- Many of his fellow structural engineers were stunned
when the twin towers of the World Trade Center crashed to the ground on
Sept. 11. But not W. Gene Corley, the suburban Chicago structural engineer
who is heading the federal investigation into the collapse.
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- Corley, senior vice president at Construction Technology
Laboratories in north suburban Skokie, is an old hand when it comes to
figuring out why buildings fall down. His roster of past investigations
includes the fatal 1993 fire that occurred during the FBI's raid of the
Branch Davidian compound in Waco, Texas; the 1995 bombing and collapse
of the Alfred P. Murrah Federal Building in Oklahoma City; and the 1999
collapse of a construction crane at Milwaukee's Miller Park. You might
even call him a master of disaster, though he's far too reserved to use
such a jaunty, self-promoting term.
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- When the hijacked Boeing 767 jets hit the Trade Center
that morning, Corley was in his Skokie office, part of a Bauhaus-like
compound
of low-slung modern buildings at 5420 Old Orchard Rd., just west of the
Edens Expressway. Alerted to the disaster in the making, he went to The
Washington Post Web site and found still pictures of black smoke and red
flames shooting out of the lower Manhattan landmark.
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- "I said: 'At least it hasn't fallen yet,' "
Corley told the Tribune in his first extensive interview on the
investigation.
"'But if they don't get the fire out, it will.' "
-
- For years, the 65-year-old Downstate native has quietly
gone about the business of structural sleuthing, amassing bits and pieces
of evidence to figure out why structures that are supposed to stand up
don't. Now he's carrying out that task on a grand stage, heading the
high-profile
inquiry that is trying to pinpoint why the 110-story towers fell.
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- In a sense, everybody already knows what happened on
Sept. 11: When the hijacked planes, gorged with fuel for cross-country
flights, struck the towers, the rupture of the fuel tanks started an
extremely
hot fire that weakened the buildings' structural steel and caused the Trade
Center's deadly crumpling. No building could have survived such a blow,
expert after expert has said.
-
- But things are hardly that simple. No one has
authoritatively
explained why One World Trade Center remained standing for 1 hour and 40
minutes while Two World Trade Center crashed to the ground just 56 minutes
after impact. Another mystery is why smaller, nearby structures remained
standing even though fire and steel from the twin towers rained down on
them and even ripped huge chunks out of their facades.
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- Could the Trade Center's original architects and
engineers
have done anything differently that would have prevented such a large loss
of life -- more than 3,300 victims, according to current estimates? Or
is there reason to be satisfied that the buildings stood up as long as
they did, allowing roughly 25,000 people to escape?
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- Grappling with the Issues
-
- These are some of the issues that Corley and his team
of 23 specialists, who include experts in such esoteric fields as blast
effects, will be grappling with until their investigation wraps up in March
or April. The inquiry is co-sponsored by the American Society of Civil
Engineers, an industry group based in Reston, Va., and the U.S. Federal
Emergency Management Agency, the government entity that tries to prevent,
as well as deals with, disasters.
-
- Much more than solving a structural mystery is at stake.
With America fighting a war on terrorism, highly symbolic structures both
tall and short may require new armor to protect them against fanatics like
the ones who destroyed the twin towers and damaged the Pentagon on Sept.
11.
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- "For those buildings that can be identified as being
particular targets of terrorists," Corley says, "we expect to
have recommendations that will allow the designers to do things differently
that will enhance the safety of the people in the building."
-
- The investigators are looking at several spots where
the collapse might have begun -- exterior columns, interior columns, or
the lightweight steel trusses that supported the building's floors. They
also are challenging conventional wisdom by entertaining this hypothesis:
The planes so damaged the twin towers that a regular fire of 1,100 to 1,800
degrees Fahrenheit, not a superhot fire stoked by jet fuel and reaching
at least 2,000 degrees Fahrenheit, was sufficient to weaken the
skyscrapers'
structural steel to the point of collapse.
-
- Whatever its outcome, the investigation is proceeding
very differently than the one Corley led in Oklahoma City. There, the
nine-story
Alfred P. Murrah Building fell almost instantly, denying investigators
a real-time record of the steps leading to its collapse. The much longer
interval between blast and collapse at the World Trade Center resulted
in the accumulation of a wealth of images (more than 150 hours of videos,
as well as myriad photographs) that are crucial pieces of evidence.
