Possible design flaw found in collapsed U.S. bridge

http://news.scotsman.com/latest.cfm?id=1247802007 ^

[traumer]

MINNEAPOLIS (Reuters) - A week after a deadly bridge collapse, U.S. Navy divers cut through tangled debris with underwater torches and saws on Wednesday in the search for victims while investigators identified a possible flaw in the 40-year-old span's design.

The August 1 rush-hour collapse of the Interstate 35W bridge hurled vehicles into the Mississippi River 65 feet (20 meters) below, with many tumbling onto the bridge's crumpled concrete deck.

Reacting to the disaster, officials demanded inspections of potentially suspect bridges across the United States amid renewed calls to shore up the country's aging infrastructure.

Five people were killed in the bridge collapse, a death toll that was confirmed within a day of incident. Eight other probable victims are listed as missing.

The recovery process has been slowed by huge slabs of steel-reinforced concrete and dangerous chunks of debris submerged in the river's swift, turbid waters. In some cases, divers had to use their fingertips to read license plates.

"This is going to be a process of having to, most likely, pull these vehicles out and do a long-term extraction, taking apart the vehicle to recover evidence, (and) any (human) remains," Minneapolis Police Capt. Mike Martin told reporters.

National Transportation Safety Board investigators said they had found a potential design problem with gusset plates, or steel plates that tie together angled steel beams of the bridge's frame.

Investigators are trying to verify loads and stresses on these plates at specific locations as well as the materials used to construct them.

Officials stressed the finding is preliminary and would not say exactly where the plates were located or whether failure would have caused the collapse.

"We are continuing to make progress on this investigation, and each area of inquiry gets us closer to ultimately determining the cause of this tragedy," National Transportation Safety Board Chairman Mark Rosenker said in a statement.

Out of some 100 people injured, only a handful remained in hospitals with one in critical condition.

City officials have called the large number of survivors miraculous.

For the families of the missing it has been an agonizing wait. Members of Minneapolis' large Somali immigrant community are grieving over the presumed death of a 23-year-old nursing student, who was pregnant, and her 2-year-old daughter.

Minnesota officials were quickly laying the groundwork for replacing the vital eight-lane bridge, which had been the state's busiest with 140,000 vehicles crossing it each day.

Construction bids were due on Wednesday and officials hoped to choose a contractor within weeks to build a new bridge by the end of 2008, with the help of $250 million (123 million pounds) promised by the federal government. One proposal called for two spans of five traffic lanes each, with room for light rail or buses.

It was unlikely a new bridge could be completed before the Republican Party convention in September 2008, to be held in neighbouring St. Paul.

[ConservaTexan]

I didn’t know Bush was designing bridges 40 years ago.

[Perdogg]

Maybe Halliburton will get the job.

[traumer]

Was Bush in college at that time ?

[Perdogg]

My guess is, it met code 40 years ago.

[DoughtyOne]

Liar! Heh heh heh... just kidding. I expect that will be the charge on DU.

[calex59]

I didn’t know Bush was designing bridges 40 years ago.

If the sun went nova, in the time it took for the explosion to reach us and wipe out the earth, some liberal would blame Bush for it!

[Doctor Raoul]

Design flaw. We should all write a Letter To The Editor and stick it up the bum of the Bush Derangement Syndrome sufferers.

[DoughtyOne]

What is strance about this is that traffic had been reduced in both directions if reports I heard are true. One would think the load was probably 1/2 what it normally was. Why would it fail now if these plates were the issue?

[hosepipe]

[.. Possible design flaw found in collapsed U.S. bridge ..]

NOW thats funny..

[ButThreeLeftsDo]

Thanks for posting this.

I’ve added the Keyword “35w”.

Please add this to keywords on any threads about this tragedy so everyone can more easily track new developments.

Thanks.....

[umgud]

Of course there’s a design flaw. While we don’t know what initiated the collapse, we do know that because of the design, the whole bridge came down. A proper design wouldn’t have the whole thing coming down when just one section has failed.

