about the event on news programs has been incorrect.  The photo shown above by BIMR is of the south end of the bridge.  Locks are on the south side of the river here, train tracks are on the north side.  The video footage looks like it was taken from a camera that looks at the locks, and is facing north.

RE: Bridge Collapse in MN

After going to school within a miles or so, being around the hydraulics laboratory that is near there on the north/east bank, boating and fishing for smallmouth bass, I would think that the piers are probably  onon the limestone ledge that is common all through the area.

Thst stretch of the Mississippi river is not typical of the area below St. Paul (10-15 miles downstream by water). It ihas lower flows and is carved out of the limsestone that very close to the surface.

Sorry, but I could not see all of my post for corrections

RE: Bridge Collapse in MN

IRstuff,

I was just watching the news and they showed the same thing, the support on one end is leaning toward the river.
It showed the support in the water.

I was having trouble with whether this was a camera angle problem or the real thing. They came back to this area in another shot and sure enough the support is leaning.   

RE: Bridge Collapse in MN

Thanks for resizing the photo, JAE.  But the original photo is still causing something to be messed up.  Doesn't really matter.  I can get the gist of what's being said.  

RE: Bridge Collapse in MN


Didn’t the bridge have a center pier in the water?  It looks like it from the one photo.  I tried to confirm this from Google Earth, but all I got was a Salvador Dali version of the bridge, melted-looking.  

I watched the news conference with the engineers.  I believe they mentioned corrosion at the roller bearings.  I haven’t worked in bridge engineering for awhile, but this seems worth investigating.



"If you are going to walk on thin ice, you might as well dance!"

RE: Bridge Collapse in MN

I think for sure the collapse is originated from the middle span.

Never, but never question engineer's judgement

RE: Bridge Collapse in MN

There was center support as the arch spannnd (463 ft)to not impeded the river traffic.

Checkout the post by JAE at the top of the page

RE: Bridge Collapse in MN

I dont see any center support.  The supports are on both sides of the river.

Never, but never question engineer's judgement

RE: Bridge Collapse in MN

You are correct, I had the bridge ends incorrect. Lets try again. The piers are on land and from the pictures do not look like they shifted. You can clearly see the south end piers sticking out of the debris in this picture.

The entire bridge did not fail straight down. If you look at the picture below, the bridge did not come straight down at the south end. The debris at the south end of the bridge shows that the top of the south end of the bridge fell or twisted to the east.

The north end of the bridge came straight down, following the failure at the south end.

If you look at the picture above, it looks like they were pouring concrete.

Maybe, the concrete formwork collapsed onto a lower structure member.

Does anyone know what that truck is by the concrete hauler.?

NY Times Picture:


Wikipedia Picture:


NY Times Graphic:

RE: Bridge Collapse in MN

The MSNBC link was very informative, espically the profile view of the collapse. The illustraton shows a cantilever truss that would have been constructed from both ends simultaneously cantilevering from the end spans and meeting in the middle.

One problem with the graphic is that the location of the railroad tracks is different in the birds eye and profile views. My understanding is that the tracks are between the end piers.

RE: Bridge Collapse in MN

Dr. Dexter's 2001 report summary:

Bridge 9340 is a deck truss with steel multi-girder approach spans built in 1967 across the Mississippi River just east of downtown Minneapolis. The approach spans have exhibited several fatigue problems; primarily due to unanticipated out-of-plane distortion of the girders. Although fatigue cracking has not occurred in the deck truss, it has many poor fatigue details on the main truss and floor truss systems. Concern about fatigue cracking in the deck truss is heightened by a lack of redundancy in the main truss system. The detailed fatigue assessment in this report shows that fatigue cracking of the deck truss is not likely. Therefore, replacement of this bridge, and the associated very high cost, may be deferred.

He discusses scary fatigue details and pigeons as identified above by concretemasonry. The report maintains that the truss has a severe lack of redundancy. South approach span initiation still looks credible.

RE: Bridge Collapse in MN

2
This might be relevant -- I haven't seen it cited yet.
http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_354.pdf
Inspection and Management of Bridges with Fracture-Critical Details, Transportation Research Board, 2005

Co-author is Robert Dexter who worked on the 2001 Mn/DOT report.  

RE: Bridge Collapse in MN

The construction semi truck trailer is right in the middle of the area that collapsed. Is it possible that the bridge collapsed from being overloaded?

"Sloan said his crew was placing concrete finish on the bridge for what he called a routine resurfacing project. "It was the final item on this phase of the project. Suddenly the bridge gave way," he said."

For what purpose are the semi truck and loaders used? It looks like it was a material staging area. Is the truck for asphalt, sandblasting, or concrete deck repair?

Milwaukee Journal Picture:


Another Milwaukee Journal Picture of the truck:


Here is another of the construction trucks that look similar to the crashed one.




RE: Bridge Collapse in MN

I watched the CNN video from the security cam and heard the anchorwoman comment something to the effect, "you can see the smoke as the bridge hit the river". I am thinking, oh jeez, here we go again with the thermite conspiracy wackos.

RE: Bridge Collapse in MN

The workaround for those with RHS of page truncated is to increase display sttings, e.g., from 1024x768 to 1152x864 pixels.  The issue has been discussed before; as Eng-Tips controls neither linked photos or user displays, it would be impractical to resize wide images.

RE: Bridge Collapse in MN

RE: Bridge Collapse in MN

It appears that some of the earlier investigtions included a fatique evaluation.  Three basic members were determine critical.  These evaluations were using Miner's rule. Does anyone know the material and its transition temperature of the basic truss?

I did not see any K1c evaluations, only stress range.

It would seem to me that a structure subject to -35F could have crack propagation problems that could cause accumlative fatigue that could later cause problems during the summer months.

RE: Bridge Collapse in MN

3
There is more (better) techincal reporting on ENR.com.

Regards,
Qshake
pipe
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Bridge Collapse in MN

In the picture above showing the leaning support it looks like it has twisted also. if you constructed a plane through the center line of columns if would be funny looking. This maybe because the bad looking one is on the up stream side.  

RE: Bridge Collapse in MN

Mtnengr - For a good example of crack propagation due to material temperature see the Hoan Bridge failure in Milwaukee. It was really cold when that happened. Three girders had fatigue cracks propagate clean through.  Though it didn't fall due to catenary action in the deck. It is believed temps played a role there but the 90+ degree day we had here would not support temperature embrittlement, at least not with the event that finally broke the camel's back.


RE: Bridge Collapse in MN

I watched the CNN video repeatedly, and I noticed that there is clearly a time delay between the main span collapsing, and the approach span collapsing.

I am not sure what that means--did the collapse of the main span precipitate the collapse of the approach spans?

DaveAtkins

RE: Bridge Collapse in MN

Quote:

did the collapse of the main span precipitate the collapse of the approach spans?

That looks like what happened at the north end. With the main span gone the approach span could collapse. I imagine this is why the pier is pushed towards the river - the approach spun thrusted it out of the way as it progressed through its collapse.

RE: Bridge Collapse in MN

Of course the piers on the north end are leaning.

However, if the north end piers were leaning and imitated the collapse, the collapse would have started on the north end.

But the CNN video clearly shows the collapse started on the south end. After the main spans collapses, a pause occurs before the north approach span collapses. It is logical that the collapse of the north approach span pushed the north end piers off center.

RE: Bridge Collapse in MN

Inspection reports and studies of the bridge are on the Minnesota DOT website.
http://www.dot.state.mn.us/

RE: Bridge Collapse in MN

Let’s hope that good will come from this tragedy: That the scores of “concerned” politicians will actually address the problems with this country’s infrastructure and not forget what happened after Election Day passes.

In the meantime, we should avoid public speculation on the collapse. As some one noted there is a lot of incorrect information in the news. Some ludicrous statements I’ve noted:

“State bridge engineer Dan Dorgan said the bearings could not have been repaired without jacking up the entire deck of the bridge. Because the bearings were not sliding, inspectors concluded the corrosion was not a major issue.”  IF THE BEARINGS WERE NOT SLIDING THAT IS A PROBLEM!

"I would be stunned if this didn't have something to do with the construction project," said David Schulz, director of the Infrastructure Technology Institute at Northwestern University. "I think it's a major factor." STICK TO TEACHING!

“This bridge is unique because it was constructed with a single 458 ft steel arch to avoid putting piers in the water which would impede river navigation, according to the U.S. Dept. of Transportation. “ I GUESS THEIR DICTIONARY HAS A DIFFERENT DEFINITION OF UNIQUE.

RE: Bridge Collapse in MN

I am not a bridge expert.  So do you think the support is suppose to be free to slide (slotted maybe?) or do you think it is bolted down?  Maybe the pier moved when the bridge went down, not before.

Never, but never question engineer's judgement

RE: Bridge Collapse in MN

Yelp!

Here is another approach to the detection and monitoring of fatigue cracking on steel structures in real time. I would imagine that all such approaches to automating detection and monitoring of cracking will have tons of money dumped on them shortly.

http://www.matechcorp.com/index.html

RE: Bridge Collapse in MN

Wikepedia's description yesterday said that there were "geared wheels" to accomodate expansion. I cannot locate that decription today.

RE: Bridge Collapse in MN

The problem with these technologies is LAWYERS.  We actually tried to do this with stadiums, but we were cut off because there was too much liability involved.  Your entire organization would be hung unless legislation was passed that barred the possibility of lawsuits against engineers as long as good faith (no bribes, gross negligence, etc.) was in place during the monitoring. I guess the only thing you can do is tell the DOT whats wrong and indentify nothing as "Safe" or "Acceptable".  You all can imagine where the first fingers would point though.

Unfortunately politicians are almost all lawyers, who want to find blame in the engineering not the funding....  

RE: Bridge Collapse in MN

so does the geared wheels have a stop on it?  Can this geared wheel pull on the pier when it collaps? Can you also lift this gear up or is it restraint up?

Never, but never question engineer's judgement

RE: Bridge Collapse in MN

Normally, expansion bearings have keepers that limit the maximum movement allowed and I certainly would expect that to be in this case also.

During a collapse situation damage can occur to the pier, expansion bearing, and other elements that will obviously make it act differently then under normal conditions. The trick is to find out the chain of events from all the different broken, tilted and twisted pieces. Which happen first?

RE: Bridge Collapse in MN

Go to Page 2-3 (37 of 100) of the URS report (Volume 1 of 3), there are photos of the expansion bearings. You'll see what was referred to as "geared wheels". Essentially, it's a roller nest. I've seen some unusual bearings but I've never actually seen one quite like that.

jike is absolutely right, the chain of events needs to be established.

RE: Bridge Collapse in MN

On the MATECH web site, the bridge on the left appears to be I-20 over the Mississippi River, in Vicksburg. I worked for the engineer who designed it. He used that design as the basis for the replacement of the original Silver Bridge in West Virginia.

WVDOH needed a set of plans quickly and when they learned that length and channel clearance of Vicksburg Bridge was more or less what they needed, he got the job.

RE: Bridge Collapse in MN

To add to bridgebuster's list of ludicrous statements above, we have a local weatherman here in the Twin Cities who has been freely speculating on the collapse during his weather forecasts, because:
1.  He must consider himself qualified because he took some science classes;
2.  He said his wife is an Architect, who had to take some structural engineering classes in school (many years ago).

His (and her) theory is that the vibration of the train running below the bridge at the time is the main culprit, along with the rush hour traffic.  Somehow, I don't think it was the first train to use those tracks during rush hour!

(I guess that makes me a Meteorologist, because I have a rain gauge and thermometer in my back yard).

RE: Bridge Collapse in MN

denoid.. maybe the frequency of the vibration of the train plus the frequency of the jack hammer matches the frequence of the bridge!  smile

Good news, they reduced the number of missing people from 30 to 8.  5 people are dead so far.  I hope there are not a lot of people walking under the bridge when it happens.

Never, but never question engineer's judgement

RE: Bridge Collapse in MN

In the video of the collapse it shows a lady in a rapid exit screen left, barefoot. She must have been very close to the bridge when it started to fall.

RE: Bridge Collapse in MN

"maybe the frequency of the vibration of the train plus the frequency of the jack hammer matches the frequence of the bridge!"

Maybe, but I'd rather hear it from someone other than the TV weather geek.  

RE: Bridge Collapse in MN

(OP)
My thesis is in train-induced vibrations (in buildings mind you)... but if this guy is serious keep in mind that even the train vibrations would need to travel through the soil, up the peirs/abutments, through the bearings pads (which will act as isolators or very high dampers) then into the bridge.

