To the U.S. Congress
WTC Collapse Committee (Disaster Commission ?)
Capitol Hill
Washington, DC 20515
Cc:
Leslie E. Robertson Associates
Mr. Leslie E. Robertson
30 Broad Street, 47-48th Floor
New York, NY 10004-2304
New York, March 8, 2002
ONE OPINION AS TO
WHY THE WTC TWIN TOWERS SO EASILY FELL DOWN (2)*
Dear members of the Congressional “WTC Collapse committee”,
The impulse to sit and write down this thoughts came to me after I saw yesterday (March
7, 2002) on TV the hearings before your commission, where some members of the engineering
community have complained about lost forever evidence, about not-provided-to-them blueprints
of the original design of the buildings, about limiting the access to the site for members of the
engineering community on the grounds that Ground Zero has been declared a Crime Scene …
With more of the complaints I do agree, but some of them I perceive more as an excuse
than substantiated complaint … In order to be clear in what I want to say, I will divide this letter
into two major parts: the first one – referring to the lost evidence, to the obstruction (intentional
or mostly unintentional) of collection of evidence, and to the question whether the “lack of blueprints” (which is more of a bureaucratic than practical obstacle) is so decisive for driving conclusions; the second part will be my own opinion as to why the WTC Twin Towers so easily fell
down …
Part 1: Evidence – obstructions and destruction
In such extreme circumstances – like the September 11th disaster, there is no point (and
even it might be immoral) to blame somebody for the initial chaos and lack of preparedness to
act (and react) properly … But the grief, which forever will remain part of the conscience of this
nation (and of people all around the world), must not remain the primary driving force in overcoming the state we were brought to by these inhumane acts! Life is going on – in general for the
humanity, and we are not supposed to loose any chance to learn something from today’s events
The number “2” here indicates that this is a second, more in depth elaboration on my initial opinion expressed in
the original letter with the same title, dated Sept 24, 2001 … See enclosure 3.
*
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in order to be prepared for tomorrow … There is one saying in Spanish, which sounds like this:
“Pregunta sin respuesta es una sabiduría perdida” … In English it will sound approximately as
follows: “Question without an answer is a knowledge lost” …
So, why behind the grief and search for un-recovered bodies (which – no doubt! – should
remain the primary goal) destruction of evidence is taking place? Is this country such a small one
that no sufficient space was found to temporarily store the Twin Towers’ steel for inspection by
specialists before sending it for recycling, not to mention that engineers had to be allowed (in
greater numbers) to see the steel on spot at Ground Zero, where it was in a state that would provide much more hints for the reason of the disaster?
I know that to some people the following questions will not pleasantly sound, but I have
to put them: What is to be blamed for the loss of evidence? Isn’t it this country’s approach to
measure every human move primarily in money numbers? Why the prospective loss of future
knowledge did not prevail over the hurried decision of authorities to recycle these so precious
now pieces of steel? This practice was essentially a drive to rapidly recover some of the investments lost in the destruction of the towers, and to save on necessary space and workforce that
would be involved in this engineering investigation process …
Unfortunately, I have my own experience upon which to drive some of the above conclusions – as far as Crime Scene and on-spot observation are under consideration … One of the
nights between 9/11 and 9/15 when I was volunteering at Ground Zero, I was not “too politely”
expelled from the site by in-clean-uniforms NYPD officers only because I stopped for a short
while with the recovery activity and became suspicious to them with my observation of failed
welds and failed bolt connections … No explanations accepted! They had to follow orders …
And this excuse these days that “blueprints have not been still provided to the engineering investigation committee” … Where are they hidden? … Is it a lack of coordination, negligence in keeping records (something extremely unlikely for this country), or unclear bureaucratic
obstacles … To me it was shameful to hear that six months after the disaster, the ASCE appointed committee ended up using computer model for another building – due to LACK OF DATA
(?) for the WTC Towers … Not only this, I don’t thing a missing blueprint should be an obstacle
in computer modeling … It is to say that, instead of using his/her imagination in the design process, the engineer must rely only on pre-supplied forms and sizes of the structural elements to be
used to form a finished structure …
Part 2: My opinion as to why the WTC twin towers so easily fell down
This will be a trial to elaborate more in depth the thoughts I already expressed in a letter
that I wrote down and tried to distribute in the end of September last year to the mass media, and
later – in the end of October – to the then already established ASCE Teams to Study the NY & DC
Disasters … I don’t pretend to be exhaustive in the case, and I am therefore convinced that more
opinions should be collected from the broad engineering community, instead of only from the
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top already recognized professionals. Such a goal might be achieved, e.g., by establishing an email or a regular mail address – widely publicized for the purpose …
The starting point for my conclusions is the initial observation on TV during the first
post-disaster hours of September 11th … The second to fall – the Northern Tower, was very clear
example for the way both were destroyed: It was a process of domino-like level by level outward
detachment of structural pieces, which later I saw at Ground Zero were three-floor-high column
triads (enclosure 8) … On the most famous pictures (one of them herein presented – enclosure 6)
this fact is not readily visible, but it is very clear in a video sequence …
The first thing that comes in mind while observing this type of destruction is the enormous pressure that is being accumulated within the “rectangular tube” (if we can so idealize any
of the towers). Next to come in mind is the weakness of the external wall of said “tube” …
We know that pressure is being distributed in all directions (see figure on enclosure 11).