[Westbrook]

> I didn’t know Bush was designing bridges 40 years ago.

Doesn’t matter.

It’s STILL his fault for spending all that money in iraq when he could have spent it building new bridges and fixing old ones.
/SARC

Of course, we NEVER hear about the over one TRILLION dollars spent by the US Dept of Education, and how that money could have been better spent building new bridges and fixing old ones.

And since the establishment of the Dept. of Education by President James Earl Carter in 1977, what aspect of American education has improved? Even a teeney, weeney, little bit?

What have we gotten for our TRILLION dollars, besides another bloated government bureaucracy?

[Proud_USA_Republican]

Even though this bridge was designed and built 40 years ago, if Hillary was president, this never would of happened...............

[Hurricane Bruiser]

Many bridges relies upon all sections for support but you are correct that there obviously was a design flaw. Perhaps the workers removed a portion that was in some way supporting the bridge structure.

[metmom]

Good question, but conspiracy theories (about terrorism) will only get you flamed from some quarters.

[Jeff Chandler]

Why would it fail now if these plates were the issue?

One Freeper tied it to the obesity crisis.

[Last Dakotan]

Why would it fail now if these plates were the issue?

A fatigue crack can move through material very slowly, even over a period of years. The final failure through the overloaded remaining material can happen at any load.

I've seen fatigue cracks that leave only 5% of the original material remaining before a rapid final break.

[TXnMA]

The two photos in this post from the live thread at http://www.freerepublic.com/focus/f-news/1874950/posts?page=1659#1659 show what might be construed as a "failed gusset plate".

In the top photo, it is at the right side, on the big horizontal beam. In the bottom photo, it is on the left.

Notice the holes where rivets have pulled out -- and how the plate is buckled.

These photos show the area around the mainspan piers on the south shore where the structure failed laterally, (It toppled to the east) whereas all of the other failed slabs dropped (approximately) straight down.

Many believe this area to be that where the initial failure started...

[Ronzo]

National Transportation Safety Board investigators said they had found a potential design problem with gusset plates, or steel plates that tie together angled steel beams of the bridge's frame.

Investigators are trying to verify loads and stresses on these plates at specific locations as well as the materials used to construct them.

Officials stressed the finding is preliminary and would not say exactly where the plates were located or whether failure would have caused the collapse.

Here is a picture I found on Flickr showing the collapse from ground level...in the left hand side of the frame you can see one of the "gusset plates." Notice how it crumpled just a bit. I don't think this particular plate caused the collapse. Most that I've seen in pictures seemed to have held up just fine...but the ones that failed are probably burried under all that concrete roadway.

[Mygirlsmom]

Don't you know Karl Rove has a time machine? He keeps it right next to the weather-controller. Yeah, he and the Pres went back in time 40 years, messed with the design for this bridge and returned undetected.

Or so they thought......

[hercuroc]

http://img.photobucket.com/albums/v210/hercuroc/gore.jpg

I’m waiting for the inevitable global warming cause for this accident.
ice caps melting causing higher tides at full moon pushing on bridge supports...yadda,yadda

[Ramius]

Of course there?s a design flaw. While we don?t know what initiated the collapse, we do know that because of the design, the whole bridge came down. A proper design wouldn?t have the whole thing coming down when just one section has failed.

Sorry, but it's not "of course" there is a design flaw. In fact the more likely culprit will be about maintenance than design. This bridge stood for 40 years under far greater loads than were present when it fell. That doesn't imply a design weakness at all.

With regard to a single failure bringing down the whole bridge this is almost to be assumed with such structures. Bridges stand because they divide, spread and balance enormous forces. A break anywhere in the structure will almost always bring the entire thing down.

It could turn out to be any number of things. Most likely a combination of things. But the place to look first will be all about metallurgy and maintenance.

[BurbankKarl]

truss uplift?

[Finalapproach29er]

It did; the code changed the next year (1968).

[umgud]

Sorry, but it's not "of course" there is a design flaw.

