] [Thread] [Date] [Author]

["Carter, Charlie" <carter(--nospam--at)aisc.org>]

>I was convince that when the dust
>cleared, most of the building 
>would at least be standing.
>I'd be real curious if anyone on
>the list got the same shock I did.

I'm with you, Chris. There are only three people I know who have said they
expected collapse when first seeing the inpact. And I only believe one of
them. After the fact, however, the chain of events makes horribly perfect
sense based upon everything we do know about structural behavior.

>I don't think the profession should be
>blowing the issue off by shrugging our
>shoulders and saying, 'Not our fault.'
>The issue doesn't need to turn into a
>witchhunt, but structural engineers
>would do well to begin factoring it
>into their thinking. 

I agree here as well, but I think we have started out of the gate in the
wrong direction.

In all that we do, we define loading, serviceability and other criteria that
must be met. Then we use our understanding of response and strength to meet
those criteria. But in the emotion, shock, horror and drive to "solve" 9/11,
there are already some prescribed solutions being bandied about, such as
requiring different shaft wall construction. Yet we don't even know if those
"solutions" would have performed any better, except by gut feel. For
example, would the stairways have still been intact if the shaft walls were
masonry or concrete? I don't know, but I tend to doubt it because a plane is
a pretty massive object and I do know that concrete cover in the affected
area of the Pentagon was as non-existant as spray-applied fire protection in
the affected areas of the WTC towers after the plane impact.

Also, to what extent should the tragic but rare events of 9/11 change our
every day practice on the average building design? It is not a given in my
mind that sweeping changes should be unilaterally made. In this regard, Bob
Johnson's sentiments are appropriate. Perhaps it may be that the best way to
spend our money as a society is on airport security technology and
reinforced cockpit doors in aircraft.

Quick fixes and prescriptive changes based upon emotional gut reactions is
no way to advance engineering practice after 9/11. There is a program being
proposed by NIST to do the post 9/11 work necessary to establish engineering
criteria to address the 9/11 experience. We (AISC) are participating in a
broad council of organizations to help guide this effort and maintain a
direct connection to engineering and industry. The council has the following
organizations represented as of right now:

    NCSEA (The National Council of Structural Engineering Organizations)
    CASE (The Council of American Structural Engineers)
    ASCE/SEI (The Structural Engineering Institute)
    CTBUH (The Council on Tall Buildings and Urban Habitat)
    AISC (The American Institute of Steel Construction)
    ACI (The American Concrete Institute)
    TMS (The Masonry Society)
    ICC (The International Code Council)
    NFPA (National Fire Protection Association)
    SFPE (The Society of Fire Protection Engineers)

This group brings together engineering organizations, structural standards
development organizations, and the code agencies for joint participation in
the effort and a more direct connection between the research and development
and the direct implementation of that work.

I'm very optimistic that this previously unheard of cooperation between
organizations will result in meaningful results for the post-9/11 era.

Charlie

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