Poor design led to I-35W bridge collapse?

Interesting old newsreel - but its replacement ALSO gallops when the wind blows a certain way. This is a difficult site, no doubt.

Brian Whatcott Altus OK

And mentioned the existence of cracks (2001)

Brian Whatcott Altus OK

On Tue, 7 Aug 2007 13:02:12 -0700, "Matthew Beasley" wrote this to Robert Clark:

Without doing even trivial background research, I am tempted to say that the built up trusses give this the look of a bridge rather older than 40 years old, to my eye at least.

Brian W

Hmmm....1935, not the first of that kind, I wouldn't think

Brian W

I almost let this suggestion go in and out. But setting out a few survey camera tripod points round a structure for a yearly shot, would be just so cost-effective, it sounds like a winner.

Setup cost could hardly be more than $1,000 per bridge, and maybe $200 p.a per bridge. What's for a politician not to love about this one?

Shoulda patented the method, Dave!

Brian W

Strangely enough, people NEVER expect bridges to collapse, but they do anyway!

Brian Whatcott Altus OK

If you get rich and famous, and accidentally find yourself in Arridzona, buy me a coffee (if it is not over $2 per cup). I seem to recall mention of doing this with a single time-of-flight instrument, from a single location. Multiple locations will only improve / reduce the granularity.

It will only work if there is significant secular changes in the shape of the structure. I am not convinced there were, and I know we disagree here.

But the fact that corrosion can be so easily overlooked, or visual inspection in many places too difficult to perform...

David A. Smith

It is a very similar design to the I-35W bridge, down to the rather "pointed" joints connecting to the concrete supports. This is a two lane bridge with only 1/5th the traffic as the I-35W which probably helped it to survive 70 years:

Deception Pass Bridge.

Bob Clark

Looking more closely at that image you gave of the Deception Pass Bridge I would say the joints are actually more like the wider ones on the Desoto Bridge rather than the almost point-like ones on the I-35W.

Zoom in on the joints in these images:

Deception Pass Bridge

Bob Clark

Dear Robert Clark:

That had been repaired. The hidden meaning in that is that someone in the state bridge maintenance program KNEW that the bridge had an ongoing problem with fatigue cracks and was satisifed that the patchwork repairs were adequate.

I don't think the joints themselves are pointed, The little pyramids are roofs to keep water and snow off the actual joint hardware, which, if it is built with the standards of the time, should be pinned pivots at one end and rollers at the other.

Ah.

Sadly, wrong. The Big Dig in Mass. is now spending monies on law suits. I'm beginning to think that this is part of a plan, but I used be paid to be paranoid.

Here there was not a murder indictment. (A lady was killed when the top piece of a tunnel just built smushed her.) Now the news is reporting that the cement used in the tunnels was watered down. WTF was the state chemists?

/BAH

This is something I know I know nothing about. Do they have to put pieces back together (like in airplanes) to do analyses?

Was it 8 (or whatever) lanes wide when it was built?

/BAH

Bridge

Correction. That should be pressure increases inversely with the area, which is as the square of the diameter. A support half as wide would undergo 4 times the pressure.

Bob Clark

Short Brothers built flying boats and on one new design the wings tore off at the wing root. The aeronautical engineers did the obvious thing and strengthened the wing roots. Again on take-off the wings tore off at the root. This time the engineers added braces between the wings but even that didn't work, so they added struts. Once again the wings tore off at the roots, and everyone was scratching the heads except the janitor. Overnight he borrowed a drill and without telling anyone drilled a line of holes along the wing roots. The next day the new plane took off and flew perfectly, and when it landed the engineers took it apart to see what was so different, and of course they found the line of drilled holes. An inquiry was held to find out how they got there and the janitor owned up, so they asked him how a lavatory cleaner would know the plane would fly. He said "In my experience nothing ever tears along the dotted line".

bridge.> I-35W bridge.>

Thanks for those links. On my reader the links got garbled. Here they are again:

Burnsville looks back at a rich history by John Gessner Staff Writer Posted 1/7/00

Bob Clark

Dear jmfbahciv:

I don't think they *have* to, but I think they *want* to look at every failed piece.

It looks like, from what I can find, it was 4 lanes wide at design (all lanes within substructure-width), was widened to 6 lanes later, and probably restriped to get the 8 lanes it had at time-of-failure.

David A. Smith

On Aug 4, 3:01 pm, "N:dlzc D:aol T:com \(dlzc\)" wrote: ...

...

An article in todays Minneapolis Star/Tribune newspaper has some disconcerting information about previous inspection reports.

Not only was the superstructure in poor condition, but certain components were "beyond tolerable limits," and one of the bridge's piers had "tilted to the north," they reported.

By 2000, the inspectors wrote that "eventual replacement of the entire structure would be preferable" to redecking the bridge. They added: "If bridge replacement is significantly delayed, the bridge should be re-decked."

That recommendation was repeated in every report afterward, but it never happened.

Since the collapse, public attention has focused on consultant reports in 2006 and 2007 that expressed serious reservations about the bridge. But a Star Tribune review of older reports by state inspectors shows that their concerns had been growing since the mid-'90s. ... However, in every report since 2000, inspectors urged the state to replace bolts in a specific area of the bridge, a job listed each year under "Immediate Maintenance Recommendations." .... "The fatigue cracks in the approach spans that occurred in the late

In 1998, inspectors wrote that "numerous fatigue cracks were found" in the approach spans on the north and south sides of the bridge, which was then three decades old. The report said the cracks were drilled out and the fractured beams reinforced with bolted plates. ... The 1999 report said those cracks were among "areas of major concern," adding that "due to the widespread cracking these areas will now be inspected on six-month intervals."

Later reports recommended only annual inspections. Gutknecht said no further cracking was reported after November 2000, so the monitoring cycle was increased. ... The university's research concluded in 2001 that "fatigue cracking of the deck truss is not likely",...."As a result, MnDOT does not need to prematurely replace this bridge because of fatigue cracking, avoiding the high cost associated with such a large project." ... But MnDOT inspectors continued to express concern about fatigue cracking after the university report and the department asked the engineering design consultant URS to review the bridge's condition.

URS in 2006 expressed concerns that a serious fatigue crack might go undetected because of the difficulty in inspecting parts of the bridge that were difficult to reach. URS recommended steel plating as a fix.

But MnDOT engineers asked URS to come up with other options and the department ultimately chose an alternative that called for increased inspections and repairing any problems found. URS called that option the "most cost efficient," but warned that "the critical issue of this approach is to ensure" that inspectors don't miss any measurable flaws.

Chief bridge engineer Dan Dorgan said previously that MnDOT chose the inspection option because it worried that drilling to add plates might weaken the bridge.