Tacoma Narrows bridge (was: MySQL v. PostgreSQL ...)

[Bill Sconce]

On Tue, 31 Jul 2007 17:53:47 -0400 (EDT)
Ric Werme <ewerme at comcast.net> wrote:

> In that particular case, it was more along the line of inadequate
> wind tunnel and simulation time.  (The slide rules of the day were
> slow and inaccurate.)

I completely agree.  "Inadequate wind tunnel time" may sound a little
more professional than "we just guessed", but the results where it
counts is the same.  For professional engineering the results where
it counts is...that bridges must not fall down.
    "For a successful technology, reality must take precedence over 
    public relations, for nature cannot be fooled."[1]


> When an entire profession learns a lot from a particular bridge,
> blaming it on amateurs is a bit unfair.  And they learned a lot
> before the winds got to strong.

Probaly I was a little unfair.  But I did not mean to blame it on
amateurs as specific persons.  I did mean to blame it on amateurISHNESS,
as in not considering all the real consequences.

"No one could have connected the dots" is not a professional excuse.
If you can't guarantee the results, what you're doing is not engineering.
Experimentation, perhaps.  Experimentation has its place, but not in
bridge building.  (Maybe in software.  But then we don't call it 
engineering.)[2]


> Besides - a lot of current bridges can be taken down surprisingly
> easily. Marching bands break sync crossing bridges, the Golden Gate
> bridge has been closed due to winds and strengthed in response.  

This seems to be two points.  Perhaps marching bands CAN take down a
bridge, but strengthening the Golden Gate bridge would seem to be
a rational (and well executed) upgrade.  Engineering.

In the case of the Tacoma Narrows bridge the aerodynamic resonance had
appeared weeks before, and had even given the nickname "Galloping Gertie"
to the bridge. The point here is that aerodynamic resonance was NOT PART
OF THE MODELLED BEHAVIOR OF THE DESIGN, and was therefore an opportunity
for reality-based thinking.

Amateurishness includes succumbing to the temptation to not think
through to consequences when reality offers new data.  In the Tacoma
Narrows case: "However, the mass of the bridge was considered sufficient
to keep it structurally sound."[3]  And then the torsional mode appeared,
and the longitudinal resonance morphed into aerodynamic flutter, which
was certainly understood at the time even if no bridge had yet been
built to demonstrate flutter occurring in steel and concrete at 0.2 Hz.

In the case of Challenger the O rings had burned through "only" 1/3
the way, although NO burning was part of the modelled behavior of the
design. In both cases the decisionmakers chose a path which satisfied
public relations.  Columbia was a third case: NO foam shedding was part
of the modelled behavior of the design, and in THAT case PR even kept
NASA from looking for possible damage via telescope. That's amateurish:
hoping for the best when reality-based thinking is called for.[4]

now_ask_me_what_I_think_of_web_2.0'ly yrs,
-Bill

___________________________
[1] reality - Richard P. Feynman, in the last line of his famous
    Appendix F to the Rogers Commission report on the loss of the
    space shuttle Columbia,
      http://history.nasa.gov/rogersrep/v2appf.htm
      
[2] engineering - I agree that most software is art, not engineering;
    as Paul Graham holds,
      http://www.paulgraham.com/hp.html
      
[3] considered sufficient:
      http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge
      
[4] hoping for the best: 
    A more recent example, and the event which made me write this,
    the I35 bridge in Minnesota, which collapsed yesterday.  Only a
    dog died when the Tacoma Narrows bridge fell in.  In Minnesota:
    
      "cracks...in the cross girder at the end of the approach
       spans."  - 1997 report
       
       ...the bridge's deck truss "has not experienced fatigue cracking,
       but it has many poor fatigue details on the main truss and floor
       truss system."  - 2001 report
       
       "should not have any problems with fatigue cracking in the
       foreseeable future... [the department] "does not need to
       prematurely replace this bridge because of fatigue cracking,
       avoiding the high costs associated with such a large project."
          - 2001 report
          
    The language in that last paragraph reads just like a NASA
    Powerpoint.  See:
http://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=0001yB&topic_id=1