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RE: FORENSICS: World Trade Center Bombing

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A couple of months back, I watched a movie about the WTC Bombing at HBO.
Most of the terrorists are successfule college graduate with chemical and
electrical engineering degree (based on the movie). But after years of
hardwork and training, they are still dumb in our trade. They didn't even
consider the services of a  structural engineer. But thank God for that.
Great damage was averted.

A. Yango

> ----------
> From: 	William Keil[SMTP:WJK(--nospam--at)]
> Reply To: 	seaint(--nospam--at)
> Sent: 	Wednesday, November 03, 1999 9:49 PM
> To: 	'seaint(--nospam--at)'
> Subject: 	RE: FORENSICS: World Trade Center Bombing
> I was one of the 'structural' engineers involved in the reconstruction of
> the WTC after the February 1993 explosion.  My time on site was
> approximately 11 months.  I seem to recall an extensive article in ENR on
> this topic also.  
> The following is my opinion based on what I observed:
> Two of the subgrade bracing diagonals were damaged.  One was next to the
> bomb and completely blown off and through several walls (the steel
> diagonal
> is now a lawn sculpture at the structural engineering company owner's
> house
> in CT) and the other was bent.  Several of the floor beams adjacent to the
> bomb suffered local web and flange crippling but did not collapse.
> Approximately two to four of the main box columns had cracked welds.
> Several CMU walls and other architectural elements were damaged due to the
> explosion and resulting fire.  At no point do I believe that the tower was
> in danger of collapsing; yes, it would not perform as designed but with
> redundancy of the structural members, all loads would have found another
> safe path.  The shock wave appears to have "reflected" off the more highly
> loaded tower structure into the adjacent six-level below grade mechanical
> and parking structure.
> The mechanical and parking structure did not fare as well.  The concrete
> flat plate floors collapsed progressively to the chiller plant on level
> B5.
> The plaza level had a hole blown through it (about where the van was
> parked)
> and several steel connections had cracked welds, but did not collapse.
> The
> steel columns with practically intact shearheads were still standing
> unbraced about forty feet instead of the design interval of ten feet.  The
> emergency effort was to brace these columns to prevent the collapse of the
> plaza level above. 
> Reconstruction efforts took about two years to finish.  The towers were
> opened in about a month after the event after being extensively cleaned
> and
> updating the security of the complex. 
> In summary, the WTC towers were designed to withstand the impact of a
> large
> passenger plane common in the late 1960s traveling at landing speed due to
> the relative proximity to three airports (JFK, LaGuardia, and Newark).
> However, the wind loads determined by wind tunnel testing were the
> governing
> load case.  After reviewing all the information, a bomb placed adjacent to
> one of the tower columns is not sufficient to endanger the tower.  Several
> steps similar to imploding operations would have to be done to take down
> the
> WTC towers which I am thankful that the "terrorists" will never have an
> opportunity to do that.
> William J. Keil, P.E.
> -----Original Message-----
> Subject: FORENSICS: World Trade Center Bombing
> In the last twenty years, the media have entertained far too many
> "Chicken Little experts" proclaiming that terrorism is at our
> doorstep. For that reason, we have become somewhat desensitized to the
> issue and view it as a distant problem (unless, of course, you are
> from New York, where Islamic terrorists came very close to collapsing
> one of the World Trade Center towers with a bomb).
> This leads me to ask: "How close" DID the bombing of the WTC Tower come to
> collapsing the building? It is so long ago--and I was much less informed
> of
> things structural then--that I can't recall the assessment made by
> structural engineers.