Pre-collapse photos show bends on bridge ( Minnesota )

The Associated Press...Star Tribune ^ | Mar 23, 2008

[george76]

Old photos of the Interstate 35W bridge show two steel connecting plates were visibly bent as early as 2003 — four years before the span collapsed into the Mississippi River, killing 13 people.

Minnesota Department of Transportation officials declined to say when the state first knew about the bending in the pieces of steel, called gusset plates.

Two photos, part of a report issued earlier this month by the National Transportation Safety Board, reveal slight bends in gusset plates that hold beams together at two separate connecting points. The plates are in areas believed to be among the first points of failure when the span collapsed.

The NTSB's Office of Highway Safety confirmed that the bowing is part of the investigation into why the bridge collapsed Aug. 1, NTSB Chairman Mark Rosenker didn't comment on the photos, but has said the original design for the bridge specified steel for those and other gusset plates that was too thin.

NTSB spokesman Terry Williams told the Star Tribune the bowing is among "the many things that we are looking at as part of this investigation."

The newspaper said inspection records make no mention of repairs to the bending gusset plates.

Since the bridge's construction during the 1960s, the state highway department had increased weight on the bridge by adding a layer of concrete to the deck in 1977 and by installing concrete barriers in 1998. And the NTSB said last week that, at the time of the collapse, more than 191 tons of construction material had been piled over the bridge's weakest areas.

[janetjanet998]

but the steel would of had to buckle alot more then that if that was the cause of the collapse....

Its safe to assume that it buckled more with time until the collaspe(if that wa sindded the cause)...so why didn’t the inspectors look at these areas later

[kidd]

I do nuclear power plant failure analyses, not structures...but a bent gusset plate suggests a bad generic design, not a part failure.

I would’ve shut the bridge down immediately (regardless of the inconvenience to the public), called for a review of the stress analyses, a detailed inspection of other affected parts and a complete repair of all affected components. But thats how the nuclear industry works.

[Old Sarge]

And it was what, not four minutes before somebody said “Bush’s Fault!’ in the MSM...

[janetjanet998]

I wonder how commom something like that is on bridges

[river rat]

The first thing that came to my mind - is the engineer who designed the plates, must have believed that the number of rivets were more important than the THICKNESS and STRENGTH of the materials being riveted together..

In such a critical application - I’m shocked at the thinness of the plates used to secure the beam members...

I would want to see a plate at least 3 times the thickness used — if FIXING the members and prevent movement was the design objective...

Hell — it looks like they used a too thin plate and popped a few hundred rivets into it thinking the rivets would increase the the strength of the UNRIVETED expanses of the sheet.

What they accomplished was securely fastening a thin member between two shifting beams, and over time the FLEXING fractured the sheet, leading to a catastrophic failure and the whole assembly collapsed.

I’m surprised this design was ever proposed or approved by any Civil Engineer.....

[Moonman62]

After all this information, it’s amazing the bridge lasted as long as it did.

[TheBattman]

But at least they got their light rail project funded!

Priorities....

[the invisib1e hand]

But thats how the nuclear industry works.

guess we ought to be thankful it wasn't a nuclear bridge.

[janetjanet998]

It may have been Ok for the amount of weight in 1967...but like the article says they added more concrete over the years..

So can you even sue the orginal maker of the bridge? How is that their fault that 40 years into the future the thing was overloaded by more concrete and huge contruction equipment.

[B4Ranch]

>I would’ve shut the bridge down immediately<

and you would have been overruled by your superiors just as quickly.

Who the hell do you think you’re talking to? I am the Governor of this State! You will not close down a section of the freeway and cause economic disaster to my State! Now get out of my office before I have you arrested.

[river rat]

I’m not a Civil Engineer - but BRIDGES should not be designed for the CURRENT anticipated loads...

Bridges must have a design life equal to the service life expectancy of the bridge — something like 50 years or more..

That damned plate looks so inadequate - it should have caught someone’s attention on the drafting board!

[Greysard]

The bends are not severe, but they indicate that there were forces on the plates that weren’t kosher.

Once the bending starts, it weakens the part immediately and extensively. Take a thin wooden or plastic plank, set it vertically and push on it. It will resist for a while, being still straight. But once it starts bowing, it takes very little additional pressure to fold it in half or break. That is because the pieces of the plank switch from compression load (which is fairly good) to bending and stretching, which for most materials is not good at all. Just imagine pushing on a vertical glass tube. Once the first crack starts, the part is lost.

[HighWheeler]

“Whole lotta stupidity going on in this Socialist Paradise.”

— — —

yep. read my tagline.

[ltc8k6]

It was announced a while ago that the gusset plates were only half as thick as they were supposed to be.

http://enr.construction.com/news/transportation/archives/080115.asp

[river rat]

Bingo!

See my post #25...

AH SO....it was SUPPOSE to be 2x thicker...

It’s encouraging to learn that my instincts are still relatively intact!

They got me home and they saw this screw up...

However — if they were suppose to be 2x thicker - then the prudent engineer would have added at least another 50% safety factor since this was a bridge in a FREEZING environment HIGH over WATER in a GROWING metropolitan area.....as part of the INTERSTATE HWY system.

[HighWheeler]

“It was announced a while ago that the gusset plates were only half as thick as they were supposed to be.”

- - - -

So now the libs will go on a hunt for “The Culprit”.

The Culprit is defined as anyone that ever touched that bridge plus has deep pockets. And they can’t affect the next election.

[Bean Counter]

Has this bent gussett plate the site of the initial failure in the collapse?

[RayChuang88]

I said shortly after the bridge collapsed that if you've seen pictures of the bridge, it was essentially a disaster waiting to happen. Between the spindly and EXPOSED steel structure that was subject to the temperature and moisture extremes of the Minneapolis, MN area and the whole bridge being held up at four small points on a thin concrete piling, I'm surprised the bridge didn't collage years earlier.

[HighWheeler]

Yeah, they should have been at least as thick as the steel in the U-Channel or I beams, which looks to be at least twice as thick as those thin plates. After all they are expected to carry some of the load from those beams.

[sgtyork]

My BIL’s company - global engineering firm inspected that bridge in 2004(I think) and advised of needed repairs. The report is available on the web. Poor design compounded by incompetence. Can’t wait till theymanage our healthcare.