From the last paragraph on page 107 and Figure 3.4 on page 108 (enclosure 9 herein) of Angus
Kress Gillespie’s book Twin Towers, one can see and learn that the floor-ceiling construction
chosen for these towers has been the possibly most economical one. The only thing it was designed to carry were utility and occupant loads – floor by floor, and definitely not this huge vertical pressure from destroyed above stories … If you imagine each floor-ceiling to be a membrane (which in fact was even not, because it had no “membrane attachment” along its perimeter), we can easily conclude that these “membranes” were the first thing to yield under the massive debris falling down, permitting (in first place) a huge amount of said debris to be accumulated within the “rectangular tube” instead of “overflowing” outside the “tube’s” walls …
In second place comes the horizontal component of said pressure … The only obstacle to
this horizontal pressure would be the very strong walls of the “tube”, which in fact were definitely not designed to be such!
There is one sentence in the FAQ (Frequently Asked Questions) sections of the ASCE
(American Society of Civil Engineers) & LERA (Leslie E. Robertson Associates) web-sites,
which reads: “Structural engineers design the beams, the columns, the slabs, and their connections to resist the anticipated loads” (enclosure 2). This in general sounds proper, but seemingly
does not apply to the design of all Twin Towers’ connection components, especially with regard
to the not anticipated bursting horizontal forces that were the product of the enormous pressure
of the falling upper floors of the towers! After the initial destruction of several floors below the
melted ones, said above forces might have been put under control if the horizontal beams called
spandrels (mentioned on page 107 of said above book – enclosure 9) were provided with connections that guarantee the same tensile capacity as the cross-section of the spandrels would provide … Instead, between 9/11 and 9/15 at Ground Zero I witnessed one-or-two-line bolt connections (enclosure 13, fig. a), which seemingly were intended only to keep in place the columntriads during erection, or during slight (with relatively insignificant horizontal forces) shaking of
the towers during their life … The mere fact that during the very fast review of the book I found
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only one single paragraph dealing with these column triads (on page 107 of the Twin Towers
book – enclosure 9 herein), and I found no word about the connection between them confirms
the fact that outward bursting horizontal forces have not been accounted for, that no PERIPHERAL TENSION was considered, and, in general, that those specific connections have not been
considered to be of great significance …
On page 78 (enclosure 7) of the book already mentioned we can read that “in the WTC
buildings, the exterior walls carry the vertical loads as well as resisting all lateral winds” …
Yes, but winds are horizontal loads directed inwards to the building, and therefore are being able
to be redistributed to the internal core columns through the floor frames. The bursting outward
horizontal load, though, cannot be so redistributed due to lack of tensile elements between the
core and façade columns. The thirty-two-inch-deep trusses, or triangular metal frameworks, as
discussed on page 107 of said book (see enclosure 9) definitely cannot serve for the purpose, and
trusses in general are not designed as tensile elements! … As Dr. Thornton has suggested during
a November 12, 2001 forum on the WTC disaster in Columbia University, cross beams running
continuously through the building (see enclosure 5, and fig. b on enclosure 12) could do the job
as such tensile elements. In my opinion, though, [as mentioned in my September 24, 2001 letter
– enclosures 3 & 4] horizontal beams forming a ring along the perimeter of the building floors
would have served better for the purpose (see fig. a, enclosure 12), because the relatively uniform tension along them would have better redistributed the horizontal outward bursting forces to all façade columns … Given this thoughts, I hope, the reader would agree that the sentence
“These tough exterior walls had the strength to resist the enormous force of lateral winds” on
page 79 (enclosure 7) of the Twin Towers book is valid only for enormous [inward] lateral forces, but not for enourmous [bursting outward] lateral forces …
It is obvious that both suggestions discussed in the paragraph above would increase the
total weight of the towers (and therefore their cost), but how many lives could have been saved,
together with 2/3 to 3/4 of the buildings themselves …
Another significant deficiency of the façade column design is the practically absent connection for tensile forces between any two rows of column-triads one over the other (enclosure
13, fig. a) … The bolts that vertically unite the column triads were only 4 or 6 on each of the
three columns of a triad – according to my observation – most of them cut off during the disaster.