The magnitude of vibrations would be so small that resonance caused by the train is highly unlikely to bring the bridge down.

I think this guy watched one to many tacoma narrows specials

RE: Bridge Collapse in MN

I guess my main point is, as bridgebuster put it nicely:   "we should avoid public speculation on the collapse. As some one noted there is a lot of incorrect information in the news."  The media is obviously looking for scapegoats to blame right now.

Having an obviously unqualified media person (weatherman) give theories just doesn't help anything.  I'm a building structural engineer (as opposed to a bridge structural), and I wouldn't dream of giving any speculations to be aired in public right now, because I just don't feel qualified enough in that area.  I'd rather hear what the true experts with experience in bridge design and/or collapses have to say.

The only good to come out of this right now is that it maybe brings some attention to a possibly dangerous condition in other bridges around the country.  At least they will be looked at and re-evaluated.  The politicians sure seem to be congregating in Minneapolis this week.  They know, after Katrina, that how they respond might just have an effect at the polls in the very near future.

RE: Bridge Collapse in MN

unclesyd, that was a good observation on the woman in the video although she is not barefoot. She was only about 100-120 feet away from the bridge.

The thing is, during her entire 15 seconds of fame, it looks like she never stopped talking on the cell phone during the entire collapse of the bridge. Amazing concentration!

RE: Bridge Collapse in MN

Denoid -

Your statement about the Guy's wife being an Architect got me thinking.   Has anyone ever seen the intro for Building it Bigger on the Discovery Channel??  The host claims to know alot about engineering because he went to Architecture school.  What a joke!!!

We need to let the engineers on the ground do the investigation and keep the speculation to a minimim as the drive-by media types will run with antyhing that they can use to make someone look like a scapegoat.  

Hopefully what will come out of this is an is an increased knowledge, and a greater awareness of the poor state our infrastructure is in.  I can believe the numbers being stated of how many bridges in the country are deficient, however, the media does not understand what alot of this data means, which is dangerous. ASCE has been publishing for years the condition of the infrastructure and a believe that our bridges normally get C's and D's.    

RE: Bridge Collapse in MN

I am in complete agreement with the opinion that many “news reporters” are far beyond their expertise or knowledge. I guess they have to fill air time and have a hard time shifting from “entertainment reporters (ala Paris Hilton antics)” to real hard factual news reporters where they should seeks facts and professional opinions. – One female network personality was describing the “concrete” bridge and how difficult it will be to get the cars and debris out of the very, very deep water (actually, the barge channel is only 9’ deep as I recall).

I felt the response by officials (NTSB, MNDOT, etc.) to collect all historic information, photos and videos, interviews and recovering the debris to determine the real cause was a very positive step. It could be very valuable to the engineering profession.

It sounds like it will be a big project to visually reconstruct the bridge and examine the salvaged components. Despite the current, the odds on collecting all the major components are quite good. The river bottom is quite hard and is native limestone in many places; the depth is not that great (9’ barge channel) and the flow (in terms of volume) is not as great as you would expect. Just downstream there is an area where some debris that was flushed away will collect. – Maybe they will reconstruct it just like an airplane forensics project.

They are currently putting GPS equipment on all of the pertinent points of the structures to determine the present location before anything is moved.

After they get the physical components, they will then have an opportunity to look at the failure points (probably multiple sequenced failures) and then look at the possible causes including the unbalanced loads, vibration, effects of any repair efforts and “terrorism” without the “benefit”(?) of the newscasters and limit the investigation to the engineering facts.

This will hopefully be documentation to put teeth into the move to conduct engineering evaluation of all infrastructures for once.

Dick

RE: Bridge Collapse in MN

The woman in the video on the cellphone was identified (maybe on ABC's Nightline?); she was reporting the collapse to 911.
Far better than some TV 'personalities' discussing  frequencies!

RE: Bridge Collapse in MN

Does anyone think that new information will change anything?  

Here is the most traveled bridge in Mn with known deficiencies and the official stance was wait and see what will happen.

The only news reporter that appeared to have any inkling of what was going on was Greta Van Susteren. She asked a questions about the stresses it would take to cause such a failure.

RE: Bridge Collapse in MN

unclesyd -

Maybe it will shed light on the fact that our infrastructure is in dire need of repair.  If it were not for this tragic incident, the general public would probably not be aware of this, or pay much attention.  Maybe we can actually get congress to fund some transportation projects.

RE: Bridge Collapse in MN

Sure our infrastructure is in dire need of repair and money. So is everything else, schools, social services, even defense (can't vouch for it, one think tank guy on the radio claimed we were eating up the service lives of so many of our military systems, that it would take $1 trillion to replace it all). I heard an estimate of $180 billion to replace the bad bridges. Where's that money going to come from? NCLB (No Child Left Behind)? That new prescription drug benefit for seniors from a couple years ago? Get rid of all of those programs, and you aren't even close to having enough. For all of you who say there is 'dire need,' tell us where you would get the money? Who would lose their funding so we can repair all the bridges?

I didn't mean this to be a political discussion, just want to know where the money would originate to repair all these bad bridges?

RE: Bridge Collapse in MN

The bridge collapsed in 4 seconds. And from the video, the failure is apparently shear type. It looks like one (or more) web member near support failed first.

RE: Bridge Collapse in MN

Prost -

How about repealing the tax decrease for the wealthiest Americans?

When much of our infrastructure was built, dams, interstates, etc. 30s to 60s the top tax bracket ranged from 62% - 92%.

Now its political

RE: Bridge Collapse in MN

If you can catch the latest update by NTSB Chairman on the bridge failure investigation. This will be an enlightment.

He mentioned that they saw a 50 ft "shift" in the southern end if the bridge and that the southern end maybe the point of interest.

This marvelous computer program they have is an FEA program. He had to read what FEA stands for. They are going to use this to take out pieces of the bridge and see where it falls.

The good news, apparently the death toll is going to be as bad as originally thought.

RE: Bridge Collapse in MN

Look at the numbers--lowering taxes decreases tax revenue in the short term, but substantially increases tax revenue in the long term. This is not rocket engineering--it happened when JFK got tax reductions through Congress, it happened with RR got tax reductions, it happened yet again when GB II got tax reductions. AND, to answer the question of what happens when you Raise taxes, all you have to do is look at what happened with GW I raised taxes; a recession followed. How's that for bipartisan? Lowering taxes stimulates economic activity.

RE: Bridge Collapse in MN

And deteriorates infrastructure

RE: Bridge Collapse in MN

Did anyone else notice that the bridge seemed to come apart just south of the Contractor's semi-trailer cement truck and mobile mixing trucks (truck with white cab) as seen in these Journal Sentinel photos:



The center of the bridge also appears to have split and zippered apart down the middle of the deck. The split is widest near the mixing truck.





RE: Bridge Collapse in MN

When I look at the video in stop motion, I believe I see a wave traversing the bridge from the unseen far end (my assumption being that there has been a partial collapse at the unseen end).  When the wave hits the visible end , the truss breaks at the pier then a wave (or collapse) moves in the opposite direction.

I think the speed of the wave make the bridge appear to be falling straight down in real time.

RE: Bridge Collapse in MN


Hey, not all architects are sitting around picking out pretty colors!  When I got out of school, with a BS/Arch, I went to work for a structural consultant that specialized in  erection procedure and failure analysis.  I modeled failures as well as inspected may structures, from waste digesters to bridges, for all types of distress.  I’ve spent long hours in a crane or manlift in Chicago winters trying to find stress cracks in steel structures.  I spent seven years doing structural steel shops drawings.  My boss was a former chief engineer at American Bridge and Iron.  It was an excellent training ground.  

Maybe not all architects have had such experience in engineering and failure analysis, and certainly not many female architects, but you can’t start bashing them all or I’m gonna have to start bi!ch slappin’ ya.

Actually, I don’t mean to rant too much, but I don’t like to see the polical/CYA turn the investigation has taken.  I think it taints what should be a purely scientific endeavor, regardless of liability.  Analyze what happened without first looking to see who has the most money or who you can blame for the most political gain.

And I have some really bad news from the West Coast where I no live.  I have received a couple of email from friends I consider intelligent asking me if I heard that it must have been a terrorist bomb and that the Bush administration is keeping secret the real death toll of almost 100 people.  I try to explain the current and far more likey theories, but not many are listening.

My new sign off, “For those who believe, no proof is necessary.  For those who do not, no proof is possible.”


"If you are going to walk on thin ice, you might as well dance!"

RE: Bridge Collapse in MN


As a result of all this, the UK politicians have decided to review the bridges in the Uk (must need something to do!)

Our local bridge (not steel) will no doubt be subject to a major inspection...after all, it's been there since 1674....

http://www.thisiscorbridge.co.uk/graphics/corbridge_bridge1.jpg

Agree with all of above re media "experts". Here in the UK we have all sorts of academics on tv, expounding their opinions (for that's all they are) of the cause of failure of a structure some 2000 miles away. I have yet to hear one say "Let's wait until the Engineer's reports are in". But I suppose that is not "News".

Hope you guys over there sort it out without too many politicians getting involved (have not seen a US engineer on the tv yet!!) Condolences to the families of the lost.


Best regards


Harry

RE: Bridge Collapse in MN

casseopeia-

I'm not bashing Architects, and gender has nothing to do with it.  With the credentials you've listed, you actually sound more like an engineer than an Architect, and I know that there are plenty more like you out there.  You actually sound more qualified than most of the people I heard talking about it in the first 24 hours after the collapse.

But, there are also many Architects who don't do anything more than space planning and color selection, and it's those people I don't need to hear weighing in on this - BECAUSE THEY'RE NOT QUALIFIED, even if they did take a structures class in college 15 years ago.  I would, and will say the same thing about a structural engineer who is designing only, say, concrete foundations or light gauge structures all day...they are certainly qualified in their own area, but not here.  I say the same thing about myself!  I'M NOT QUALIFIED TO BE A TV EXPERT ON A MAJOR BRIDGE COLLAPSE.

Hope that clarifies it for you.

RE: Bridge Collapse in MN

Here is a good one, here in Florida bridge inspection reports are Top Secret by order of Homeland Security. That's OK as the local paper published an article that the public can rest assured that all bridges are in very good condition, quoting the DOT.  

I tried to get a report on a recently built bridge that has been under going a lot repair work since it was commissioned. I kept hitting firewalls and finally had to contact a person who had worked on the bridge. They were replacing the inferior grout that had been used to protect the tension cables, he said tendons. This bridge spans the intracoastal waterway and is 1/2 mile from the Gulf of Mexico.

RE: Bridge Collapse in MN

Is there a structural engineer on this website who specializes in bridge design and analysis who can offer some experience-based insight into the likely reasons for this particular collapse?

Maui

RE: Bridge Collapse in MN

FYI- on the screen size issue- at the lower right of my IE browser is a "Zoom Control"- zzoming to 75% or so makes everything visible, although smaller.

RE: Bridge Collapse in MN

MikeHughes,

Why don't you red flag your second post and get the site management to fix the title of the thread.  I used to live near where the Mississippi flows alongside the state of MS and I crossed that river many times on each and every one of the bridges that touch MS on one end and if one of those bridges fell.........well, you know.  So the title makes my heart jump every time I read it especially the first day before I saw the news and realized that it was MN.  The Mississippi is kind of a pup up there, not to minimize the enormity of the tragedy for those who lost loved ones.

rmw

RE: Bridge Collapse in MN

(OP)
good point.. i just red flagged it

RE: Bridge Collapse in MN

I was trying to find the list of deficient bridges in Minnesota on the MN.DOT Website and went down this road,

http://www.dot.state.mn.us/bridge/StateAidBridge/process/process_a_files/Bridge%20Ratings%20on%20Web_files/Bridge%20Ratings%20on%20Web.htm

The hypertext link,
"Minnesota Bridge Rating and Load Posting Report for County and Local Agencies.. " appearing on this page, with a link to this page,

http://www.dot.state.mn.us/bridge/DocumentsFormsLinks/BridgeRatingAndLoadPostingReports/CountyAdLocalAgencies/Co  

http://virtualpipeline.spaces.msn.com

RE: Bridge Collapse in MN

GUTLESS BUREAUCRATS, NO BRIDGE REHABILITATION "SUPERFUND," INADEQUATE INSPECTION AND EVALUATION PROCEDURES, DESIGNING TO A "NAT'S ASS."

GUTLESS BUREAUCRATS:  They see engineering recommendations as optional!

