By JEFFREY R. YOUNG
A few days after the terrorist attacks on the World Trade
Center,Abolhassan Astaneh-Asl stood at a recycling center in
New Jersey, staring intently at some 10-ton steel beams that
had once held up two of the world's tallest buildings. They
looked like giant sticks of twisted licorice. But Mr.
Astaneh-Asl, a professor of structural engineering at the
University of California at Berkeley whose specialty is
structural damage done by earthquakes and terrorist bombings,
saw a detailed story in the bends and cracks of the buildings'
He has been examining countless pieces of steel taken from
Ground Zero as part of an effort to build a detailed computer
simulation of the towers' last moments. Once the computer
model is finished, Mr. Astaneh-Asl and his colleagues will
virtually reenact the disaster in an effort to understand
precisely how the planes brought the structures down, and
whether skyscrapers can be built to withstand such attacks.
His investigation -- supported by a $45,000 grant from the
National Science Foundation -- is something like an autopsy of
the landmark buildings. And it has already yielded important
clues, he says. He and other researchers say that such
computer-aided research projects could provide new insights
into building design.
What looks like a giant bite taken out of one piece of steel,
for instance, might have been caused by one of the hijacked
planes' engines slamming through the column, a hollow,
rectangular, steel tube three feet wide and 18 inches deep.
The fact that the piece is still partially intact suggests to
Mr. Astaneh-Asl that it remained standing after impact. He
says the buildings might have survived the plane crashes if
the ensuing jet-fuel fires had not weakened the upper floors
and started a "pancaking collapse."
To support his theory, he cites the way the steel has been
bent at several connection points that once joined the floors
to the vertical columns. If the internal supporting columns
had collapsed upon impact, he says, the connection points
would show cracks, because the damage would have been done
while the steel was cold. Instead, he describes the
connections as being smoothly warped: "If you remember the
Salvador Dali paintings with the clocks that are kind of
melted -- it's kind of like that. That could only happen if
you get steel yellow hot or white hot -- perhaps around 2,000
"The buildings did well under circumstances," he says, arguing
that the steel "was holding the load until the floors
collapsed." He points out that the World Trade Center's
ability to stand for about an hour after the initial impacts
probably saved the lives of more than 20,000 people who
escaped during that time.
Mr. Astaneh-Asl has set up an office in Jersey City, at one of
the two recycling facilities that are processing steel beams
pulled from the wreckage of the towers. The facility is run by
Hugo Neu Schnitzer East, a scrap company that donated the
office space and is helping the professor in his work. He
spends days at a time away from Berkeley, examining what he
calls the "hills of steel."
As of late last month, the recycling center had collected
about 12,000 beams, according to Bob Kelman, senior vice
president of the company.
Mr. Astaneh-Asl has devised a classification system to group
the various types of damage, and has enlisted the help of
workers at the recycling center, training them to spot metal
beams that might yield clues. Among the features he asks
workers to look for are intense "fire burn" and any unusual
bending patterns in the metal. Workers take digital photos of
the steel that they process, he says, and save pieces that
Officials did not originally consider the steel useful to
their investigations, and so at first it was consigned to be
melted down without examination. In fact, the column with the
bite out of it was being cut into pieces when Mr. Astaneh-Asl
saw it and asked to save it.
"The most important contribution of my career was to go to New
York right after the attacks," he says. Like so many people
who rushed to the scene, the researcher says he hoped he could
do something to help. Visiting the site just after the attacks
was "a really horrifying experience," he says. It looked "like
a piece of video taken from Hiroshima documentaries."
But his initial visit paid off: "It ended up making it
possible for future researchers to have the steel saved." The
Smithsonian Institution's National Museum of American History
recently contacted Mr. Astaneh-Asl about acquiring key pieces
of the twin towers for preservation.
Only the Beginning
Examining physical evidence from the site is only the
beginning of his project. Next year, the professor plans to
take a sabbatical from Berkeley to focus his attention on
using computers to create a "full-fledged, realistic model of
the whole World Trade Center -- including other buildings, not
just the towers."
"Then we'll bring the plane in -- to the computer model -- and
hit the building with various scenarios."
