Gene Kohn sits in a conference room in his offices, which occupy five floors of a 16-story
building on West 57th Street in Manhattan. As the 71-year-old, white-haired architect looks
out his window at the midtown high-rises and skyscrapers, his thoughts turn to two particular
buildings.
The World Trade towers were designed beautifully, in the sense that they fulfilled
the goal of the design, Kohn says. Kohn is a founding partner of Kohn Pedersen Fox Associates,
the prestigious architectural firm that has designed the more than 1,500-foot-high Shanghai World
Financial Center in China. When the building is completed in 2007, it will be the world's tallest structure, eclipsing the
1,483-foot-tall Petronas Towers in Kuala Lumpur, Malaysia. Among the other
buildings designed by Kohn's 25-year-old firm are the World Bank in Washington,
D.C., the Federal Reserve Bank in Dallas, and the Goldman-Sachs headquarters in
London.
Kohn is a strong advocate of skyscrapers, contending they are necessary and a much
desired feature of city life. He calls for stricter building codes, but feels that
new skyscrapers shouldn't be turned into fortresses. And he talks about aspects of
the World Trade Center that no one could have known would prove fatal on September
11, when nearly 3,000 people died in lower Manhattan in the worst terror attack on
American soil in the country's history.
I think the worst thing we could do is to stop building important buildings because
we're afraid someone is going to try to destroy them, Kohn says. We have to
realize they are targets, and we have to make our buildings as safe as we can,
without destroying their significance, their beauty or the quality of life that goes
on inside them.
Building and fire codes in China, Hong Kong and Japan, the sites of many new tall
buildings, are more conservative than they are in the United States, and Kohn
suggests that aspects of those codes be considered for future American skyscrapers.
He says the tower his firm is designing in Shanghai will have features that, had
they been in place at the World Trade Center, would probably have better contained
the fire, and the jet fuel that spread it. The safety features, he says, would have
made it easier for firefighters to get to and fight the fire, would have made it
easier for people to escape and would have either delayed or prevented the
buildings' collapse.
The goal at the World Trade Center, he says, was to create the most efficient, the
lightest steel frame structure that, at the height of 110 stories (the taller of the
two towers was 1,368 feet high), could resist wind and earthquakes and support the
heaviness of the building itself. Wind is a major concern in tall buildings, because
the top third of the building gets two-thirds of the wind. It was extremely
brilliant work. These tall buildings are enormously heavy to start with, so the idea
was that if you reduce the weight, you can reduce the cost of the foundation and the
structure, and you can maximize the usable space the developer can rent out.
Yet despite their lightness, The World Trade Center buildings had withstood the
terrorist bombing in 1993, which hit their foundations and columns. Car bombs and
truck bombs are a bigger threat to most buildings than airplanes, Kohn says. And
tall buildings, because of their sheer mass, can resist those forces better than low
buildings can.
But the World Trade Center hadn't been designed to meet the September 11 attacks.
Even today, no architect designs a building to withstand the direct hit of a fully
fueled jetliner, and many engineers say that the attack would have destroyed almost
any skyscraper. (By contrast, Kohn says, the B-25 bomber that hit the Empire State
Building in July 1945 -- 14 people were killed, but the building withstood the
crash -- was like a fly compared to the 767 in its size and weight.)
The World Trade Center didn't come down because of the impact of the planes, he
says. The planes got swallowed up by the buildings, and the buildings didn't fall
over because of the crash. In speaking recently to the World Trade Center's
original engineers, Skilling Ward Magnusson Barkshire (known as Skilling Ward
Christian Robertson when the Towers were designed), Kohn learned that the towers'
design actually helped prevent what could been an even more terrible disaster. (Kohn
emphasizes that his comments are based solely on his own evaluation and on
discussions with engineers familiar with the buildings, and do not have the benefit
of the ongoing detailed analysis and investigation by experts in the construction
and structural engineering fields.)
The impact of a 767 full of fuel flying hundreds of miles an hour is staggering,
he says. It took out about 35 columns. The wingspan of the plane is almost as large
as the width of the building. And yet the buildings withstood it. The tops of the
buildings didn't fall off. What happened was, that because all the buildings' little
columns were tied together horizontally and vertically, the columns above the
openings where the planes entered acted like a giant truss, a bridge, spanning the
distance of the openings. Each column helped the others. Had it been a typical
column and beam system, it would have failed.
That ability to create a span over the opening kept the tops of the buildings from
toppling to the side. If they had toppled that way, the fire would not have
destroyed the rest of the buildings, but the tragedy down below would have been even
more horrendous. The way the buildings eventually collapsed, straight down, actually
prevented an enormous amount of death and destruction.