-
- In trying to determine what piece of the skyscrapers
gave way first, for example, the investigators are searching for an
aerial-perspective
video that would show the fall of One World Trade Center. If the
communications
antenna atop the building started dropping before the perimeter of the
building, that would offer a clue that the interior steel columns in the
building's core (which supported the antenna) began collapsing before the
perimeter columns.
-
- In contrast, Corley says, "the only thing we had
in Oklahoma City was an audio tape. There was a hearing on water rights
going on right across the street. They had turned on the recorder at 9
a.m. At 9:01 a.m., the bomb went off. We were able to analyze the tape
and determine from the sound that it took roughly 3 seconds for the
building
to collapse."
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- Specialist in Concrete
-
- After Corley was named to head the Trade Center
investigation,
there was some grumbling among steel industry leaders because the Skokie
engineer is known as a specialist in concrete. The steel people fretted
that Corley would blame the collapse on the steel frame of the Trade Center
towers and say that structures that relied more on concrete, such as the
Petronas Towers in Malaysia, currently the world's tallest buildings, would
have fared better.
-
- The criticism is nonsense, according to Jim Rossberg,
a director at the American Society of Civil Engineers, who is working with
the investigative team. Because Corley led a similar team in Oklahoma City,
"it was very natural that Gene's name came to the forefront,"
Rossberg says. "Gene has tremendous experience in looking at and
organizing
studies and getting the right people involved in the effort. This issue
is not a concrete issue or a steel issue. It's a building
issue."
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- Building is in Corley's blood. His father, a contractor
in Shelbyville, Ill., a small town about 60 miles southeast of Springfield,
built single-family homes, shopping malls and grocery stores. "I was
on building sites even before I was big enough to crawl," he says.
Only one of his father's projects collapsed -- a farm equipment warehouse
that couldn't bear the weight of heavy snow on its roof. But that was the
designer's error, not his father's, Corley hastens to add.
-
- He enrolled in the architecture school at the University
of Illinois at Urbana-Champaign in the 1950s, but opted for engineering
instead. "I cannot draw a picture of a person that looks like a
person,"
he says. "I figured I would flunk my art courses."
-
- He got his bachelor's, master's and PhD in engineering
at Illinois (his graduate adviser, Chester Siess, also tutored the late
Fazlur Khan, the noted structural engineer who worked on both Sears Tower
and the John Hancock Center). Then Corley joined the U.S. Army Corps of
Engineers, for whom he developed a collapsible aluminum and steel bridge
that would pop out of a tank and provide a river crossing for tanks and
troops.
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- NASA vs. Concrete
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- During the mid-1960s, the National Aeronautics and Space
Administration asked him to work on its lunar rover program, but he took
a less glamorous route, joining the Portland Cement Association, a concrete
industry group that in 1997 spun off Construction Technology Laboratories
to become a for-profit research and engineering company. At both Portland
Cement and Construction Technology Laboratories, Corley explored the
effects
of fire on various materials, a body of knowledge that is proving essential
in the Trade Center investigation.
-
- "The aircraft hits wounded the buildings, but they
could have recovered if it weren't for the fire," says Corley, who
has been to Ground Zero four times since Sept. 11.
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- The inquiry centers on three areas:
-
- Fireproofing: Investigators
are trying to figure out whether the impact of the planes dislodged the
fireproofing that was sprayed onto the structural steel of the twin towers
-- an outcome that would have made the steel far more vulnerable to
fire.
-
- To determine what happened, the team will work backward,
estimating the temperature of the fire just before the collapses occurred
by taking samples of the salvaged steel that now sits in junk yards in
New Jersey and a New York City dump. (Surviving chalk marks on that steel
indicate where each piece went in the building.) Investigators then will
use computer modeling to ascertain how long the buildings should have stood
up, both with fireproofing intact and with it knocked off.
-
- "That should give us a pretty good clue" about
whether fireproofing stayed on or not, Corley says.
-
- Escape routes: Based on media
accounts showing that the vast majority of the dead were trapped on or
above the floors where the planes hit, it appears that the stairwells in
the Trade Center were wide enough to allow people on lower floors to get
out and probably would have been wide enough to accommodate those on the
upper floors as well. Elevators apparently operated right up to the time
of collapse, though only on the floors below where the jets struck. (Not
all elevators served the upper floors, and those that did were likely
inoperable.)
-
- As a result, Corley says, investigators are focusing
on what happened on the floors where the planes hit and above. Did the
jets smash through the stairwells, blocking access to escape routes on
these floors? Or did the stairwells remain intact and fire prevented people
from reaching them?