NO BRIDGE REHABILITATION "SUPERFUND:"  Money and politics should not be a roadblock when it comes to life safety.

INADEQUATE INSPECTION AND EVALUATION PROCEDURES: Bridge engineers should reevaluate their fatigue analysis procedures.  They should replace stress range approaches to damage tolerant crack growth procedures.

DESIGNING TO A "NAT'S ASS:" The bridge designer should be using significantly lower allowable stresses for fracture critical details.



RE: Bridge Collapse in MN

Maui - The last thing we need to encourage is speculation by bridge engineers not familiar with this specific bridge.  There are many different bridges and 99% of bridge engineers today are only familiar with the typical slab and girder overpasses.  It would not speak well of them (or others) to offer opinions on this collapse.

Unclesyd - The Hoan bridge is in Milwaukee!

As I read the posts from the beginning I can't beleive some of the writings actually belong to engineers.  It's true that infrastructure is aging and needs to be dealt with but some of the rants and raves posted here are no better than lay people, media Zealots or meteorologists.

As for Architects - they should also refrain from commenting, shop drawing review or not as should the folks I've listed above.  Experience with steel design especially with buildings be they large, deep plate girders acting as transfer girders doesn't play into this since there is virtually no fatigue cycling in that environment.  Fatigue and Fracture Mechanics is a specialty area of engnieering and those who've had a course in it (as I have) will tell you that it is far from exact science and requires dedicated study.

As for the history of the bridge, we scour what we can from teh web, but has it occurred to anyone that we're barely scratching teh surface?  This bridge could have been retrofitted or rehabbed for other purposes and we have no idea what or how it could have been modified or how those modificatinos affected the original behavior.

So please let's not act like the very people we curse upon hearing mis-information.

Regards,
Qshake
pipe
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Bridge Collapse in MN

Sorry about the problem with locations. It a problem when you get old and try to do two things at once, type and listen to the news.

Qshake,
You and I have been around and about enough to see the same refrain form the bureaucrats when they come out with explanations and hyperbole, along with dancing, around any event such as this. I know that most bridge engineers and professors can't speak out about things like this if they want to keep their job or get grants.

I think it about time more people, maybe not the best informed, get concerned and rant a little until the next bridge fails.  

RE: Bridge Collapse in MN

Qshake, there is a great deal of speculation that has already been offered in this thread by individuals who have made it clear that they are NOT experts in the structural engineering of bridges. If anyone is to offer potential explanations for this particular collapse, I would prefer that it come from an expert who is trained and experienced in this specific discipline. So far, I have not not read any replies from individuals who have made it clear that they are. That is the reason why I posted the question above.

I asked for

Quote:

...experience-based insight into the likely reasons for this particular collapse?
I would not expect someone who is unfamiliar with this type of bridge design to reply to my question, nor would I want them to. But if someone is experienced, trained, and qualified to provide the requested information, and they are inclined to do so, then it does not speak ill of them (or others) to formulate an appropriate reply. Each case is different, and a failure analysis must be performed to determine the specific reasons for the collapse. But if we followed the same line of reasoning that you provided in response to my question, very few engineering questions would ever receive replies on this website.

Maui

 

RE: Bridge Collapse in MN

Maui,

With all due respect, at this point all there can be is speculation even from experienced bridge designers until the forensic report is published.

I have some fatigue and fracture analysis experience for other structures.  What I don't understand is how bridge engineers can determine the life of a cracked structure using stress range approach.  Once you have a significant crack, the stress range approach is meaningless and fracture mechanics is necessary to determine an estimate of remaining life to failure.

David N Watson, P.E.
Drummond Company, Inc.
www.drummondco.com

RE: Bridge Collapse in MN

Evaluation of this bridge collapse should include bridge experts, the inspection team, as well as material experts, fatigue experts, those with knowledge of long-span truss design, geotech & foundations.  A diverse team such as that can avoid tunnel vision you get when you have a very specialized group who have seen the same details over and over and may not recognize possible faults.

Some of what is said above is useful, or at least insightful because it comes from a different point of view.  Notice how nearly all of the structurals zero in on the steel, while the civil guys seem to focus on the foundations. Besides isn't the point of this thread a collaboration of thoughts & evidence from engineers of all disciplines.  Offer up some helpful thoughts for the discussion.  

RE: Bridge Collapse in MN

darkwing - that is what i had hoped to point out among other things - it is too early for any sort of accurate speculation.     

Maui - one would have to have 'exact' experience in order to speak expertly on this matter.  I am not aware of any similar bridge collapses.

darkwing - back to fracture and fatigue mechanics in bridges.  Unlike the fracture and fatigue evaluations that GE or Honeywell or the DOD or Boeing or pressure vessel manufactures might undergo to determine the remaining life of a structure or element within a structure, once a bridge member cracks and is found and noted in an inspection, the crack is usually arrested via a arrestor hole drilled in.  It is further watched as are the surrounding members and or similar members.  

If the crack cannot be controlled by those means, the member or part thereof is typically replaced. The bridge industry does not engage in fracture studies as I point out may occur in other industries/companies.

That said, there are numerous bridge structures still performing well today with cracks and arrestor holes.  

Steelmover - there are many, many different areas that could have, in concert, acted to collapse the bridge.....I don't see the point in speculating about all of them.

Regards,
Qshake
pipe
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Bridge Collapse in MN

Lane closures usually create congestion in
the open lanes, also, should distribute
more load to some members than they were
designed for. I like to see if this has to
do anything with the failure.

RE: Bridge Collapse in MN

Darkwing and Qshake, I think that you may be reading more into my post than was intended. I understand that it is impossible to make a determination for the exact cause of this bridge collapse without a complete analysis of the appropriate forensic data by qualified experts. And it is simply too early in the process of the investigation for the experts who are currently working on this case to draw any conclusions themselves. I get it. So does everyone else here. But that isn't what I asked for. I requested insight into the likely reasons for the collapse, not for a detailed explanation of the specific cause of this particular failure. My objective was to get some objective feedback from a qualified, seasoned professional on the possible  mechanisms of failure that could have produced this result (examples include fatigue mechanisms, corrosion, overload, etc). Based on your replies, it would appear that you feel it is not possible or appropriate to do this at this point. I did not expect to receive a definitive answer.

Maui   

RE: Bridge Collapse in MN

Darkwing888 is absolutely correct.  If you review the 2001 report by Univ Mn., it points out that cracks had been observed in 1990.  As a "fix", holes were drilled at the end of the cracks to stop their propagation.  I could not examine the details of the "fix."
The questions that I had brought up earlier have not been answered.  Is there a report that evaluates the state of stress with a hole at the end of the crack?  A K1c calculation before and after the "fix" should have been made.

How many cracks and/or their density could exist before the margins of safety of the bridge is jepordized?

RE: Bridge Collapse in MN

Maui,
I think that there could be numerous reasons that could be listed here by bridge engineers on this site.  Just not likely reasons.  

Saying "likely" implies that there is knowlege available to rate each reason's probability.  I agree with Qshake that no one except those directly investigating the bridge can even come close to that "likely" position.

RE: Bridge Collapse in MN

I'm a new member, retired metallurgist. Two points for this thread .Some of those photos show distinct camera lens distortion so that things seem to be tilting when actually they are not !!....Vibrations - we got a new bridge here [Delaware River] and when they took down the old one last winter they chewed away the concrete support with jack hammer on excavator and at one point the entire truss hit resonant frequency !! Amasing to watch the frequency was about 2 cycles per second.Nothing subtle the whole truss vibrated ,loud,dust and dirt coming off the truss.I doubt that the roadway replacement would have caused that resonance !!

RE: Bridge Collapse in MN

The vibration/resonance idea is interesting. I believe it is important to remember that buildings and structures of most any shape/size can have many resonant frequencies. I once found that a rather large gymnasium had three acoustically resonant frequencies using a signal gererator, a rather large amplifier, and some voice of the theatre speakers.  I'm confident that more points of resonance could have been established had the school principle not shown up and dragged me outside by the scruff of the neck...
(Its amazing how much dust you can shake from the rafters with only a couple hundred watts)

RE: Bridge Collapse in MN

Fatigue, corrosion, resonance, footing failure, all things to consider.  But all I have to go on are some photos.  And the photos of the bearing and the main compressive web member show some brown staining which seem to indicate corrosion.  That steel member is carrying the entire load of the bridge, just as is the concrete pier.  And if reports that the bearing was locked are correct, that would bring bending of the strut into play.  For those who don't like speculation, apologies, but that vertical strut is where I would look first.  

RE: Bridge Collapse in MN

I'm not a bridge/structural expert, but suggest that people not get carried away with resonance schemes (the Tacoma Narrows 'Galloping Gertie' ca. 1940s makes a great visual on TV but very likely not relevant), as the New York Times article (bimr's link) notes "The most recent jackhammering of deteriorating concrete had occurred the day before, and none was performed the day of the accident, he said."

As to why it fell when it did, lots of corrosion issues and fatigue cracks, but as to the 'straw that broke the camel's back,' I have a hunch that the cement truck is mentioned in the final report.

RE: Bridge Collapse in MN

kenvlach, yes, there is a big difference between vibration and resonant vibration. The resonant type will tear things apart quickly....BTW the bridge here doesn't have expansion rollers .It was explained to me that the underside of the girder has a highly polished plate of stainless steel which then rests on the support which has a layer of teflon. Perhaps one of you bridge types can give details.Of the hundreds of photos I took I don't have one of that.We also have here a bridge , originally an a canal aqueduct, built by John Roebling in 1848 !!!

RE: Bridge Collapse in MN

2 year old photo of roller bearings:



RE: Bridge Collapse in MN

Its enough with all the bolt (rivits???) holes to scare me.  I don't suppose its seal welded either...? And it looks like paint is pretty expensive too.

http://virtualpipeline.spaces.msn.com

RE: Bridge Collapse in MN

May I ask is this type of doubled(?gusset?) plates a common feature in this type construction?

I'm with BigInch on this one it looks like this one hasn't been painted for a while if ever. I would hate to guess the millage on the last paint job. The coating appears to be similar to military lead based olive drab primer.
The rust spots could be where the inspector cleaned the area for testing, any bets.





RE: Bridge Collapse in MN

Double gusset plates are sometimes necessary to develop the strength of the connection.

RE: Bridge Collapse in MN

Picture of the southeast pier:

RE: Bridge Collapse in MN

The way this bridge fell... like a rock, not to mention the white-capped turbulent water from the lock, with the photographed pier tilting on the bank.... how is foundation scour not considered? What do we know about the piling beneath the foundations?

RE: Bridge Collapse in MN

The south piers near where the collapse started are not in the water or even close to the water so scour has probably already been ruled out. You can clearly see the bridge piers on the south end in this picture:



The forensic investigation seems to be focusing on the weights of the construction equipment and materials. It would be interesting to see the scale weight tickets for the trucks.

http://www.nytimes.com/2007/08/06/us/06collapse.html

RE: Bridge Collapse in MN

Asking again, Based on my observations of work on and the dismantling of some RR bridges/overpasses with very similar bearings/supports is it possible that one end of the bridge came completely off the bearing supports and resulting movement pull the other end off it's bearings. This is one way the bridge could have fallen as a unit.  

Several times I've seen where a RR crane would lift one end of an highway overpass and people would work on the bearing/supports.

In the 90's a friend got the contract to remove several RR/highway overpasses and his method was just pick it up and set it one the ground. They unbolted nothing, in fact getting the bearing off the support piers was lot bigger problem than taking down the overpass.

RE: Bridge Collapse in MN

I heard the head of the NTSB say that they were reviewing the records of temperature variations. This leads me to believe that they are studying the build up of member stresses in regard to the frozen bearing(s) that were discovered in 1996. This may have also lead to other failures as a result.

I also heard a statement that to replace a frozen bearing on this bridge that the entire bridge would have to be shut down. I am sure they were told to find another way to do it.

One thing that I know for sure is that alot of political pressure would come to bear to not shut down the busiest Interstate bridge in Minnesota. This may wind up being alot of finger pointing between the engineers and the politicians

RE: Bridge Collapse in MN

The MNDOT inspection reprot and the URS report don't describe the foundations. The MNDOT report did mention an underwater inspection in 2004 but no evidence of scour.

