Scholars Work to Rebuild the World Trade Center Virtually

   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'
  charred remains.
  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.
  'Pancaking Collapse'
  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
  look unusual.
  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
  computer model.
  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
  terrorist attacks.
  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
  Extreme Events
  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."