The buildings collapsed because of a problem no one could have
anticipated -- thousands of gallons of jet fuel burning inside. The temperature of the
burning fuel at the World Trade Center reached close to 2,000 degrees, Kohn says,
and that did not allow the steel frame to survive the two hours or more it was
expected to survive in a typical, less-hot fire -- a fire involving office paper or
furniture, for instance.
The buildings held more than 200,000 tons of steel, 425,000 cubic yards of concrete,
and 600,000 square feet of glass in 43,000
windows. Each floor, a reinforced concrete pad on a metal deck supported by steel
cross beams, was about one acre and weighed about
4.8 million pounds. Engineers believe that the intense heat from the jet fuel
weakened and buckled the steel framework -- the columns and trusses holding up the
individual floors. As a result the upper floors collapsed and started an unstoppable
chain reaction created by the force of gravity. The south tower collapsed 56 minutes
after impact. The north tower lasted an hour and 40 minutes.
The Trade Center was a steel frame on the outside, Kohn says, with very small
columns with spray-on fireproofing on the exterior, and 2-inch-thick gypsum board,
or Sheetrock, for fireproofing on the interior. The central core of the building -- the
wall that encloses the elevators, the fire stairs and the air shafts -- was also steel
frame, and also used the 2-inch Sheetrock for fireproofing. It was one of the first
buildings, perhaps the first, to do so. The 2-inch-thick fireproofing was perfectly
safe for a typical fire -- it met all the codes -- but it was not sufficient to withstand
what happened. After all, who would have designed a building to resist a fire like
that? (The possibility that faulty fireproofing that had gone unrepaired may have
been a factor in the collapse is being reviewed.)
On September 11, because the planes weren't slowed sufficiently by the exterior
walls, they penetrated the core. And when the planes broke through the gypsum
Sheetrock, the jet fuel poured into the core, he says. Two things happened.
Because of gravity, the fire went down the core. And because of the wind drafts in
the shaft, the fire also went up.
What can be done? How can future skyscrapers be designed to mitigate the dangers?
Kohn points to some of the design features in his firm's plans for the Shanghai
World Financial Center as examples of what is available to architects. We have to
look at the way buildings are being built in places other than the United States to
see what we can learn that might in the future reduce damage and death, he says.
These aren't things our firm takes credit for. The Chinese building code requires
them. As architects, before September 11, we thought they were overly conservative.
But in reality, the building would have stood a better chance against the 767
because of its structure and fire systems. There's of course no way to test it to be
sure, and we hope we never have to. Those features include a reinforced-concrete
core, special elevators for firefighters, refuge floors located throughout the
building and pressurized vestibules leading to fire stairs.
First, there's the core. The Shanghai skyscraper will have a concrete core
reinforced by steel rods. The narrowest point is two feet of concrete, he says,
the widest is four feet thick. A four-foot-thick concrete wall, he says, has a
much better chance of survival than Sheetrock, a better chance of resisting the
impact of a jetliner and preventing the jet fuel from igniting to the core and
spreading up and down the building. I think a four-foot reinforced-concrete core
could have withstood the impact and stopped the plane, particularly if the exterior
structure slowed the jet down sufficiently. Sheetrock couldn't stop it, even if the
jet had been slowed down.
The two Petronas Towers, as well as many other buildings, also have concrete cores,
and according to an article in The New York Times, architects and engineers agree
that if the World Trade Center had had a concrete core, the core might have stayed
intact in the crashes and offered a better chance of escape than the center's
gypsum-walled stairs.
When it comes to slowing a speeding jetliner, concrete is the key. Skyscrapers are
built primarily of steel and concrete; concrete can carry more weight, steel can
bend without breaking. After September 11, in a New York Times article on defending
skyscrapers against terrorism, architects and engineers said that to make a building
less vulnerable, reinforced concrete is superior and can better absorb the force of
a crash or an explosion. Concrete, though, is much heavier than steel, and when the
Trade Center was built, it was not a real option because huge pillars would have
been needed to hold the weight of the towers. Now, however, with advanced
technology, higher-strength concrete is available, and architects say it is being
used more.
But Kohn says that using too much concrete also has its problems. You could put
giant piers or columns in a building and make it more like a medieval fortress, but
the more you do to stop the plane from getting in, the less you are able to see out
of the building, and you begin to wonder why you would even build a super-tall
building that had no views. You could have big columns every four or five feet, and
glass maybe only 18 inches wide, and that starts not to make a lot of sense, in
terms of the building's function and appeal.
The compromise answer was suggested to him by the World Trade Center's original
engineers: architects should find ways to design the columns in the exterior walls
not to try to prevent a giant jet from penetrating the building, but to slow it down
and keep it from destroying the core. Obviously, the bigger the planes, the more
difficult it will be. Larger jets, like 747s and A-320s, or even bigger ones of the
future, could cause even greater damage.