The URS report shows a scaled-down version of an original contract drawing of the elevation. Based on the drawing, the pier in the photo posted by bimr might be pile supported and the pier in the river (at the other end of the mainspan) looks like the footing could be resting on a tremie pour or caisson.

unclesyd - your theory might have possibilities. I saw a news flash that said the construction workers told investigators that the bridge was "wobbling" for several days. If by "wobbling" they meant an effect, for example, similar to the rocking of a table with on leg shorter than the others, that could point to a loss of a support, possibly at the south because that truss backspan is twisted whereas the other spans appear to have dropped straight down.

The first panel of each backspan is a 38' long cantilever that is also skewed. Skews do cause superstructure movements.


RE: Bridge Collapse in MN

I am reviewing the "Fatigue Evaluation and Fatigue Analysis" done by URS Corporation published July 2006.  One of the significant items is the behavior of the roller and rocker bearings. Below is a paragraph from this report.

"As a summary, the bearing measurement data indicates that the bridge expansion bearings are not functioning as designed.  There have been notations in previous bridge inspection reports referring to 'frozen' rocker bearings and corrosion and section loss at the truss roller bearings.  The erratic nature of the bearing measurements can be explained by the bearings components 'sticking' in place.  There is enough frictional resistance due to corrosion and debris to keep the bearing from moving until there is enough thermal force built up in the system to cause a drastic and quick movement of the bearing to relieve the force.  The bearings are not allowing the structure to move linearly with changes in the ambient temperature".

I would not be surprised if these "frozen" bearings were found to be a significant factor in the collapse.  Being one of the hottest days of the year with the bearings restraining longitudinal movement, a "quick movement" could have occurred to cause an existing crack (in one of the many fracture critical members that by definition has no redundancy) to reach critical crack length and complete member failure causing the bridge to collapse.

RE: Bridge Collapse in MN

For the bridge guys.
The construction equipment has been mentioned several times as a possible contributor to the failure. This is an 8 lane bridge and 4 lanes were shutdown for the construction. My question is similar to one of the above posts.

How many cement trucks equate to 2 lanes of bumper to bumber moving traffic?

Could one cement truck and one site mixer and 4 "Georgia Buggies" cause an eccentric loading.,either +/- when balanced against the traffic on the other side?

RE: Bridge Collapse in MN

bridgebuster: There are no cantilevers on Bridge 9340.  At Pier 8 on the North end there is a 38' overhang that is supported by a strut from the bearing on top of Pier 8.  At the South end there is a horizontal curve so the overhang is 35'-8" for the West truss and 40'-4" for the East truss.  Both of these are supported by a strut from the bearing on top of Pier 5.

RE: Bridge Collapse in MN

unclesyd:

I don't believe one concrete truck, one site mixer and buggies would even begin to come close to the design loads for that bridge. The sway frames between trusses would be designed for any unbalanced loads.

The frozen bearings and the resulting build up of thermal forces could have caused a truss member to fail, a connection to fail, the bearing anchorage to shear, the top of the pier to break off, the pier to tilt or the foundation to fail. The "wobbling" feeling that the workers describe only make me more suspicious of this type of failure. I only wish they had said something at that time!

RE: Bridge Collapse in MN

That was my feeling as to the loading at the time of the failure. 4 lanes, + a little extra, instead of 8 should equate to a half load +.

The mention of wobbling by the construction crew might have alerted someone, but wasn't someone for the WDOT overseeing the work. It just sounds all too familiar.

I have an ex-technician that use to work for our group and is now a bridge inspector for a large easter state. His qualificans are CWI, Level II MT, PT, RT with 25 years experiences. About a month ago while back home he and I were discussing his job. He said it is mostly paper work with very little actual inspection. He stated that one recent job he was on a hurry up/catch up inspection on a steel bridge that had fallen off the radar. He stated that at quitting time on day while they were in the steel work the whole crew heard a very loud bang. He stated that it was so loud that you could tell the direction. It was duly noted in daily notes and next morning when the supervisor was asked the commented that this is common occurrence and don't worry about it.
I just called him and asked for a little more information about the particular bridge. He said the type was listed as modified truss and had both bolts and rivets. They biggest problem the found was loose bolts and the normal paint problems. There had been some remedial work on the bridge. He also stated that it wasn't unusual for comment lines to be taken from the daily's.

RE: Bridge Collapse in MN

Here is the whole quote regarding the wobbling:

"Some workers said that the bridge had been wobbling unusually in the days before the collapse. With every layer of concrete that they removed, the bridge would wobble even more," the paper says, citing reports from Minneapolis police Sgt. Tim Hoeppner.


From this USA Today photo, it appears that two lanes had the deck surface partially removed for the entire length of the entire bridge.



It is too big of a coincidence that the construction was ongoing when the bridge collapsed. What about the effect of too much weight on a bridge deck with a surface that was partially removed?

RE: Bridge Collapse in MN

Just a WAG here... if the "wobbling" increased with each removed layer, could the weight of the concrete been a dampening force for any short-term catastrophic oscillations (rather than an overweight condition)?

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Bridge Collapse in MN

darkwing88 - look at Page 1-2 of the URS report, which shows the elevation of the bridge. I think we're having a terminology problem.

The first panel for each of the truss spans extends (or cantilevers)from the pier. (The diagonal member from the pier could be called a strut and the upper truss chord could be called a tie.) The far end of each  of these panels forms a hinge with the girder approach spans.

unclesyd - A loaded concrete truck is probably 32 to 36 tons.  Two lanes in each direction were closed and on some newscasts there was talk about the unbalanced traffic loading. I doubt that this caused the collapse. For example, if just the two outer lanes in one direction were fully loaded (assuming AASHTO lane load)there would be a LIVE LOAD uplift on the opposite truss. However, the dead load would counter the uplift.

From the aerial pictures it wasn't bumper-to-bumper trucks.

RE: Bridge Collapse in MN

jike: Currently doing substantial retrofit projects for heavy mining equipment, lifting a structure weighing 500 tons and carrying it 2 miles is a regular occurrence.  The total steel weight of Bridge 9340 is about 5000 tons.  Let's say the concrete also weighs 5000 tons.  That equals 10000 tons spread over 4 piers or 8 bearings.  So they would have to lift a maximum dead weight of about 1500 tons.  That doesn't seem to be excessive.  Bearing replacement should be easily done in a week with proper design and planning.

We return to the gutless bureaucrats and politics...

RE: Bridge Collapse in MN

It is possible that the construction on the bridge may have been the straw that broke the camel's back.

Perhaps the deck may have been carrying the build up of thermal stresses and when the deck was partially removed those stresses had to go somewhere (top chords of the trusses). Vibration may have also triggered the release of some of these built up thermal stresses.

This, of course, is all speculation and needs to be proven by the investigators.  

Does someone know if there was a horizontal truss between the top chords of the main carrying trusses?

RE: Bridge Collapse in MN

jike: The bridge as k-truss configuration between top chords.  I think they called them sway trusses in the URS report.

RE: Bridge Collapse in MN

Here are some Old Photos Of I-35W Bridge pfrom WCCO-TV showing the underside of the bridge:





RE: Bridge Collapse in MN

Sway trusses are in the vertical plane between the main trusses.

I was curious whether there were any truss members in the horizontal plane directly beneath the deck. It looks like there might be but then again my eyes might be fooling me.

RE: Bridge Collapse in MN

Off the main topic - The structural engineer used GTSTRUDL to model the bridge for the 2006 URS report.  Here are some of the things he did that I think is silly in this day and age: 1) he neglected the vertical slope of the bridge 2) neglected the horizontal curve of the North and South ends 3) cross slope of the structure was neglected.  Is GTSTRUDL that difficult to use to not model the bridge correctly?  I use STAAD and modeling those features would not be difficult at all.

RE: Bridge Collapse in MN

jike: yes the sway frames and portals above the piers are in the vertical plane.  I need to get a handle on the bridge terminology.

RE: Bridge Collapse in MN

Would the concrete bridge deck be the bracing element for the top flanges of the bridge framing?  If the cross section of the concrete deck was reduced, would that cause lateral buckling to occur?  From the photos, there does not appear to be a metal deck.  Seems like the sway trusses would prevent that, but since I'm not a bridge designer I don't know.

RE: Bridge Collapse in MN

in my previous post, I should have written... "If the cross section of the concrete deck was reduced, would that ALLOW lateral buckling of the trusses to occur?"

RE: Bridge Collapse in MN

The concrete deck is most probably the bracing element of the stringers (beams).

Whether it is the bracing element of the truss top chord, I am not sure. This why I ask the question whether there was any truss members in the horizontal plane just below the deck or stringers. For a bridge of this size, I would guess there is just so it could be erected safely and to maintain truss stability for deck replacement.

RE: Bridge Collapse in MN

My political rant: As a Libertarian, the government and all its departments are incompetent in many if not all areas of construction and engineering.  Political entities should not be building roads, bridges, maintaining roads or bridges but perhaps may be a source of funds for roads and bridges.  The government should do what only governments can do: police, defense, courts, etc. (a very short list for the etc.)  Early American bridge engineers had obtaining private funding as a first step in the design process.  The heads of DOTs answer to politicians.

RE: Bridge Collapse in MN

Go to Page 1-3 of the URS report it shows an elevation of the truss as well as the plan of the upper and lower laterals. The upper and lower laterals create the wind bracing system.

The roadway stringers sit on transverse trusses rather than floorbeams. The trusses were probably used for economy considering the large cantilever (in the transverse direction) of the roadway.  

Page 3-25 provides some description of the foundations.

I don't think neglecting the grade of the bridge in the analysis is a big deal; it's less than 1% over the length of the bridge (Page 4-13). The cross-slope of the deck doesn't need to be considered; both trusses are at the same elevation.

Is it OK to neglect the horizontal curvature? It looks as though it's within the AASHTO parameters. Should they have done so, hard to say? Particularly if the collapse was the result of a bearing failure at Pier 5. Skews always produce a racking force; without doing our own analysis we can't say what the effect would be in this case.


RE: Bridge Collapse in MN

RE: Bridge Collapse in MN


 
Land to the East of the bridge pulled East.

SOZT 8/2/2007
We have predicted that bridges crossing the Mississippi will be affected when the New Madrid and related fault lines adjust, going into the pole shift. Was this bridge collapse which crossed the Mississippi in Minnesota caused by such an adjustment, the footings on one side of the bridge moving in an opposite direction from the footings on the other side, or perhaps the bridge being pulled apart? The Mississippi River is born in Minnesota, tumbling out of the headwaters in the highlands of Minnesota over a series of natural falls. This is a clue that adjustments in the rock strata could be involved. The highlands of Minnesota come to a point at Minneapolis, with lower land lying to the East along this point. What caused the land to the East to drop, unless this land was stretched in the past? We have stated that the ripping apart of the St. Lawrence Seaway ends in the rumpled Black Hills of SD. Run a line from Montreal, at the mouth of the seaway, to Rapid City, SD and the line runs through Minneapolis. Why would an adjustment be made in the MIDDLE of this stretch zone while the seaway itself did not part? When we described the diagonal pull the N American continent is enduring, and just how this will snap when adjustments are made, we did not intend that this process would occur smoothly, all at once as described. Weak points along the rip lines give way one by one, each such adjustment placing stress on other points in a domino manner. The I35W bridge, being the larger of the bridges crossing the Mississippi at this point, was less able to adapt to a change in position vs-a-vs its footings on either side of the river, as it was an interstate bridge supporting several lanes, and thus had massive and thus rigid supports. Smaller bridges have more flexibility as they are built to withstand uneven loads on either end, thus are more springy by design. Will there be more such disasters along the Mississippi and in the cities that will be affected by the New Madrid and seaway rip? This is just the start, and when the pace picks up, there will be no question that something OTHER than Global Warming is the cause.
EOZT

Bridge collapse probe focuses on unexplained shift
Aug 3, 2007
http://www.cnn.com/2007/US/08/03/bridge.structure/

Investigators trying to figure out what caused Wednesday's massive bridge collapse are focusing on the southern end of the span, which "behaved differently" as it fell, the National Transportation Safety Board said Friday. The NTSB says one part of the bridge shifted 50 feet as it fell, while other sections collapsed in place. What's getting investigators' attention is the way the southern part of the bridge fell in a video they've already examined -- recorded by a security camera near the bridge's north end -- and the way the section settled after the collapse. It appears that it has shifted approximately 50 feet to the east and when we compare that to what we've seen in the rest of the bridge -- the rest of the bridge appears to have collapsed in place.

