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RE: FORENSICS: World Trade Center Bombing[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: FORENSICS: World Trade Center Bombing
- From: William Keil <WJK(--nospam--at)brph.com>
- Date: Wed, 3 Nov 1999 08:49:20 -0500
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 [QUOTE MODE ON] 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). [QUOTE MODE OFF] 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.
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