Apparently, these external columns were intended to carry only axial vertical loads …
Weak point (according to me) were also the non-full-penetration welds in the massive
central (building-core) columns, which implies that said columns (and probably others) have
been expected to work only under compression, and much less (if at all) in bending and tension –
which were actually the destructive conditions we witnessed … When you expect only compression to be transferred, it is sufficient for you to rely on contact of surfaces, but in order to transfer
tension, continuity should be provided with full penetration welds – which means that the cross
section we have in the element should be replicated in the connection of two adjacent elements
(see fig. B, enclosure 13) …
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Let me finish with the words of Mr. Leslie Robertson – the structural designer of record
for the Towers, with which he concludes an interview with him: “There’s no end to the number
of ways that man can do harm to man” (New York Academy of Sciences “Update” Magazine –
Jan/Feb 2002 – see enclosure 1) … Given this undoubted reality, there’s no point for plane
crashes to be the decisive design-against issue in public buildings (as is seemingly the nowadays
trend) … Rather, better fireproofing and better general resistance to any-direction-in-space
events should be the issue …
Everyone would probably agree that not every possible event can come to the imagination even to the most diligent and ingenious designer, but we can strive to keep in mind such
“new events” after we once witness them … Missing the opportunities to timely study them is
simply unacceptable …
Sincerely,
Mario Behar
Columbia Univ. Station
P.O. box 250315
New York, NY 10025-1535
(718)-728-4937 (tel.); (718)-956-8873 (fax)
e-mail: mbehar7@earthlink.net
ENCLOSED with this mail:
1) Interview with Mr. Leslie Robertson – the structural designer of record for the Towers, New York
Academy of Sciences “Update” Magazine – Jan/Feb 2002;
2) The FAQ (Frequently Asked Questions) section of the LERA (Leslie E. Robertson Associates)
web-site;
3) The first letter of opinion (Sept 24-27, 2001) as to Why the WTC Twin Towers so easily fell
down of the author of the current letter;
4) The e-mail with which the above said first opinion has been forwarded to the ASCE Teams to
study the NY and DC Disasters (Oct 25, 2001);
5) The “NY Times” article (Nov 13, 2001) reporting the November 12, 2001 forum on the WTC disaster in Columbia University, NY;
6) One of the most famous pictures of the North Tower crumbling down;
7) Pages 78 & 79 of Angus Kress Gillespie’s book “Twin Towers” with a figure showing the vertical load bearing wall columns and core-of-building columns;
8) Page 105 of Angus Kress Gillespie’s book “Twin Towers” with a figure showing the typical
three-story façade column-triads;
9) Pages 107 & 108 of Angus Kress Gillespie’s book “Twin Towers” with a figure showing floorceiling construction;
10) Typical view of the Towers during erection (Figure 3.1 on Page 94 of Angus Kress Gillespie’s
book “Twin Towers”);
11) Rough presentation of how the destruction might have occurred;
12) Rough presentation of my (of the author of this letter) concept of barrel rings along the perimeter of the building (fig. a), and Dr. Thornton’s idea of cross-beams running continuously through
the building (fig. b), which might be also considered as two components of one common consept;
13) Rough presentation of Weak connections: between façade column-triad panels (fig. a), and between portions of the building-core massive columns (fig. b).
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figure a. Weak connections between façade column-triad panels
figure b. Weak connection between portions of the building-core columns
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figure a. “Barrel” rings along the perimeter of the building (the author of this letter)
figure b. Cross-beams running continuously through the building (Dr. Thornton)
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