---------- Original Message ----------------------------------
From: "chriscon"<humvee@myway.com>
Reply-To: humvee@myway.com
Date: Fri, 3 Aug 2007 16:06:07 -0400 (EDT)

>

>Nancy: Was the collapse of the I-35 bridge across the Mississippi River in Minneapolis due to the land on the west end of the bridge moving NW in relation to the eastern end moving to the SE?
>
 
 

RE: Bridge Collapse in MN

humvee01 (Electrical), you are reading incomplete news stories:

NTSB says bridge shift wasn't cause of collapse
http://www.ydr.com/newsfull/ci_6546111

There was no "unexplained shift". After the collapse of the main span, the south approach deck tipped over in a secondary collapse like a house of cards, falling towards the west.

You would have to have an "unexplained shift" in the north south direction to pull the bridge off the supports and that did not happen.

RE: Bridge Collapse in MN

NTSB evaluating resurfacing project on I-35W bridge

When the bridge fell, a construction crew was replacing part of the bridge deck, transportation officials said.

Workers were shaving about 2 inches of concrete off 9-inch-thick slabs and replacing them with 2 fresh inches of concrete.

Workers were replacing all 9 inches in about eight parts of the bridge.

"In some parts, the 7 inches wasn't good enough quality," McFarlin said.

http://www.twincities.com/allheadlines/ci_6557477


http://www.chicagotribune.com/news/nationworld/chi-bridge_bdaug05,1,7333472.story

RE: Bridge Collapse in MN

unclesyd - those are steel deck bridges.  The MN bridge was a concrete deck.

RE: Bridge Collapse in MN

From the list I knew one was steel as having crossed it many times over a long span of time. It will still cause puckering of the seat covers.

Was the 35W bridge always a concrete deck design?

RE: Bridge Collapse in MN

There are a few issues which seem to be causing confusion.  For one, this bridge was not a steel arch, it was a three span steel truss bridge, roughly 266, 458, 266 ft in length.  The term "cantilever" does not accurately apply to the main spans, although the centre span may have been erected as cantilevers from each side.

By my reading, the fatigue cracking which was observed and addressed by drilling was in the approach girder sections, not in the truss spans.

The lateral load was apparently taken by a horizontal truss at deck level which spanned the full 990 ft.  Can anyone confirm this?  The problem with that is that the main supports at the river edge may have tried to take the lateral load without the capacity to do so, especially with the deteriorated state of the bearings and vertical web members above the concrete columns.

RE: Bridge Collapse in MN

darkwing88:

Perhaps the requirement to close down the bridge to replace bearings was a safety concern rather than a limition on capacity of the jacking mechanisms.

RE: Bridge Collapse in MN

unclesyd - I haven't heard anything about it being converted over from steel to concrete deck.  I honestly don't know its history in that regard...just that the photos show the concrete deck and that was what was being worked on at the time of collapse.

RE: Bridge Collapse in MN

The URS report was entitled "Fatigue Evaluation and Redundancy Analysis".  Skimming the (long) report, fatigue was discussed in great detail, but they did not actually find fatigue in the main trusses.  They seemed to concentrate only on tension members.  Compression members got little attention.  And the bearings were noted as not working, but that was not a focal point of the report.  Would be interested to know what the brief said URS was supposed to study.

The concrete deck was divided into a lot of sections by expansion joints, so don't think it was supposed to have a role in stability.

Don't know why some reports called it a steel deck bridge.

RE: Bridge Collapse in MN

"those are steel deck bridges" We need to start using commas again: steel, deck truss.

hokie66 - the lateral forces are taken by two horizontal trusses; one below the deck and the other at the bottom of the main trusses. The forces from the upper lateral system are transferred to the piers by a series of vertical trusses, called portals, installed between the main trusses.

RE: Bridge Collapse in MN

Unfortunately "deck" gets used in two different senses. One is what the cars drive on. The other is the relationship between the main girders or trusses and the load-carrying roadway. With deck spans the roadway (or railway) is supported on top of the steelwork.

Where the roadway goes between trusses or girders we call it a through bridge.

RE: Bridge Collapse in MN

Regarding civilperson's libertarian rant...

It is the bottom-line motivation of the private sector that leads to corner-cutting and shoddy construction such as the problems found with the Big Dig.  And every weird unbuildable bridge design I come across has come from a private consultant, not a state-employed designer.

Capitalism is not the One True Answer.  

Hg

Eng-Tips policies:  FAQ731-376: Eng-Tips.com Forum Policies

RE: Bridge Collapse in MN

There's a lot of truth to what HgTX says. Where I work, the company's list of qualifications needed to be a project manager (and we have various levels of PM's) does not make any mention of engineering or scientific skills.

The management thinks that being a PM boils down to watching budgets, meeting revenue targets, and keeping your staff entertained. Unfortunately, with all the corporate bureacracy we have to deal there's not enough time to deal with the engineering. Then they wonder why the company wide turnover rate exceeded 20% again.

RE: Bridge Collapse in MN

The problems with a capitalistically organized economy can be considered, so much so as to raise question about whether the beneficial aspects still outweigh the negatives.

Winston Churchill suggested that democracy is the worst form of political system--except for all the rest.

He might well have suggested the same for capitalism as a form of economic organization.

Capitalism may be the "least worst" of the alternatives available to societies.

RE: Bridge Collapse in MN

One lesson that may come out of this investigation for engineers is to stand your ground and don't be talked out of a correct technical decision by political pressure.

RE: Bridge Collapse in MN

I work in the bridge industry, first as a designer and now as a shop fabrication inspector/QA manager.  I am a licensed PE, a CWI and have passed the NBIS Bridge Inspection training.

I don't know what happened.

I have some theories as to what could have happened but I don't have access to the information necessary to figure it out.  I suspect it will take some time for the NTSB to find the critical initiation point.

I don't recall where, but I thought I saw a video of the bridge collapsing where it appeard the first span collapsed, then the middle span, and then the final span of the three span continuous steel deck truss bridge.

This causes me to believe there was a particular failure in the first span.  The collapse of the middle and final spans was very possibly caused as a chain reaction to the collapse of the first span.

I don't have the time to discuss all the mis-information I am hearing.  This is a technical subject, not unlike medicine or the law, which requires an individual to have a particular vocabulary.  However, for some reason, everyone thinks that engineering is earthy enough that everyone should understand what it is about, I guess because they can put their hand on the problem.  Any misunderstanding regarding engineering issues is frequently attributed to the engineer's inability to communicate.  I believe it is most often the lack of knowledge on the part of the audience that causes them to think they understand what they just do not.

I recommend we all just sit back and let the NTSB and the Minnesota bridge community figure out what initiated the failure.  The information will get to the proper authorities in due course.  -  Dinosaur

RE: Bridge Collapse in MN

We probably shouldn't discuss politics on this forum.  I think it will only hurt this valuable resource IMHO.

J

RE: Bridge Collapse in MN

Interesting that one would make the statement "I don't have the time to discuss all the mis-information I am hearing." and then proceed to state mis-information.

The statement "I don't recall where, but I thought I saw a video of the bridge collapsing where it appeard the first span collapsed, then the middle span, and then the final span of the three span continuous steel deck truss bridge." is incorrect.

Suggest that you red flag your post.

The collapse originated in the middle span and the collapse of the middle span triggered collapses in adjacent spans.

RE: Bridge Collapse in MN

Dinosaur:  There are a bunch of very experienced engineers here on this forum topic.  That's all I have to say.

RE: Bridge Collapse in MN

I don't think it's been definitively established that the main span (river span) went first.

The original drawings are now available from MN DOT. The south end could be the problem; the framing is a bit unusual.

Spans 3 through 5 are made up of continuous curved girders; the roadway is superelevated west to east (east being the high side.)

At the north end of Span 5 the girders frame into an end floorbeam at the beginning of the truss (Span 6). (At first glance the connection of the FB to truss (Sheet 19 of 94) is unusual. I have to look for more details) The roadway on Span 6 is also superelevated, transitioning to a normal crown at Pier 6/beginning of Span 7 (River Span).

All curved girder superstructure experiences uplift; the inner girders are the ones most affected.

enough said for now.




RE: Bridge Collapse in MN

jechols,

Maybe this forum is not the place to discuss politics, but if we had some engineers in politics rather than nothing but lawyers, I think our infrastructure would not be in such sad shape.

RE: Bridge Collapse in MN

"Minneapolis — NTSB Chairman Mark Rosenker put it plainly.

"We don't believe the southern portion of the bridge is where the accident began," he said Saturday afternoon."

 http://minnesota.publicradio.org/display/web/2007/08/05/ntsb/


"The south end of the bridge fell to the ground during the accident, but investigators have already determined that the stresses that caused the bridge collapse did not begin on the south end. The focus shifted over the weekend to the north and center bridge sections."

http://www.chicagotribune.com/news/nationworld/chi-070805ntsb,0,6826118.story

"Meanwhile, federal investigators trying to determine where the collapse began said that after closer examination, they had decided to shift their focus away from the south end of the bridge. That section shifted 81 feet during the collapse, but investigators now say they found no indications that was where the failure began."

http://www.boston.com/news/nation/articles/2007/08/05/crews_pull_car_out_of_river/

RE: Bridge Collapse in MN

Politics is involved in everything where a microphne is involved.

The dead giveaway is the phrase: "I wish to thank......".

RE: Bridge Collapse in MN

bimr - I saw that quote about shifting focus to the north end - but the video clearly showed the south end falling first...unless the video was pointing south and not north.

Other witnesses stated that they saw the south end go first.

The only way I can see the north end initiating the collapse is if it failed away from the central span somehow, pulling the south end off its support and causing it (the south end) to FALL first.

RE: Bridge Collapse in MN

JAE,

Agree with you. It seems that the collapse started in the vicinity of the Contractor's bulk cement semi-truck trailer close to the south end of the middle span. Once the middle span had fallen, the north and south spans then collapsed.

I was just responding to some of the recent posts above that have incorrect information and are outdated.

RE: Bridge Collapse in MN

bimr,

I don't know how a statement saying, "I don't know ..." followed by "... it appeared to me ..." is mis-information.  Are you saying it didn't appear to me that way?

darkwing88,

Several posters early in the thread stated they wanted to hear from someone with the right training/background what was really going on there.  For this reason I provided some of my credentials, not to inmply I know more than anyone else.  Then I followed with the statement that I don't know what exactly happened to initiate the failure.  This was intended to illustrate my view that unless you are on the ground you don't have access to the information to know exactly what happened, and I don't think the NTSB will have the information for some time to come.

I can't fathom how you two were offended by my post.

RE: Bridge Collapse in MN

Dinosaur, thank you for posting your original response.

Maui

RE: Bridge Collapse in MN

A website someone sent to me with lots of pics:

http://www.conphoto.net/collapse.html



If you "heard" it on the internet, it's guilty until proven innocent. - DCS

RE: Bridge Collapse in MN

Dinosaur:

Here is your statement;

"I don't recall where, but I thought I saw a video of the bridge collapsing where it appeard the first span collapsed, then the middle span, and then the final span of the three span continuous steel deck truss bridge."

The Corp of Engineers security camera video that was playing on CNN only shows the middle span and the north end span. It is impossible to see the south end span on the video because of the camera angle.

Unless you have another video, how could you possibly see something (the south end span collapsing) that is not on the video?

RE: Bridge Collapse in MN

The NY Times shouldn't have published that article; it's just going to cause a lot more confusion.

For instance:

"If there was a design error in the 1960s, failure to identify it before the bridge collapse indicates a problem with the federal inspection program, said Thomas M. Downs, who was the associate administrator of the Federal Highway Administration from 1978 to 1980. "

Either he was mis-quoted or expressed himself badly. Rouine bridge inspection does not include a review of design calculations.

RE: Bridge Collapse in MN

BridgeBuster, That's a very literal translation.  A bridge inspection might also be expected to verify to some extent that the design is holding up as intended.  A bridge inspection according to the methods used today may not measure actual stress levels, but maybe it should, is the message I receive.

http://virtualpipeline.spaces.msn.com

RE: Bridge Collapse in MN

Bridgebuster

A bridge inspection often includes a calculated load rating, based on observed section loss.  If the gusset plates were underdesigned, and then had some section loss, then an inspection could have picked up a rating deficiency.

RE: Bridge Collapse in MN

BigInch, jmiec,

I've performed several hundred bridge inspections, including several long-span trusses. Mr. Downs is mixing apples and oranges or perhaps he fails to see the difference between a Granny Smith and a MacIntosh.

Yes, an inspection is "to verify to some extent that the design is holding up as intended." However, when assessing components the criteria is "functioning as designed." The inspector isn't expected to give an assessment of the stress level in a main member.