I didn't say a design flaw brought it down. I have no idea what did initiate the collapse and even said so. I implied it was a poor design for the whole thing to come down because of a failure in one section. This isn't a suspension bridge. The adjacent bridge has a much better design. The Oakland bay bridge suffered heavy damage in the '89 quake and one section failed and dumped cars into the bay, but the whole bridge did not collapse due to the failure of the one section.

[9422WMR]

Oh this is such BS.
Did you not see the before pics and reports that indicate the DOT was storing road base and construction material ON THE BRIDGE prior to collapse?
The bridge was IN USE, under construction?????

[SunkenCiv]

Didn’t Al Gore invent bridges?

[Ramius]

Think of a stone arch. Pull one stone and the whole arch fails.

In a truss bridge a failure of any segment likewise will compromise the entire structure.

The sections that fell in the bay bridge were just that. Sections of roadbed that broke. There is no parallel to this bridge.

[RGSpincich]

Nine popped/broken and missing rivets. No tears in the holes on the gussett or framing. Rust/corrosion is my guess.

[umgud]

Sections of roadbed that broke

Good point.

[ROTB]

Tancredo said he would end it.

[Rudder]

I didn’t know Bush was designing bridges 40 years ago.

No, fully certified mechanical engineers did this and apparently they don't know what Shinola is.

[Finalapproach29er]

No, I’d didn’t see or hear such a thing.

[FlingWingFlyer]

The real miracle here is how this "flawed" bridge managed to elude the sharp eyes of the Clinton administration for 8 years without Clinton and his band of sharp-eyed bridge checkers dicovering its flaws. Wow!

Extreme sarcasm/off

[Mad_Tom_Rackham]

What is strange about this is that traffic had been reduced in both directions if reports I heard are true. One would think the load was probably 1/2 what it normally was. Why would it fail now if these plates were the issue?

Due to Bush's terrible economy and Bush's high gas prices, only 1/2 of the normal traffic was necessary for the bridge to fail, because Bush's Global Warming had already weakened the plates, and they failed, even before Al Queda could blow them up because Bush didn't catch them due to Bush's quagmire in Iraq.

[AngelesCrestHighway]

Were our bridge designs outsourced to Mexico 40 years ago?

[SAJ]

Hey, Tom, that's not bad!

Just with an offhand post, you make more sense than the moonbats (granted, that's like shooting a tuna fish in barrel, but even so...).

FReegards!

[DoughtyOne]

I know, but my comments weren’t meant to imply anything like that. Just pondering...

[DoughtyOne]

I hadn’t thought of that. Thanks for the oversized information. LOL

[DoughtyOne]

Thanks for the comment.

To my way of thinking the vibrations resulting from the repairs may have contributed, but then it would seem your average traffic would cause vibrations also.

Along those lines, harmonics is an interesting field. Perhaps the jackhammer or whatever hit just the pace to cause the worst damage for the failed part.

Take care.

[Lancey Howard]

Construction bids were due on Wednesday and officials hoped to choose a contractor within weeks to build a new bridge by the end of 2008, with the help of $250 million (123 million pounds) promised by the federal government. One proposal called for two spans of five traffic lanes each, with room for light rail or buses.

Wait until the EPA gets involved. If you think that's a joke, ask homeowners in Ocean City, NJ about their bridge rebuilding project.

[DoughtyOne]

I get pretty angry with Bush, but I do find a lot of humor in the stupidity of the left, that is just as likely as not to pick up on your post and adopt the talking points.

Thanks Mad_Tom...

[KAUAIBOUND]

I am a structural engineer with 28 years experience and you are 100% correct. The contractor overloaded the bridge with construction material. The NYT slant attempting to create fear over the use of gusset plates is IMO a deliberate attempt to create fear in the general (and generally uninformed) public and cause an outcry about spending money on the WOT. It’s all about Bush.

I haven’t seen any drawings or diagrams of the bridge, but I suspect that the reason that failure of one part of the bridge caused the failure of the entire bridge was because the bridge was designed as a continuous span structure, unlike the Oakland bridge that collapsed in the 1989 earthquake, which was a single span bridge. Continuous span bridges permit longer spans and more economical used of material, but are susceptible to progressive failures such as occured.

