Recent Engineering Debacles 7

[hidalgoe]

HellO:

What have been the results of recent engineering debacles, like Boston's Big Dig concrete section that fell and killed some folks in a car or Katrina meant for PE's as far as liability and ethics are concerned?

 

[HgTX]

More than you ever wanted to know about the Challenger disaster:

http://onlineethics.org/CMS/profpractice/ppessays/thiokolshuttle.aspx

Hg


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[djs]

Indeed many of the so call "engineering disasters" were not from faulty engineering, but for a lack of a better word operator failure. The most notable of these is Chernobyl. The engineers know that the reactor was unstable below a certain power output, and placed many safeties to prevent operation in that region. Enter operators which disabled the safeties.

The I-35 bridge was a similar situation. In this case a lack of preventive maintenance. No design will last forever without adequate maintenance.

Another example of an engineering debacle was the Verazano Narrows bridge.

 

[mauricestoker]

My first marriage would qualify as an engineering debacle. I did learn you can get blood from a turnip.

 

[hokie66]

djs,

The maintenance on the I35 bridge was not too good, but the gusset plates which failed were built as designed, half the thickness they should have been. Then numerous inspections over the years failed to identify the problem, because the assumption was always that the gussets would have been properly designed.

 

[oneintheeye]

but could you not say the bridge was load tested to the design load many times and it was only when this was exceeded did a problem occur?

 

[hokie66]

No, it was never load tested to the design load. The condition when the bridge failed did not exceed the design loading, according to the reports.

 

[davidbeach]

Another example of an engineering debacle was the Verazano Narrows bridge.

Please explain. I've never heard of an engineering problems with the Verazano Narrows Bridge. Or, are you off by 3000 miles and 20+ years and thinking of the Tacoma Narrows Bridge?

 

[GregLocock]

Even Tacoma wasn't a debacle, as designed. Sure they came a cropper because of an unsuspected effect, any newish technology can suffer from that. The debacle was leaving it in use until it fell down, probably not an engineering decision.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[MechEng2005]

I don't know if this is one that has been mentioned, as I don't know the name of the bridge, but...

I seem to recall seeing a video in a class on vibrations/resonance with a bridge twisting back and forth (CW/CCW) during extreme winds. I believe it was in Japan?

Does anybody know anything more? Or is that too vague?

-- MechEng2005

 

[Radagast]

That would be "The Gallopin' Gertie", Tacoma Narrows Bridge.

 

[jorton]

I don't think that the Tacoma Narrows Bridge was really new technology, although some new technology did come from the failure. Historically bridges have progressed by pushing the limits of design until there is a failure. Then we all take a big step back and begin again. The Brooklyn Bridge was built 50+ years before the Tacoma Narrows Bridge, yet it has a cable stay system incorporated with the suspension system to stiffen it against such behavior. Other bridges excluded the stays but used relatively stiff decks to prevent such behavior. The Tacoma Narrows Bridge lacked both, pushing the limits too far. I think it was an engineering debacle caused by hubris from our "advanced" analysis techniques and understandings of materials. I agree that it was a much larger error to leave the structure in use, although I understand that attempts were made to stiffen it.

 

[IRstuff]

see:

http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)#Design_and_construction

The TNB design was on a theory proposed by its ultimate designer that allowed the bridge to use substantially shallower girders 8 ft vs. 25 ft for the conventional design. It was this innovation that allowed the bridge to be built at the cost target.

The bridge collapsed only 4 months after opening, so "leave in it use" wasn't exactly a question. In fact, the bridge collapsed almost coincidentally with the release of the report proposing structural solutions.

TTFN

FAQ731-376

 

[msquared48]

I agree with IRstuff on the girder depth problem. That's what I learned in my bridge design class forty years ago, and this was beyond the edge of the envelope design.

The failure was due to intermittent vortex shedding due to a constant wind speed that incited a primary torsional resonant frequency in the structure - a concept never priously investigated for such structures. It is now...

Since we have constructed two new suspension bridges at the same location with deep trusses.

Mike McCann
MMC Engineering

 

[MikeHalloran]

Here's a story about a bridge with proportions almost as extreme as TNB:

http://www.americanheritage.com/articles/magazine/it/1999/2/1999_2_10_print.shtml

It's still standing, though it has been stiffened a bit.

Recommended, as accessible to non-bridge people like me, and not full of journalistic bilge tripe.



Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

The fairing solution to the Deer Island bridge was one of the recommendations for the TNB, 5 days before it collapsed.