-
- Structure: Corley's team
is seeking to determine which structural elements of the twin towers gave
way first and whether the skyscrapers' unique structural system played
any role in the collapse.
-
- Designed by the late architect Minoru Yamasaki and
structural
engineers Skilling, Helle, Christiansen, Robertson, the twin towers were
each largely supported by a "tube" of closely spaced perimeter
steel columns that formed a rigid box. That contrasts with a more typical
building, in which an internal cage of columns and beams support a
non-load-bearing
exterior "curtain wall."
-
- In another innovation, lightweight steel trusses (rather
than heavier steel beams) supported the buildings' floors and connected
the perimeter columns to the steel columns of each building's core.
Finally,
a pair of bolts (instead of multiple bolts) connected each truss unit to
each perimeter column and core column.
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- Unusual Structural System
-
- The towers' structural system, which was economical
because
it used less steel and took less time to erect, was "unusual and not
really repeated" in other buildings, says one member of the team,
who asked not to be identified. There was "a very dense frame on the
outside -- a good thing. But on the other hand, the [trusses] -- that's
what you see in Kmart roofs -- they're not common."
-
- Corley is less critical of the support network. "The
structural system is a big part of the reason the towers held up after
being hit by an airplane. [The investigators] don't think this was a highly
vulnerable system. We think it did quite well."
-
- The big question is whether this system was more prone
to collapse than a conventional structural network after the planes hit
and the fires started raging. The investigators don't know yet, but they
are looking at two ways that the collapse might have occurred.
-
- After impact, the weight of the columns would have been
transferred to adjacent surviving columns on the perimeter of the building,
with the surviving columns temporarily forming a kind of arch over the
hole made by the plane. Because the remaining columns would have been
supporting
more weight than usual, Corley says, "they don't have to be heated
as much before you have a collapse."
-
- A variation on this theme is that the core columns
collapsed
first. Then, they would have dragged down the floor trusses and the
exterior
columns with them. This would have resembled a classic demolition scheme,
Corley says, in which explosives "take out the interior part
first."
-
- Focusing on the Trusses
-
- The collapse also could have occurred another way: The
floor trusses would have sagged because of the heat of the fire, and the
trusses might have broken free because of the relatively weak connections
between them and the columns. The weight of the trusses would have dropped
onto the floors below, dangerously adding to their load. At the same time,
the perimeter columns would have had no lateral support, causing them to
buckle and fly outward.
-
- In each case, one floor would have "pancaked"
on top of another, with the weight from above bringing the entire building
down. The only difference is which element gave way first -- the floors
or the columns.
-
- Some engineers have speculated that One World Trade
Center
stood longer than its counterpart because it was struck at a higher point
-- around the 90th floor rather than 70th floor, as was the case at Two
World Trade Center. Therefore, the columns beneath the hole had less weight
to support. Such an explanation is plausible, Corley says, but it might
founder because of the fact that the lower columns in the Trade Center
towers were beefier than the higher columns, meaning that they might be
able to handle the added stress on them.
-
- "There is the possibility," he says. "that
the [evidence] won't be conclusive and that we'll never know."
-
- However the investigation turns out, Corley is always
likely to remember how it got started -- with an incredible coincidence
that brought one of member of the team dangerously close to one of the
Sept. 11 terrorist attacks.
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- Calm Conference Call
-
- About 8 a.m. that morning, Corley calmly began a
conference
call with Rossberg and a New York blast effects expert, Robert Smilowitz,
about design standards they had been working on to make skyscrapers and
other non-government buildings better able to resist the impact of
terrorist
bombs. Rossberg, who lives in Virginia and was driving to downtown
Washington,
was speaking on his cell phone.
-
- One World Trade Center had been hit about 15 minutes
earlier, but though the engineers were aware of this, they continued with
their call, thinking that a small private aircraft had accidentally hit
the massive high-rise. They even kept going when Smilowitz, who was in
his SoHo office, reported that another plane had struck Two World Trade
Center.
-
- By a twist of fate, meanwhile, Rossberg had run into
traffic jams and pulled into the parking lot of the Pentagon for respite.
Around 8:40 a.m., he heard a tremendous explosion. The third hijacked plane
had just burrowed itself into the side of the America's military hub,
perhaps
1,500 feet from Rossberg's car.
-
- "At that point, we ended our phone call,"
Corley
says.
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- Copyright © 2001
Chicago Tribune
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