But, he says, the bottom line is a building's design shouldn't be the first barrier
of defense against an attack from a jet, from unnatural forces. The responsibility
for defending against such an attack lies elsewhere.
A second fire safety feature of the Shanghai World Financial Center, one that is
required throughout Europe as well as in China, Japan and other parts of Asia, he
says, is firemen's lifts.
Firemen's lifts are fireproof elevators in the core of the building that have their
own power and their own pressurization and are reserved only for the use of firemen
in the case of a fire, Kohn says. They are big enough to carry injured people on
stretchers, in addition to firemen and all their equipment. So the firemen [are]
able to reach the fire within minutes without going up stairs. In the Trade Center,
the firemen -- 343 of whom were lost in the buildings' collapse -- had to climb the fire
stairs with their heavy clothes and equipment. By the time they got to the 40th
floor, they must have been exhausted, he says. And people were coming down,
escaping the fire, and they all met on the stairs. And of course, people going up
and down those stairs at the same time is not good. With firemen's lifts, the
firemen would have had unimpeded access to the fire. Whether they could have
controlled it or not will never be known, but with special foam to fight fuel fires,
which already exists, he says they would have had a shot.
Building firemen's lifts in cores means that the cores would have to be bigger. And
that means the buildings would be less efficient -- space would be given up for
something that would never be used except in an emergency. There's less space
available for the owner to rent out, and that reduces potential income from the
building, Kohn says. In this country, the attempt has been to maximize the usable
space and minimize the non-rental area.
Another crucial feature for Americans to consider, one that is required in China and
Hong Kong -- and one that would even further reduce the usable space -- is the refuge
floor.
They are absolutely isolated, absolutely fireproof floors with nothing on them,
nothing that can burn, only the concrete structure and mechanical equipment if it is
fireproofed. They are floors where people can assemble safely in the case of a fire.
In China there must be a refuge floor every 13 floors. They are connected by fire
stairs within the core, and these refuge floors become barriers, like a compartment,
sectioned off in a crisis.
The refuge floors are not designed specifically to contain a fire. What they do
allow is for an orderly evacuation, Kohn says. The refuge floors have individual
air systems and communications. No building is designed to evacuate 100 percent of
its population at one time. In order to do that, the fire stairs would have to be
humongous. What happens is, if you're on the 95th floor and there's a refuge floor
on 90, you wait on 90 until you are told to go to the next one. In this way, the
fireproof stairwells in the core would not become clogged and chaotic, and even if
the fire could not be controlled, if rescuers had at least two hours they could
evacuate the entire building.
In Hong Kong, refuge floors are required every 25 floors. That's probably more
sensible in the United States, he says. It's less conservative than the China
code, but both could be looked at to see which makes more sense in line with the
cost of the building. And perhaps the city would say it won't count the refuge floor
as usable space, so developers could build
additional usable space to make up for it, so they feel more comfortable building
refuge floors.
Another safety device, Kohn says, is the floor partition. In China, buildings have
partitions in the ceilings that are rated to withstand a fire for two hours. If
there's a fire or smoke, the partitions come down and seal off the floor in two,
three or four sections, depending on the size of the floor. A 40,000-square-foot
floor, like those at the World Trade Center, would have had a partition to split it
in half. Because of the heat of the fuel fire, the partition might have lasted for
only an hour or an hour and a half, but it might have allowed people to get through,
except on the floors where the jet went through.
An additional way to maximize fire safety, Kohn says, is to have pressurized
vestibules leading to fire stairs. Usually if there's a fire and you go to the fire
stairs, the smoke will come right in with you when you open the door, and with a lot
of people trying to get in, the door stays open. In most of the countries where we
work, pressurized vestibules lead to the stairs. The door to the vestibule closes
before you open the door to the fire stairs, and less smoke gets through.
There are also, especially in Japan, refuge areas on each floor -- fireproof corridors,
20 to 30 feet long, built to withstand a fire for at least two hours, where people
can congregate while waiting to get into the fire stairs. There may be a jam, he
says, and quite a few people can be protected while waiting their turn, which can
prevent panic.
Building and fire codes in America are really quite safe, Kohn says, and in a
typical 50- or 60-story building it's not necessary to do all of these things, but
when it comes to super skyscrapers and super disasters, some of them, particularly
the pressurized vestibules and the firemen's lifts, are worth a serious look.
In terms of design and function, the Shanghai World Financial Center is also worth a
serious look. William Pedersen, also a co-founding partner of Kohn Pedersen Fox, is
the design leader, working with Kohn and a third partner, Paul Katz, on the sleek,
dark tower, which has one instantly iconic, immediately recognizable feature: a
large circular hole, 50 meters (more than 164 feet) in diameter near the top.