Stress levels can be determined by strain gauge measurements but this is not part of a typical inspection; and it's costly.

"A bridge inspection often includes a calculated load rating, based on observed section loss.  If the gusset plates were underdesigned, and then had some section loss, then an inspection could have picked up a rating deficiency."

Not all inspections include load ratings; although they should if section loss is observed. Suppose the plates were underdesigned and had no section loss? An inspector wouldn't know there was a design deficiency, unless the plate  was glaringly thin when compared to a similar bridge. A load rating might uncover this deficiency. An underdesigned plate doesn't necessarily make the bridge unsafe: It reduces the design live load and the bridge would need to be posted accordingly.

There are two ratings: Inventory and Operating. Inventory is the maximum truck load that can be used for an indefinite period; Operating is the maximum permissible overload.

The thing with bridge inspection or building inspection, or any other structure is understanding how the structure is supposed to behave; how all the parts work together; what happens if one or more parts fail.

There are times when you look at something and know that it's wrong but there are plenty of times when the inspector will have now way of knowing  that the girder should have been 52" deep and not 48" deep.

RE: Bridge Collapse in MN

bridgebuster,

Quote:

I've performed several hundred bridge inspections...
I've performed part of a rehabilitation study for a bridge similar to 9340, so your experience far outweighs mine.  We did inventory and operating ratings for all the bridge components. Because our rehab included an inspection of the bridge, I was confusing an "inspection" with a "rehab study".  So you're right, an inspection would not necessarily include a rating analysis.

As you say, if there was no section loss, then there would be no reason to question the rating of the gussets.  I was merely trying to make sense of Mr. Downs remark.

RE: Bridge Collapse in MN

The level and placement of responsibility can get fuzzy for engineers doing inspections.

If I'm an owner and I have a failure of a structure I had an engineer "inspect" I'm having a hard time understanding why he would miss something so obvious that it would cause a failure - even if there was no "section loss".

This has been a sticky point for our firm in the past. Especially for buildings where the original drawings are not available and/or the original design intent is not clear.  

RE: Bridge Collapse in MN

unclesyd - you'd think those guys in Arizona would've learned something when a similar accident crushed a car in Colorado killing a family. After that happened, numerous DOT's were issuing new policies for steel girder erection. So much for policies.

Let's give Tom Peterson 20 stars.

RE: Bridge Collapse in MN

Looks like Mark Rosenker needs to learn how to say "no comment".  Giving the media tidbits from the NTSB serves no purpose.  If they want to print supposition, they can monitor this site.

RE: Bridge Collapse in MN

Below is the recommendations from the '06 URS report.  Does anyone know whether any of these recommendations were carried out?

RE: Bridge Collapse in MN

"Probe to See if Construction Played Role"

I would be willing to bet that a truck of some sort or a piece of equiptment "Fell through" a section of the bridge deck that was previously milled and was being prepped for re-surfacing. I read in a previous post that some portions of the bridge were undergoing a full depth deck replacement and other portions were undergoing partial depth deck replacement.
 Perhaps a truck drove over a portion of concrete that was not fully curred or a section that was milled and not capable of supporting the full weight of a piece of construction equiptment.
 You should be able to completly remove the deck from the superstructure without failure if the superstructure is stable.
 Overloading of the bridge with construction equiptment is a non issue in my opinion. The fact that there were loaders,tankers and trucks of different sorts on the bridge is minimal compaired to the normal traffic that crosses the bridge on a daily basis when all lanes are open.
  I dont think vibration from jackhammers would be an issue either. The DOT doesnt allow the use of large hammers on a bridge deck. If im not mistaken the max size allowable hammer is only about 17 lbs. vurses a 60 or 90 lb hammer which is much more destructive and the only reason for the smaller hammer is to lessen fractures in areas not to be re-surfaced.

A previous poster suggested that maybe formwork fell, striking a structural member thus collapsing it. I dont think so, 2x4's and plywood dont weigh that much or at least not enough to collapse a structure of this size unless the structure was in a state of total dis repair. Even if the formwork was filled with concrete, a 9" deep deck spread out over many sq ft dropping on an open girder structure would not cause too much damage. It would be different had it been a box girder type structure.

RE: Bridge Collapse in MN

darkwing,

It has been reported that the state selected the option of inspection only, but I don't see that option listed, unless NDE was interpreted as visual examination only.  There was apparently a lot of interpretation of this report by managers and politicians, with the objective of not doing anything.  And the report dealt with corrosion only in a peripheral manner.  The state's bridge inspectors wrote about corrosion, but again, nothing was done.

RE: Bridge Collapse in MN

My gut feeling screams at me to look to the foundation here being the ultimate cause of the failure - a shift/settlement, causing unanticipated stresses in a critical member in the trusswork.  The north abutment at the juncture of the main and approach spans to me is very suspect from the video sequencing I have seen.  Time will tell though.  I assume that the piers are on large caissons and not on deep raft footings.

I really feel for the pour souls who had a personal moment of H*** as they went down into the river, not being able to get out, or never realizing what happened.  Makes me realize how vitally important the work I do is, and how it impacts the lives of others. Note that the root word of vital is vita or "LIFE".  Life safety.   

Mike McCann
McCann Engineering

RE: Bridge Collapse in MN

UC-Berkeley's Hassan Astaneh doesn't cliam to know what caused the collapse of the bridge, and does not want to fault MnDOT for its failure. But he says from what observers know about the bridge, there were other warning signs.

At the time of the collapse, 18 construction workers from PCI were on the bridge. The National Transportation Safety Board is looking at the heavy equipment, including front-end loaders, the crew placed on the bridge. It's also asking about the weight, quantities of rock and other materials that sat on the bridge.

MnDOT spokesman Bob McFarlin said on that Wednesday, the crew was half finished with its job. It included resurfacing a few inches of the deck in some areas.

"In some areas of the bridge there was a complete concrete replacement, which means taking out the entire nine inches and replacing it with nine inches. And that was in eight spots along the bridge," said McFarlin.

Ripping off portions of the entire deck, professor Astaneh says, is playing with its structure. He says as a bridge weakens, the deck picks up some of the slack. It starts supporting the weight of the traffic and the bridge itself.

If a slab was removed over a fatigue crack or near an unnoticed crack, that could destabilize the bridge's delicate weight balance.

"That's not good news. That's another little storm coming in," said Astaneh. "So they're going to compound, and you're going to have all these little effects, which by themselves might not be critical to collapse the bridge."

Those little storms, as he calls them, include the heavy traffic of industrial trucks and daily commuters, the additional lanes that may have changed the balance of stress on the bridge, the fatigue cracks that were difficult to see, and the lack of structural redundancy. The bridge also faced environmental problems from water, ice and salt.

http://minnesota.publicradio.org/display/web/2007/08/06/bridgetroubles/

RE: Bridge Collapse in MN

The proportions in the photo of the gusset plates look a little odd to me. The plate does look a little thinner than I would expect. I am comparing it to the bolt spacing since I do not know what the member sizes are. Does anyone else feel this way?

Obviously, the analysis will prove this out one way or another.

The photo also looks like the plate might be bent like the bottom chord is not straight. Or could this be a distortion of the photograph?

RE: Bridge Collapse in MN

Quote:

"If you are a bridge engineer you should know," said Astaneh. "You should know that bridges built in the 1950s and '60s -- they use details that are not good for fatigue fractures. That means that this bridge is 'fracture critical.'"

Wrong.  At least they redefine "fracture critical" a little better a couple of paragraphs down.

Hg

Eng-Tips policies:  FAQ731-376: Eng-Tips.com Forum Policies

RE: Bridge Collapse in MN

"Meanwhile, a source close to the investigations said engineers are focusing on the thickness of the steel gusset plates, which he said were half as thick as they should have been. The source didn't know whether the original bridge design called for half-inch gusset plates or whether the contractor at the time used plates thinner than those specified.
"You cannot overplay the gusset design issue," the source said. "

http://www.twincities.com/ci_6577877?source=rss


RE: Bridge Collapse in MN

NTSB officials said "people have run maybe a little bit too far" with the statement on the gussets.

RE: Bridge Collapse in MN

from the Twincities article: "Gussets...are critical joints bearing a lot of stress... they were riveted and apparently welded to beams, both outdated technologies no longer used by bridge designers".

I didn't know we stopped using welding; nevertheless, a good article overall.

RE: Bridge Collapse in MN

The over 200 discussions presented thus far cover a great deal of points of view.  One of the questions I have, how do we learn from this experience?  And how do we apply this experience to other bridges having similar conditions?

It is my view that the two in-depth inspections should be used in conjunction with a calibrated analytical model of the bridge components to assess the "fracture critical state" of the bridge.  Included in this model should be an orthotropic deck.

From a detailed inspection, a map of the discrepencies can be developed.  Missing bolts, bearing conditions, cracks (location and length)and corrosion (location and extent) can be identified.  The effect of these discrepencies can then be introduced into the analytical model.  New fixity conditions can be determined for each affected structural member and included as adjustments of the model.  Then new critical load paths can be established.  Either a buckling or stress ( with K1, K2, and K3 fracture modes) criterion should be used as the final evaluation for integrity.

If there is no plan to incoporate the inspection results into an engineering assessment, then why inspect the bridge?  A critical assessment of the extent of a discrepency should be known, a priori, especially those bridges that have been designated as "non-redundant." If the standards of bridge design do not have specific recommendations as to fixes and the ramifications of these fixes on structural integrity, then what good are they?  

There have been studies performed by this author that shows that the life of a structure with small cracks can be exteded (almost doubled) by treating the tip of the crack.  By establishing a compressive zone immediately infront of the crack, one can arrest its growth.  I see no need to apply a 2 to 4 inch diameter holes as suggested by the standard.

RE: Bridge Collapse in MN

mtnengr -

Until a collapse mechanism(s)is found it is far too early to pass on learned knowledge from this tragedy.  All there is now are a few educated guesses from experienced bridge engineers and many wild ass guesses from laypeople.

Speaking from experience, wherein possible, cracks and other physical distress are modeled in a rating analysis of bridges.   This is not always the case though and is an area of improvement.

As for the standard of arrestor holes, this is viewed as the most effective means of crack extension mitigation.  I don't see how your proposal of introducing compression at the crack tip can be accomplished in many cases considering the geometry of the members and ensure that it is reliable once in place.  Clearly if it were reliable it would be a standard in use today.  It's not very practical.

Regards,
Qshake
pipe
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Bridge Collapse in MN

I'm not a bridge engineer, but it seems that the rating analysis of bridges may be part of the problem.  It doesn't seem that it really provides an analysis of the actual risk so that decision makers can factor that into the O&M decisions. A risk assessment procedure for rating bridges might be more useful.  This is often done with dams and could easily be done for bridges also. By constructing a dam or a bridge, you are creating a potential hazard if it fails. O&M of dams often involves risk assessments which looks at the probability of failure and the consequences of that failure.  This analysis of risk can guide dam owners and the public in the necessary maintenance, inspections and mitigation measures to take.  

Using the risk assessment example, if risk had been evaluated for this bridge, more proactive O&M might have been considered necessary.  Even using a qualitative assesment, the bridge would be considered high risk.  Probability of failure due to fatigue cracking, age, lack of redundancy, ship collision, etc. would have certainly been higher than normal.  And consequence of failure for this bridge are very high due to the high traffic volume, economic impacts, environmental impacts, loss of life and cost to replace.  A risk assessment would have likely shown this bridge to be at the high end of the risk spectrum as compared to other bridges in the state.  Perhaps a new model for evaluating bridges should be considered.

RE: Bridge Collapse in MN

cvg -

I agree that the actual rating analysis should be more quantitative providing a probability of failure, rather than a number which means it is more likely to collapse or not.  At the very least, all fracture critical structures should undergo this type of analysis.

Regards,
Qshake
pipe
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Bridge Collapse in MN

"Perhaps a new model for evaluating bridges should be considered."

Theoretically seems plausible, realistically, I don't know that it would help much.

DOT has a certain amount of funds available and subjectively allocates funds to repairs, maintenance, bridge widening, new bridges, etc.  Bridge widening and new bridges seem to be heavily favored by the public (spending money to repair a bridge isn't as noticeable to Joe Driver as a new bridge or bridges with more lanes).

This and other bridges are/were identified with problems.  There probably needs to be some statistical analysis to delineate when a particular rating factor an existing deficient bridge supersedes a factor for new / widening bridge project.

