Wind Tunnel Helps Chicago Architectural Firm Test Designs
How Wind Tunnel Helps Architects
(CBS) -- Architects and engineers spend a lot of time designing modern high-rises so they can handle the kind of wind gusts Chicago has experienced in recent days.
Today's designs are tested in wind tunnels, but only one architectural firm in the world has its own -- and it is located in a historic building across the street from the Art Institute of Chicago.
The Skidmore, Owings & Merrill wind tunnel is 30 feet long, 40 inches wide and 55 inches tall, tucked away in a mezzanine office of the 111-year-old Railway Exchange Building, designed by a Daniel Burnham associate and once home to Burnham's architectural firm.
While the wind tunnel may seem small when stacked up against some of the world's tallest and most innovative buildings, Skidmore structural engineer Christian Hartz says it is large enough to test design characteristics of skyscraper models at 1/500 full size -- large and accurate enough for most testing.
"The air in the top moves faster than the air on the bottom and this airflow then hits the building (model)," he says.
Hartz said the model sits atop a load cell that generates the data designers use. It is positioned at the back end of the wind tunnel. The space in front has a Lego surface, to allow for the placement of other objects that can simulate the skyline surrounding the proposed building.
Skidmore structural engineer Bradley Young says the average test is not long. The wind tunnel "warms up" to a speed of 26 feet per second.
Young says the data are fed into a computer.
"With this data we then can actually calculate forces, movement, frequencies and all of the stuff that we need," Hartz says.
Until Skidmore built its tunnel, it had to "stand in line" with other architectural firms and work with commercial wind tunnels in Canada and London. While wind tunnels exist at local universities, Skidmore structural engineer Bradley Young says they are not ideally suited to producing the types of winds high rises encounter.
Hartz said the ability to use a tunnel in-house gives Skidmore an advantage when presenting design ideas.
"The earlier you have that, the better for you," he says. "We're trying to do this before we go the first time to the client. We've never shown anything to the client, and already we know that this shape is kind of good."
Hartz said that when using a commercial wind tunnel, it is difficult to do the needed testing on more than six to eight designs a day. The Skidmore tunnel is available to the firm's offices in Chicago, San Francisco, New York and London, and some design ideas can be refined and re-tested same day.
Skidmore still makes use of commercial wind tunnels, often to act as a "second opinion." Hartz and Young say there are occasional "surprises," but said the results usually mirror one another.
Wind tunnel testing of building designs is a relatively new art, first done 50 years ago during planning of Chicago's John Hancock Center, but Young said that today it is a must worldwide.
"The architectural shape of the building is the most important influencing factor in terms of mitigating or compounding wind effects," he says.