[jeffers]

That gusset appears to have failed due to a moment. The far end of the member attached at that point was rotated about that gusset connection point, popped the bolts and pulled free.

A "possible gusset design flaw" is not much to go on. Much more useful would be the location of that gusset or gussets, as we still don't have the major components of the failure sequence in proper order yet.

Still focusing on the north end of span 5/pier 5, and/or pier six and the superstructure above pier 6 here. Both still look viable. Initial failure could have been anywhere from the midspan of span 5 through the south half of span 7 (center span), probably nearer the east side than the west.

The most interesting point on the bridge for me right now is just north of pier 6, east truss. Road deck south of pier 6, and presumably the span 6 east truss look prety good comparatively, but the span 7 east truss got hammered hard just north of pier 6.

I've isolated the SE kingpost (buckled under load) and the top chord, (folded down under moment at north end of span 6 road deck) and one other member, either a tension brace or the bottom chord, but that panel is so scattered that it's hard to piece it back together.



Blue arrow 1 indicates the SE kingpost, blue 2 is probably the tension brace angling north and down from the top of the SE kingpost, blue 3 is probably the east truss span 7 top chord, and blue 4 is probably the span 7 east truss bottom chord, although it may also be the diagonal tension brace if blue 2 is wrong.

Red arrows 1 and 2 seem to indicate that the top of the southwest kingpost rotated south, both bottom chords are bent consistent with this theory. So is the top chord of the pier 7 west truss, just slightly off the end of blue arrow 4.

Red arrow three indicates similar behavior of the span 7 east truss top chord.

If the center span broke free early on, its counterweight would be deprived to span 6 just south of pier 6, and would explain why the road deck was so compromised just north of pier 6.

However, the SE kingpost or other members closely associated with that panel of the east truss could easily have failed first, dropped the south end of the span 7 east truss, overloaded the south end of the span 7 west truss, and accomplished the same result.

I'm starting to consider a failure around the second or third panel of the east span seven truss, just north of the SE kingpost. That would be at the right end of the member marked with blue arrow 3. Supporting this is the position of the east truss span 7 bottom chord (blue arrow 4.), which does not appear to have leaned over eastward with the rest of the eastern truss at pier 6.

Initiating trigger or not, bad things happened there.

[jeffers]

Yes, the more i think about this, the more sense it makes. It resolves an issue that’s been bothering me since I first realized the trusses leaned east at pier 6.

THE SPAN 7 ROAD DECK DID NOT LEAN EAST WITH THE PIER 6 TRUSS PANELS. IT DROPPED STRAIGHT DOWN.

Since the trusses above pier 6 clearly leaned east, and since they did so without taking the south end of span 7 with them, span 7 MUST have seperated from BOTH main truss kingpost panels, PRIOR TO those panels leaning east.

It explains why the SW kingpost rotated, and why span 6 failed, it lost its center span cantilever counterweight.

The critical evidence is in the river, close to the south shore.

[jeffers]

Still doesn’t resolve the basic question though, whether span five dropped first, or something near pier 6 failed first.

With the cantilevers in play, I can build a good case either way.

Still, another brick in the pile of understanding.

I can now be reasonably certain that span 7 seperated from the pier 6 kingposts before those kingposts started leaning east.

Not the whole answer, but better than a poke in the eye.

[metmom]

Along those lines, harmonics is an interesting field.

That's an interesting thought.

I had a glass statue that my sister slid along the surface of a hutch to put it back in position. About 15 seconds after she took her hand off it, we heard a loud *PING* and the thing was cracked right in two.

[Last Dakotan]

To my way of thinking the vibrations resulting from the repairs may have contributed...

Fatigue is from cyclic loading, heavy truck rolls on, heavy truck rolls off, heavy truck rolls on... etc.

You get the picture.The crack is opened and closed repeatably and works it's way through the member.

[ninonitti]

“If it’s not Scot.....it’s crap”