Maybe something like:

Project Priority Index (PPI) = Risk Factor x Demand Factor x Benefit Factor

            Bridge that collapsed    Some New Bridge
Risk Factor             9                       1
Demand Factor           2                       8
Benefit Factor          3                       4
PPI                     54                      32


Certainly crude, the gurus would have to work out the details probably with some weighting factors on each component of the formula.

I guess I'm basically agreeing with you, but just pointing out the public/political motivations for new / widenings have to influence the formula somehow.

RE: Bridge Collapse in MN

I'm going to get in trouble again, but here goes.

What in the hell ever happened to the find it and fix it philospohy when it come to a fabricated structure.

RE: Bridge Collapse in MN

unclesyd,

Glad to join you in trouble.  The inspectors found a host of things wrong with that bridge, but the managers, risk assessors, fuzzy thinkers, bean counters, politicians, etc. dithered.  And now they would like nothing better than to blame it on the long dead designers.  

RE: Bridge Collapse in MN

risk assessment was not popular with dams just a few decades ago either.  Than, due to several well publicized disasters such as the Teton Dam failure, federal legislation was enacted for dam safety.  But as you can see below, it took 10 years to implement and even then, only after the death of hundreds of people and billions of dollars in losses.  We are now going through the same process with levees after Katrina and perhaps (some) bridges should be treated in a similar manner...


Dam Safety History
1972 Failure of Buffalo Creek Dam, West Virginia; 125 deaths
1972 PL 92-367 the National Dam Inspection Act of 1972
1976 Teton Dam Failure; $1 Billion in losses and 14 deaths
1977 Kelly Barnes Dam Failure; 39 deaths
1978 Corps of Engineers begins the National Inspection Program
1979 Federal Guidelines for Dam Safety prepared
1979 Executive Order 12148 from President Carter created FEMA; FEMA Director to coordinate Federal Dam
Safety efforts
1979 Memorandum from President Carter requiring the head of each Federal dam safety agency to implement the
Federal Guidelines
1982 the National Program of Inspection of Non-Federal Dams completed and National Inventory updated by
USACE; Final Report to Congress

RE: Bridge Collapse in MN

note that risk does not equal the probability of failure.  Risk = failure x consequence.  therefore you can have two bridges with the same probability of failure which is high.  A large high hazard one and a small, two lane low hazard rural one.  Risk for the small bridge will be much lower since there are few consequences if it fails.  This makes it very simple for the lay person, even a politician to understand where the dollars should be spent.

RE: Bridge Collapse in MN

hokie66 & unclesyd,

There's not enough budget to fix everything that you find.  

You might be interested to look here:
http://www.fhwa.dot.gov/bridge/nbis/index.htm#10

Especially around question: Q313-18  

It still comes back to priorities.  It would be interesting to see where the DOT had the repairs slated in their long range plan.

RE: Bridge Collapse in MN

mjl23,
I agreed that the money needed to fix everything you find is not available as the monies have been spent in other places for other things. It just passed through the bridge fixing fund on the way to some bridge to nowhere.

Though I've never specifically be tasked with a bridge inspection I've assisted in the inspection of several large steel structures. One was a giant coal unloading gantry that was to be inspected as bolts were falling out and hitting the coal barges. As we were ascending the gantry for visual, MT, and PT testing it was evident that a major problem existed. Everywhere we looked there were major cracks and broken welds. I took the inspection crew down and conferred with the owner and much to his chagrin I told him that any inspection was useless and a waste of money was until he fixed the major problems. I offered to leave 2 technicians to mark all visible defects for repair. He opted out and and about three months later after another NDT company performed a thorough inspection and while waiting for an engineering evaluation a component of the gantry fell and severely injured two crewmen on a tug.

The moral of this tale is fix the obvious and mark the minor deficiencies for later. It appears to me that too much emphasis is put on finding the small fatigue cracks for study, evaluation, monitoring and ignoring the obvious like a warped gusset plate or a slightly bent member, etc.
Stop drilling a crack is just a band aid especially if you return and the crack and breached the stop hole.  

Another thing that bothers me is that the people responsible for the inspecting and repairs are investigating themselves.  





 

RE: Bridge Collapse in MN

cvg,

I don't know anything about how risk assessment of dams is done, but it seems to me that all the steps necessary to determine the risk of this bridge had been taken except to proceed to address the risk.  If the corrosion, fatigued members, and frozen bearings had been dealt with, we would not be having this conversation.

RE: Bridge Collapse in MN

Just a point of reference, the Seattle Space Needle was built for the 1962 International Exposition, and the support legs use gussets similar to the photos shown of those on the bridge, i.e., loaded with bolts, so that appears to be the standard practice of that era.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: Bridge Collapse in MN

Risk Assessment is starting to find its way into transportation facilities, but it's the result of 911. Right now, some agencies are using it as a tool to prevent a collapse resulting from a terrorist attack.

A few years ago I was involved in a tunnel design project and we did a RA for that reason. It is useful and forces everyone to think more deeply about various types of failures and their consequences.

AASHTO has developed guidelines for its implementation

RE: Bridge Collapse in MN

I agree that "Risk Assessment" has it's place in some designs but it should not be the controlling factor when possible fatalities are involved. Using RA there is major problem in that the first iteration is usually wrong and it takes several iterations to find some acceptable level of risks.
How would the number of permissible fatalities be determined say for a 10 car, 100 car, or a 1000 car bridge?

A prime example of RA failure is the tragic loss of the space shuttle Columbia with all it's crew. You might throw in the Challenger, though like bridges a little politics entered inot the picture.  NASA was the daddy of RA.

RE: Bridge Collapse in MN

Risk Assessment is a "subjective" process; and it's also a group process.

It's fairly simple to rank the importance of bridge components and understand the consequence of their failure.

Identifying the hazards (especially the non-structral) can be fuzzy, although there are consultants who specialize in this area.  

How much damage or potential loss of life is acceptable? It's a political decision. And the decision is somewhere between Dirty Harry ("Are you feeling lucky today?") and Josef Stalin ("If one man dies it's a tragedy; if a million die, it's a statistic.")

RE: Bridge Collapse in MN

NYSDOT instituted a Bridge Safety Assurance program nearly 20 years to identify and address various vulnerabilities such as seismic, scour, steel details, concrete details, collision and overload.

Each vulnerability is identified through a qualitative process. It's a very useful tool. The process helps to identify potential problems and prioritize where funds are best spent.

The following is a link to their website:

https://www.nysdot.gov/portal/page/portal/divisions/engineering/structures/bridge-program

It's not the same as the risk assessment concept, which is being used by some agencies to address terrorist threats.

RE: Bridge Collapse in MN

It seems there is some misunderstanding of the risk assessment process.  Risk assessment does not set an acceptable level of fatalities. And it really has little to do with terrorist threats.  Although, I am sure there are some risk assessments being done specifically for terrorist threats.  It merely calculates the risk of a structure.  Comparison of the risks for various bridges is a more logical way of making the decisions on priorities for bridge repair or replacement.  The methodology I am recommending is well summarized in the following links.

http://www.engineering.usu.edu/uwrl/www/faculty/DSB/Risk.html

http://www.engineering.usu.edu/uwrl/www/faculty/DSB/ANCOLDF.PDF

RE: Bridge Collapse in MN

From one of the papers referenced in cvg's post. He may not set the numbers but he certainly considers lives loss in an economic return on investment sense.

Quoting from Risk-Based Decision Making in Water Resources
Proceedings of 4th Conference/EF/WR Div./ASCE
Santa Barbara, CA/October 15-20, 1989

From a paper by David S. Bowles.

"The assessment of human safety can be presented as a histogram of probabilities of life loss events, or the cost-to-save-a-life. The latter should not be confused with placing a value on human life, which is entirely different. The cost-to-save-a-life is calculated as the cost by which a rehabilitation alternative exceeds its economic benefits expressed per life that would be expected to be saved by investing in the alternative. Thus, it can be considered as the cost of providing safety on a per-life-saved basis. Comparisons can be made with the cost-to-save-a-life that society is willing to pay in other areas involving involuntary risks, such as environmental risks, in order to judge acceptable levels of investment in public safety. It is also possible to calculate the expected number of lives that would be lost on an annual basis (similar to risk cost); however, this generally results in relatively small numbers, which are difficult to interpret. Other approaches to quantifying human safety are therefore considered to be preferable."

"The decision is especially sensitive and difficult where lives are at risk, or where large investments will be required to improve safety with little or no effect on project benefits, except of course to their expected longevity considering the reduced likelihood of dam failure."

I'll give him credit for one statement, "Risk Assessment procedures cannot be substituted for good engineering".









RE: Bridge Collapse in MN

"the cost-to-save-a-life that society is willing to pay "

Well, he is trying to simply look at the inverse of lives lost...i.e.  cost of lives saved.  That is a much more pleasant way of looking at it I'll admit.

But the other key phrase here is "comparison....with other areas of risk."

That is, or should be the main focus of any economic/risk evaluation.  That you have multiple ways to spend your money to mitigate risk in society or add to the general welfare.  

Raising millions of dollars in taxes to simply flood the bridge construction market will definitely save lives.  But perhaps more lives could be saved in many other ways for the same dollar.

RE: Bridge Collapse in MN

Even though they are of different designs and constructions there is commonality between the two failures.

The bearings froze.
The supports moved.
Problems with expansion joints.  

Chronology of 35W

Posted by prost
http://216.109.125.130/search/cache?ei=UTF-8&;p=rust+jacking+bridge+steel&amp;fr=slv8-
&u=www.startribune.com/462/story/1350056.html&;w=rust+jacking+bridge+bridges+steel&;d=aom6q-ljPRYH&icp=1&.intl=usad

Look at the Forensic Inspection Report for the Dunn Memorial Bridge Ramp Structural Failure on the following site.

Posted by bridgebusters
https://www.nysdot.gov/portal/page/portal/divisions/engineering/structures/manuals#engserv

RE: Bridge Collapse in MN

The Dunn Memorial Bridge Ramp is interesting .Going back to my earlier post  I'll ask again - can anyone give details of a new type of expansion system we have here on our new bridge ? A stainless steel plate on the girder resting on a teflon covered plate .

RE: Bridge Collapse in MN

Robertmet - which new bridge are you referring to?


The Roebling canal crossing you mentioned, is that the one in the vicinity of Lackawaxen PA?

RE: Bridge Collapse in MN

Purely conjecture by someone not versed in the art of bridge design and building.

Considering thermal expansion on a long span of this design (35W) what would happen if both ends were locked either at the bearings or the first expansion joints and one end was suddenly released, earthquake style?

If the ends were locked would thermal expansion cause the center of the arches to rise or would the expansion be taken up by elastic deformation of different members?

RE: Bridge Collapse in MN

If the expansion bearings were locked up, the thermal deformation of the bridge as a whole will be taken by elastic deformation in the piers.

Regards,
Qshake
pipe
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Bridge Collapse in MN

Bridgebuster, the Roebling bridge is one of three aquaducts he built on the Delaware and Hudson Canal.It crosses the Delaware at Lackawaxen PA. Four miles downstream is our new bridge at Barryville NY.I Googled  'bridge bearings ' and found www.bridgesite.com which has links to various makers of bridge bearings and expansion joints.Very interesting ,apparently these type of bridge bearings [polymer] are common now.

RE: Bridge Collapse in MN

I would surmise that there is not a design procedure for looking at a structure with frozen bearings as a standard load case. I would think, however, that this certainly would be looked at if frozen bearings were discovered in the field.

It is possible that the piers may deform to absorb some of the thermal movement, however, there may other undesirable affects that could lead to failure before all thermal forces afre absorbed

RE: Bridge Collapse in MN

To check the bridge members with seized bearings, you would just consider the ones that are seized as pinned supports rather than rollers.  This bridge had one pinned support, 3 rollers when built.  The rollers that are now seized would then have to be checked for the horizontal thrust, which might be difficult considering the advanced corroded state of the bearings.  Qshake may be right, that the thrust would be taken by bending of the piers, but only if the bearing is not the weak link.  

RE: Bridge Collapse in MN

I wonder if someone has an opinion as to how URS determined that there were 13x4=52 fracture critical members on the bridge, and they were all chord members.  The University report had previously identified some web members as critical.  Those tension diagonals in the first bay adjacent to the main piers look critical to me.

RE: Bridge Collapse in MN

Robertmet - elastomeric bearings are quite common now; long life; no maintenance; they don't lock-up.

hokie66 - to find the FCM's you remove a member, analyze the structure, see what happens; repeat the process for all tension members.

RE: Bridge Collapse in MN

bridgebuster - You'd be surprised how often and quickly a PTFE bearing can lock up.  