The circle serves several purposes, Kohn says. The first is that the wind in
Shanghai is horrendous, and most of the wind problem
is relieved through the hole, which helps to keep the building structurally
economical. The second is that we wanted a very modern building, without spires and
pyramids and domes. The image of the building really comes from that circle. And the
third is that the circle represents the moon gate in Chinese mythology. The building
is square at its base, and in Chinese mythology the earth is square and the sky is
round. A circle also expresses the concept of unity.
The building will be 1,509 feet tall and the exterior will be built of glass.
Construction is expected to begin late this year or in early 2003 and be completed
by 2007, prior to the 2008 Summer Olympics in Beijing.
The site, located across the street from the Shanghai stock market, is expected to
contain mostly offices, although almost 1 million square feet of space at the base
will be available for stores. Above the offices will be a small luxury boutique
hotel, with about 100 rooms, mostly for businessmen who frequent the stock market
area.
At the top, at the base of the circle, will be an enclosed promenade for sightseers
to get wonderful views of China, Kohn says. Just below the promenade will be
restaurants, galleries and shops. And at this point, [Toyko-based] Mori [Building
Co.] is thinking about building, around the circle, an enclosed Ferris wheel ride.
It would be a spectacular ride, and we imagine people will wait in line for a long
time to get on it.
The idea is for the building to be the image of the new Shanghai, he said. The
plan was to design a very tall building, and the mayor of Shanghai says, 'Let's make
it the tallest.' The hope is to make Shanghai the leading financial city in Asia,
and to make this building its icon.
A. Eugene Kohn knew from an early age that he wanted to be an architect. He was born
in Philadelphia in 1930 and attended the University of Pennsylvania, earning an
undergraduate degree in architecture. After serving in the Navy as an officer for
eight years, including three on active duty during the Korean War, he returned to
the university, getting a master's in architecture. He worked first in Philadelphia
and then in New York, where he, Pedersen and Sheldon Fox co-founded what was to
become their highly successful firm.
Today, it employs about 400 people in its offices in New York and London. The firm
has designed buildings in more than 30 countries, including the Procter & Gamble
headquarters in Cincinnati, IBM headquarters in Armonk, New York, U.S.A. Today's
headquarters in Tysons Corner, Virginia, the new Baruch College campus in Manhattan,
and the new 5 Times Square building in Manhattan for Boston Properties and Ernst
& Young.
Kohn says he firmly believes that skyscrapers are good for cities. Many fellow
architects agree. Cesar Pelli, the architect of the Petronas Towers, told The New
York Times in an article published eight days after the trade center attack that
the desire to reach for the sky runs very deep in our human psyche.
Pelli added that he thought it was likely there would be a slowdown for a while in
the pursuit of very tall buildings. And David M. Childs of Skidmore, Owings &
Merrill LLP, architects of the third- and fourth-tallest buildings -- the Sears Tower
in Chicago and the
Jin Mao Building in Shanghai -- told the Times he didn't think tenants are immediately
going to want to be at the top of a tall building,
especially one that's an icon.
Robert F. Fox Jr. of Fox & Fowle, the architects of the 30-story Reuters
building at 3 Times Square, said in the Times that while a 30-story building makes a
lot of sense, the 100-story building never made sense. The vertical transportation
never works well. It strains all kinds of physics.''
But to Kohn, a skyscraper makes a lot of sense. For one, in places like
New York, Chicago, Hong Kong and Shanghai, it recognizes land value, it
recognizes density. When you have a lot of people -- Shanghai has 14 million -- there
isn't that much space to build on. You've got to build tall. Tall buildings are also
related to efficient transportation -- you can pack a lot of people in an area served
by public transportation. A critic in Boston says that from now on we have to build
like Paris: no more tall buildings. Paris is great, of course, but they put all
their tall buildings on the outskirts, in places like La Défense. If you want the
vibrancy of a city like New York, you have to build tall. From an environmental,
energy and open-space point of view, the tall building is wonderful. It's an
efficient concept.
He acknowledges that people, especially in the United States, may be reluctant these
days to build and work in super-tall buildings. Even before September 11, there was
no need in America to build a new super skyscraper, 80 stories or higher. The
failing economy didn't call for it and the real estate market didn't call for it.
The cost is so high, and unless there's a fantastic site and a healthy market, it
won't work. So we weren't going to build one for at least 10 years. And people I've
spoken to who escaped from the trade towers say they will never go back into a
super-tall building.
But my concern is that because of the terrorists, we will overreact and do all the
wrong things. If we start to build fortresses, if we don't enjoy our cities, if the
major corporations relocate from the city out to the vast countryside and build
large, low campuses and put fences and guards around them, and if we start to see
the cities degenerating as a result, it would be a vast overreaction, and a great
pity.
Above all, he says, we as a civilization should not be afraid.
Mervyn Rothstein is an editor at The New York Times and a frequent
contributor to Cigar Aficionado.
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