To create the model, Mr. Astaneh-Asl plans to work with David
B. McCallen, director of the Center for Complex Distributed
Systems at Lawrence Livermore National Laboratory. They have
worked together in the past, most recently on a computer model
showing the effects of earthquakes on San Francisco's Bay
The two researchers plan to use specific data from Mr.
Astneh-Asl's on-site investigation, going so far as to
incorporate details from individual steel beams into the
Some of the beams have identification numbers stamped onto
them, pinpointing where they were in the buildings. That
information might let researchers who are reconstructing the
catastrophe to work backward, from the damage done to the
beams back to their original location.
"It will get down to modeling the individual elements," says
Mr. McCallen. The simulation will be designed, he says, to
pre-sent the "complete collapse in excruciating detail."
While computer models have become commonplace in engineering,
Mr. McCallen says it is unusual for engineers to make such a
detailed model of an actual collapse. But this model will show
researchers how the World Trade Center's building materials
reacted to extreme forces. "That makes the simulation more
challenging and more difficult," he says.
Testing Virtual Buildings
The model will also allow researchers to test how various
structural changes -- such as increasing the fire-resistant
materials built into the floors -- might have helped prolong
the survival of the towers and possibly save more lives.
"Engineers in an earlier period would have built [physical]
models and tested them," says Jeffrey K. Stine, a curator of
engineering and environmental history at the American-history
museum. "Here you're doing it virtually."
Priscilla P. Nelson, director of the Division of Civil and
Mechanical Systems at the National Science Foundation, says
the World Trade Center simulation "could lead to the
generation of new computer models that will really enhance our
ability to understand structural response." That could help
make new buildings safer in the event of earthquakes or
Mr. Astaneh-Asl is not the only researcher working on computer
models of the destroyed buildings. A team from the American
Society of Civil Engineers that is assessing the terrorist
damage in New York and at the Pentagon, outside Washington,
plans to use computer simulation in its investigation, says W.
Gene Corley, the team's leader, who is senior vice president
of Construction Technology Laboratories, a materials-testing
company in Skokie, Ill.
"Definitely, computer modeling will be used by everyone who
investigates it," he says. "Our fire people are modeling the
fireball, because we want to know how much of the fuel was
consumed" in the jet-fuel fire that raged after the second
plane hit the World Trade Center. "We also are modeling how
the fire developed and spread through the buildings."
'Just One Small Tool'
Some engineers, however, question the usefulness of creating a
finely detailed computer model of the attack on the twin
"The story of what took place there is not going to be
revealed by some magic computer analysis," says Barry J.
Goodno, a professor of structural engineering at the Georgia
Institute of Technology who is a program coordinator for the
MidAmerica Earthquake Center. "Computer simulation is just one
small tool, but I don't see it as a key component at all."
Mr. Goodno, who has been to Ground Zero as part of another
team assessing the damage there, says the most important task
is old-fashioned, hands-on study of the debris, which provides
the raw data without which the computer models would be
Even before September 11, Mr. Astaneh-Asl had been working on
a new design to help protect buildings from terrorist attacks
-- though he says he was thinking of weapons like car bombs or
shoulder-launched missiles rather than airplanes. He says his
proposed design -- which involves bolting concrete slabs to
sheer, steel-plated exterior walls -- might keep the
fuel-filled wings of a plane from getting inside a building in
the event of a similar attack.
Mr. Goodno, however, argues against trying to devise elaborate
ways to make buildings terrorist-proof. "We can't afford to
make buildings blast-proof or earthquake-proof," he says. He
believes that engineers should focus on helping buildings
stand long enough to allow occupants to escape. "The most
important part of the building," he points out, "is the
Mr. McCallen, of Lawrence Livermore, hopes that a computer
model will help to determine whether fortifying skyscrapers
against attacks is economically feasible. "Does it make
sense," he asks, to plan for extreme events?
Or "is it so far out there, and should we just worry about not
letting an airliner hit one of these buildings?"
One way or another, Mr. Astaneh-Asl predicts, people will
continue to build skyscrapers, and continue to improve their
"There's no question whether skyscrapers will be there or
not," he says. "The human spirit is much, much stronger than
these things. For 10,000 years, structural engineer-ing was
the place where humans showed their spirit of conquering. And
by building these tall buildings, you conquer something more
valuable than just making space for living."