TTFN

FAQ731-376

 

[plasgears]

What caused dancing bridges in modern times was the rejection of stiffening trusses in favor of deep girders. Karman vortices were generated by the cyclic generation of vortices beyond the beams. [Aerodynamicists are familiar with this in wing work.] Many bridges were built this way, but they were fixed in several ways; stays, trusses, etc.

The Whitestone bridge in NYC was a contemporary that was stiffened after the fact. In later years the stiffening was removed after introducing smooth fairing in the bridge section profile.

 

[jorton]

Again, I don't think this was innovation. Prior lessons learned were forgotten, and advances in practice gave misplaced confidence. To me this is clearly a debacle. Below is a discussion from the Washington State DOT's website discussing the failure. The full article can be read at

http://www.wsdot.wa.gov/tnbhistory/Machine/machine3.htm

"Blind Spot"-- Design Lessons of Gertie's Failure
At the time the 1940 Narrows Bridge failed, the small community of suspension bridge engineers believed that lighter and narrower bridges were theoretically and functionally sound. In general, leading suspension bridge designers like David Steinman, Othmar Amman, and Leon Moisseiff determined the direction of the profession. Very few people were designing these huge civil works projects. The great bridges were extremely expensive. They presented immensely complicated problems of engineering and construction. The work was sharply limited by government regulation, various social concerns, and constant public scrutiny. A handful of talented engineers became pre-eminent. But, they had what has been called a "blind spot."

That "blind spot" was the root of the problem. According to bridge historian David P. Billington, at that time among suspension bridge engineers, "there seemed to be almost no recognition that wind created vertical movement at all."

The best suspension bridge designers in the 1930s believed that earlier failures had occurred because of heavy traffic loading and poor workmanship. Wind was not particularly important. Engineers viewed stiffening trusses as important for preventing sideways movement (lateral, or horizontal deflection) of the cables and the roadway. Such motion resulted from traffic loads and temperature changes, but had almost nothing to do with the wind.

This trend ran in virtual ignorance of the lessons of earlier times. Early suspension bridge failures resulted from light spans with very flexible decks that were vulnerable to wind (aerodynamic) forces. In the late 19th century engineers moved toward very stiff and heavy suspension bridges. John Roebling consciously designed the 1883 Brooklyn Bridge so that it would be stable against the stresses of wind. In the early 20th century, however, says David P. Billington, Roebling's "historical perspective seemed to have been replaced by a visual preference unrelated to structural engineering."

Just four months after Galloping Gertie failed, a professor of civil engineering at Columbia University, J. K. Finch, published an article in Engineering News-Record that summarized over a century of suspension bridge failures. In the article, titled "Wind Failures of Suspension Bridges or Evolution and Decay of the Stiffening Truss," Finch reminded engineers of some important history, as he reviewed the record of spans that had suffered from aerodynamic instability. Finch declared, "These long-forgotten difficulties with early suspension bridges, clearly show that while to modern engineers, the gyrations of the Tacoma bridge constituted something entirely new and strange, they were not new--they had simply been forgotten."

An entire generation of suspension bridge designer-engineers forgot the lessons of the 19th century. The last major suspension bridge failure had happened five decades earlier, when the Niagara-Clifton Bridge fell in 1889. And, in the 1930s, aerodynamic forces were not well understood at all.

"The entire profession shares in the responsibility," said David Steinman, the highly regarded suspension bridge designer. As experience with leading-edge suspension bridge designs gave engineers new knowledge, they had failed to relate it to aerodynamics and the dynamic effects of wind forces.

 

[IRstuff]

The choice between "innovation" and "debacle," I think, is really a matter of semantics.

The TNB's depth to width ratio of 1:350 is not, and was not, found on any bridge. To that degree, it was an envelope push, hence, an innovation. The fact that history was ignored, and that only deflection theory was used, as exemplified by Moisseiff's 1933 paper on lateral loading that justified such as design, was a debacle.

TTFN

FAQ731-376

 

[GregLocock]

Hang on, were previous suspension bridges built deeper in order to eliminate aerodynamic instability, or for other reasons which then happened to make them immune to flutter?

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[IRstuff]

I think it was more the case that the "traditional" design used trusses, which were design to carry the entire load of the roadway and lateral forces. Moisseiff and others showed that the cables them selves carried a substantial portion of the static deflection loads, so the trusses weren't needed for that, and that smaller plate girders could handle the remainder of the static loads.

However, it was also about that time that people finally understood the effects of the aerodynamics, which were drastically influenced by the blunt plate girders. Moreover, it was clear in hindsight that the stiffer truss designs were also stiffer in torsion, but they were never intentionally designed with that in mind.



TTFN

FAQ731-376