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"New York has the worst wind in the nation," says Robertson. "Tall buildings are designed to withstand earthquakes, temperatures and even the constant pelting of rain, but wind remains the peskiest." Speaking from the conference room of his third floor office at 211 East 46th Street, Robertson says that buildings can be tipped several inches by wind — called a "wind load" by engineers — and then oscillate five times that amount, swaying like a pin that has been grazed by a bowling ball. On an average day, for example, the World Trade Center sways about a foot between the windward and leeward sides, and takes about eight seconds to complete one rotation. "The building develops twisting and swaying," says Robertson. "So if you're in a corner office, there are even higher levels of acceleration." Which translates into a feeling akin to sea sickness. According to Robertson, New York City has some of the worst wind loads in the nation, even stronger than Chicago or Los Angeles. This is because of the occasional wind generated off of the Atlantic Ocean during hurricane season. As a result, buildings in New York City must be designed to be twice as strong as similar buildings designed to withstand an earthquake in Los Angeles.
 n
order to ensure the safety of a building design, tests are conducted
in long wind tunnels using miniature scale models of buildings —
just a couple feet tall — that are placed among other buildings
that mimic city contours. A giant propeller blows air into the tunnel
as a computer collects data from "pressure taps" connected to the
model buildings. The process is not as exciting as it may sound. "Wind
tunnel testing is like going to the submarine races," says Robertson.
"Incredibly dull."
Robertson says that the World Trade Center was the first ever skyscraper to be constructed using this type of "rational wind engineering." Prior to that, buildings were tested autonomously in aeronautical wind tunnels without other models, and as a result, did not predict wind effects accurately. "The aeronautical tunnels did not replicate the actual wind," says Robertson. What
makes the World Trade Center even more unique is that unlike other
skyscrapers, it doesn't taper as it rises. "It puts more real estate
higher up than any other building," says Robertson, adding that
there is actually more usable area in the top floors than the bottom
floors. In comparison, the top floors of the Sears Tower in Chicago
are one ninth the area of its base. "Having the space in the World
Trade Center is a huge advantage," says Robertson. "It's a high
rent district . The perimeter at the top is 800 feet. The Sears
tower has about a third as much."
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eslie Robertson
has been fighting wind for over 50 years. As a structural engineer
— now Director of Design for his own engineering consulting
company — Robertson has engineered buildings that are recognizable
the world over, such as the World Trade Center and the headquarters
for AT&T, now the Sony building. 