I've seen several examples of PTFE bearings locked up at the stainless steel/PTFE interface only to deform in shear the elastomer below.  In some cases the elastomer tore away from the sliding surfaces.

All it takes is for some debris to mar the surface of the PTFE. Or anything introduced that can raise the coefficient of friction from 0.02 (which is nothing) to 0.2 which could mean a lock up for the normal force on the bearing.

Regards,
Qshake
pipe
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Bridge Collapse in MN

Qshake - I was referring to a strictly elastomeric bearing not the pot type ones with PTFE. I've seen the problems you mentioned, including a bridge where the sliding surfaces were painted.

As they say, "if it moves, salute it; if not, paint it."

RE: Bridge Collapse in MN

Bridgebuster - ok.  I do recall that saying from back in the old barrack days!

Regards,
Qshake
pipe
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Bridge Collapse in MN

A writer to the Post-Dispatch this morning suggested that in the 60s, China was selling steel to the US; I can't vouch for the assertion by the writer, however my question is for the bridge builders--if there had been a new supply of steel (say even from a different US supplier than you have used in the past), would it have been standard operating procedure to test the steel once or even periodically for various parameters like hardness, to make certain the steel meets project specifications? Would there have been periodic testing to ensure continuing quality?

RE: Bridge Collapse in MN

DOTs have and use an extensive QA/QC process to verify the materials in their bridges.  As far as I am aware, they require fabrication shops to be certified by the AISC in order to be considered qualified to fabricate for bridges.  The AISC certification process further imposes requirements on their fabrication procedures and record keeping.

Steel supplied to DOTs for major structures is traceable back to the place it was melted into ingots.  It is tracked every step of the way to the bridge.  In the fab shops, each piece is marked to indicate its place in the bridge.  The shop drawings provide the information to locate which sheet of steel, or structural shape, the piece came from.

The tracking numbers are called heat numbers.  Each heat is tested for chemical composition and mechanical properties.  When required, additional tests such as hardness, charpy V-notch impact, etc. are performed and supplied to the fab shops and often forwarded to the DOT (owner).

Most of this QA/QC process is directly or indirectly mandated by the FHWA because of Federal Funding.  In addition, unless exceptions are granted, iron and steel products have to be made in America, start to finish.  I hear there are two significant projects overseas, one being fabricated in China for the State of California.  I do not know the "Buy American" status of that specific project.

Regarding the comment about bridge behavior with "frozen" bearings ...
In my area of the country, bridges are designed to withstand a seasonal temperature fluxuation of 120 degrees F.  Using the coefficient of expansion of steel, this corresponds to a temperature strain of 0.000780, half up and half down.  The problem can be considered as a prestress force analysis.  If you preload the steel with a strain of 0.000390 and release it, what happens?

In a determinant structure, it expands or contracts by this strain.  If it is indeterminant, multiply the strain by 29,000 ksi, and you get something near 11 ksi internal stress.  The structure will seek a new equilibrium and much of this load will cause additional force in the supports.  There will be some raising of the deck and some additional force in the piers.  The biggest problem is quantifying the degree of restraint at the supports.

RE: Bridge Collapse in MN

Dinosaur - your comments are appropriate for the state of the steel fabrication industry now, but in 1960 which is PROST's point, I know that AISC didn't certify fab shops and most states didn't have a "buy America" policy either.

Regards,
Qshake
pipe
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Bridge Collapse in MN

Yes, I'm sorry I was interrupted while writing that long post and lost my train of thought.  I had meant to mention the disaster in 1967 that caused many of these policies to be enacted.  However, I believe steel was still tracked by heat number even before the Silver Bridge collapse.  Many welding and materials policies were upgraded after that.  Hopefully a similar process improvement can be obtained from this accident, but I would be surprised if we learned as much this time around.  We still build non-redundant fracture critical steel structures and install pin-and-hangers in new construction.  Sometimes I feel I am beating my head against a wall.

RE: Bridge Collapse in MN

Perhaps there could have been Chinese steel in the bridge. In high school, we spent a full term studying Russia and China; I recall a lecture about the Chinse steel industry in the 50's & 60's: Complete disaster.

At the time this bridge was built US Steel and Bethlehem were still the major players in the US.

RE: Bridge Collapse in MN

The only imported steel in any volume at that time was the Japanese steel and I do not think the volume was that great, much of that was on the west coast.

When I worked on a U.S. Steel plant under construction in Minnesota in 1966, the main concern was grinding the "Bethlehem" off some steel from the local fabricator when he let it get by on change order fabrications.

Dick

RE: Bridge Collapse in MN

There are many problems with steel today because the demand is so high.Mills in China and India are sometimes selling  one type of steel for another [200 for 300 stainless].Even inventing new grades [ 200 stainless].Out of spec steel. Steel with high amounts of trace elements. Best to deal only with reliable mills, demand documentation [chemistry, mechanical properties etc] even though more expensive !!

RE: Bridge Collapse in MN

concretemasonry got it very close to right as both Bethlehem and USS both embossed there names on what they produced. Each mill had a slightly different marking. There was no particular effort to keep track of the material as specific heat numbers but there were run numbers that with a little effort one could get the actual chemistry and physicals of a run. During the Korean War a lot of steel shapes came from Europe.  

The actual tracking of a particular heat of metal didn't gain momentum until Adm Hyman Rickhover required all materials used in the construction of Submarines be tracked. He came down hard on all of metal producers that supplied materials for the Navy. It was quite helpful as the metals industry went across the board. The biggest change was in welding consumables as you didn''t have to remember the color codes and wander why one batch performed better than another.

The Nashville Bridge Plant near by boyhood home always slipped some paint on the embossed name on the steel used in fabrication so it was quite visible when loaded on a rail car for shipment. At this plant it was TCI, the Tennessee Coal and Iron Co.

My brother has talked to one of the old fabricators that work in the Nashville Bridge Shop. They made components for steel bridges all over the country. The components they made were 99% hot riveted. All holes were drilled and reamed and if at all possible machine set using tools by Mesta. They only hole punching occurred during WWII for what he called light weight construction. All the connection holes were drilled and ream whether they were for bolts or rivets.
He commented that when the machine setters hit the rivets there was no problem with the rivet being tight. They only used American Steel.
   
Sidelight:

The Nashville Bridge site is being razed to build a modern  DI pipe mill. If it hasn't been removed there is onsite a block of Zinc that is 6' wide x 8' deep x 110' long form the old galvanizing plant. Removing it is going to be chore as it contains about 2% lead.

 

RE: Bridge Collapse in MN

In the last 20 years, we've used a lot of imported plate and domestic plate, and haven't seen a great deal of difference in quality- if anything, more problems with the domestic.  Don't think we've seen much if any from China.

Last time I heard, several years ago, out of the ten largest steel mills in the world, none were in the US.

Regardless, if you build a structure and it operates fine for 40 years and then collapses under minimal load, that's not the kind of problem you'd normally associate with substandard materials.

RE: Bridge Collapse in MN

Isn't it the rule to procure all structural steel locally? Only 1% of steel can be imported?

RE: Bridge Collapse in MN

Haven't read much of the tread.

My guess, because if you're not guessing, you're not playing along:  

The compromise was with a connection from the secondary truss to the top chord of the main truss on the South and East side.  The connection was corroded or fatigued or both; it was bad and the top chord of the truss that was supposed to be braced by the secondary truss was now only being braced by the decking.  Contractor comes along to replace the decking, knowing what all contractors and bridge engineers know, that you can remove the decking because the bracing is provided by the structure...  The top chord on the east (at the south end) buckles, splitting the deck first at the middle of the lanes and then pulling the entire south end to the east.  From there the bridge collapses south to north.

Like I said guessing...
  

RE: Bridge Collapse in MN

Here is some additional information on bridges from another source:

Source: American Road and Transportation Builders Association
In view of extensive coverage following the Interstate 35-West steel bridge collapse in Minnesota, ARTBA released key highway and bridge statistics:
Of the 594,709 U.S. bridges, 152,945 (26 percent) are structurally deficient or functionally obsolete, according to 2006 Federal Highway Administration data. Of the 961,382 federal-aid road miles, 161,750 (17 percent) are reported to have conditions needing resurfacing or reconstruction.
Of Minnesota's 13,008 bridges, 1,586 (12.2 percent) are structurally deficient or functionally obsolete -- third-lowest in the nation, according to FHWA. Of Minnesota's 31,612 federal-aid road miles, 2,871 miles ( 9.1 percent) are reported to have conditions needing resurfacing or reconstruction.
According to the U.S. Department of Transportation's 2006 "Status of the Nation's Highways, Bridges, and Transit: Conditions & Performance" report: a) Structurally deficient means that significant load-carrying elements of the bridge are found to be in poor or worse condition due to deterioration and/or damage; or, the adequacy of the waterway opening provided by the bridge is determined to be extremely insufficient to the point of causing intolerable traffic interruptions. A deficient bridge, when left open to traffic, typically requires significant maintenance and repair to remain and service. And, b) Functionally obsolete bridges result from changes in traffic demand on the structure. For example, a bridge designed in the 1930s would have shoulder widths in conformance with the design standards of the 1930s. However, design standards may have changed since that time.

Not too technical, but another description of the terms being tossed around.

Dick

RE: Bridge Collapse in MN

The video actually seems to indicate a main truss member or joint failure at the north end since it drops prior to the south end. Rotation, and lateral displacement could be caused if one main truss failed prior to the opposite main truss. I think in the end they will determine that one main truss joint failed, and lead to progressive collapse. I'm not a bridge engineer, but have designed some long spanned steel trusses.

RE: Bridge Collapse in MN

I know this is a bit off topic, although Concretemasonry’s post made me think. Who is actually reviewing these bridges and roads? If it is a professional engineer reviewing a  bridge that is “structurally deficient” don’t we as structural engineers have an obligation per our ethics to be sure that something is done about it. I have to wonder if I found a structure that was “structurally deficient” and only stated that it was structurally deficient in a report and it fell down and killed somebody, as a professional engineer where would I be in terms of adhering to my engineering ethics?

RE: Bridge Collapse in MN

Movie frames of the bridge collapse:

http://www.twincities.com//ci_6595490?IADID=Search-www.twincities.com-www.twincities.com

A source familiar with the investigation has told the Pioneer Press that investigators were looking at the possibility at least several plates, known as gussets, were too thin at half an inch. Just inside the piers lie four gussets labeled "U10." They're a half-inch thick, according to design records.

RE: Bridge Collapse in MN

bimr,

The video definiately shows that the failure occured near the south pier.  The bottom chords near the north pier failed after the collapse, I think due to excessive rotation of the members during the fall. thereafter,the north approach collasped, I think due to excessive elongation of the top choars near the south pier. I also think, that the east and west side bottom chords near the north pier did not deform simultaneously, which may cause the entire span to rotate westward during fall.  This is probably why the span was about 50' away from the south pier after the fall.

I truely believe that something went wrong near the south pier bearing.

RE: Bridge Collapse in MN

It will be hard to fault the original design as it picked up two additional lanes of traffic.

Copied from ENR

"Engineers Swarm on US Bridges to Check for Flaws."

By Tom Ichniowski and Thomas F. Armistead, with Tom Sawyer, Jonathan Barnes, Bruce Buckley and Lucy Bodilly

"Meanwhile, in Minnesota, planners pushed ahead to have a replacement bridge constructed rapidly, although they quickly ran into conflicts over potential enhancements such as adding light rail and more lanes. The Minnesota Dept. of Transportation on Aug. 14 whipped out a preliminary design to solicit feedback. It features a 10-lane bridge with four shoulders, allowing room for expansion. The old bridge started as a six-lane crossing and later was expanded to eight by claiming most of the shoulders. The proposed alignment appears to match the old one."

RE: Bridge Collapse in MN

I concur with imnotclever's guessings above.
Also adding that the wobbling experienced by the workers, that was increasing as the work (removal of concrete deck) proceeded, cannot be explained by the failure of some gusset plates, unless this failure occurred many days before the collapse. The wobbling should be caused by the buckling of a main element, that, till the collapse, was stopped and recovered by the intervention of some other structural restraint.

prex
http://www.xcalcs.com : Online tools for structural design
http://www.megamag.it : Magnetic brakes for fun rides
http://www.levitans.com : Air bearing pads

RE: Bridge Collapse in MN

Wobbling - somewhere I read that all of the workers had been interviewed and none of them experienced anything abnormal [such as wobbling] before collapse !!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources