The third program modeled the effect of heat on the strength
and durability of the buildings’ components. The detailed calculations, for example, worked out the deformation of steel beams that received more
heat on one side than the other.
The fourth and most complicated stage
of modeling tracked how deformation of
the buildings’ structural components threw
new stresses onto adjoining components,
ultimately causing failure. The program calculated, minute by minute, the changing
position of each building’s structural elements until that building almost reached
the point of collapse.
The modeling was quite an achievement,
says Jean-Marc Franssen, research director of the National Fund for Scientific
Research in Liège, Belgium. “Until about
10 years ago we modeled all buildings as
2-D skeletons,” he says.
The NIST simulation, like all models of
building failures to date, couldn’t follow the
9/11 collapses through to the end. No com-
puter is yet powerful enough to follow the FIRE IN THE HOLE — Scientists lower
chaotic sequence of events that ensues when a piece of a steel beam into the furnace
components break apart and a building chamber of one of the largest fire-testing
falls, but this is where research is headed. facilities in the United States. It opened at
Franssen and his colleagues have recently Michigan State University in East Lansing
made a breakthrough in modeling the col- in June.
lapse of a structure. They developed an algorithm that figures out the velocity and acceleration of individual
building components.
That allows the program to calculate what engineers call the
dynamic forces involved in a fast-changing scenario, which makes
the analysis one step closer to replicating a real collapse, Franssen
says. Without the added algorithm, a program must stop at the first
sign of failure, but that point may not reliably
indicate a building’s imminent collapse
because of the structure’s ability, or inability,
to redistribute stresses. “We don’t know much
about the failure mode,” he says.
To fully understand the collapse of buildings, researchers are also attempting to model
the behavior of connections between components in a fire as well as the process of
spalling and the cooling of materials after
the fire is out.
A WELL-LIT FUTURE “Structural engineers spend millions of dollars thinking about
wind and earthquakes, but not at all about
fire,” says Susan Lamont, a structural engineer who studied the fire damage to the
intentionally ignited eight-story building in
Cardington. Fire experts and structural engineers are now joining forces to make fire-resistance design as important and routine
as earthquake-damage protection and wind
proofing of buildings. That trend has begun
to take hold in Europe, she says, and “
gradually, the U.S. is starting to do this.”
The future of design for structural integrity
in fires should be based on risk analysis, Lamont says. Any innovative structure or novel
skyscraper design, she adds, should be analyzed by the modeling
software to predict how a fire might affect its stability. “It’s about
designing a building for the forces and fire, rather than applying
fireproofing and hoping that’s adequate,” she says. ■
MICHIGAN S TATE UNIV.
