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A Roof That Withstands Wind and Snow
May 31, 2012   
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A wind tunnel in Cracow’s Czyżyny district—operated by the Institute of Structural Mechanics at the Cracow University of Technology’s Faculty of Civil Engineering—is the only facility of its kind in Poland that conducts simulations to examine the impact of wind on a roof covered with snow.

A wind tunnel is a facility used in aerodynamic research to study the effects of air moving past solid objects. Aircraft and vehicles are tested in wind tunnels. In addition, wind tunnels are used to study the airflow around large structures such as bridges or buildings.

Just how dangerous snow lying on the roof of a building can prove to be was shown by a tragedy in the Polish southern city of Katowice, Silesia province, in 2006 when the roof of an exhibition hall suddenly collapsed, killing 67 exhibitors and visitors and injuring 140. The whole structure came down in a matter of seconds.

After that disaster, the Cracow University of Technology’s Wind Engineering Laboratory began researching roofs in terms of what kind of loads they can bear.

The Cracow wind tunnel, officially called the Wind Engineering Laboratory, was launched 11 years ago to examine the influence of wind and temperature on various structures. Following the Katowice disaster, the laboratory also began examining the impact of snow and ice on facilities.

The lab carried out simulations for a new sports stadium in Poznań that has been built for the Euro 2012 soccer tournament. The laboratory examined the strength of the stadium’s roof. According to the lab’s manager, Prof. Andrzej Flaga, the aim was to determine the distribution of wind pressure on different parts of the roof structure. On the basis of the measurements made in the laboratory, the researchers established the wind patterns and passed this data on to the stadium designers so that they could use them in their calculations of the structure’s durability.

The aerodynamic tests of the Poznań stadium were commissioned from the lab by the chief designer of the stadium, the Modern Construction Systems company. The lab’s staff, while measuring the impact of wind, also conducted simulations in the wind tunnel of the impact of snow using a model of the stadium scaled 1 to 200. This complex study, which involved measurements of the thickness of snow cover using the photogrammetric method, was performed in Poland for the first time, according to Flaga.

The lab is preparing for further projects involving a stadium in Tarnów and a sports-and-entertainment arena in Cracow.

The Cracow wind tunnel stands on a high foundation and resembles a huge aquarium with a suspended ceiling. It is 10 m in length, 2.2 m in width, and more than 1.5 m in height. Inside are fans, diffusers and other sophisticated equipment designed for measuring aerodynamic forces.

The purpose of the simulations in the tunnel is to determine the basic aerodynamic properties of various facilities. Investors planning architectural projects want to be sure that their skyscraper, building, bridge or roof will not collapse under the impact of wind or the weight of snow. They consult the Cracow scientists before they decide to go ahead with their projects.

One of the biggest challenges for the lab was aerodynamic research involving a 225-meter skyscraper planned in the southwestern city of Wrocław. This would be the tallest high-rise nationwide—an elliptical structure without a right angle and with a complex roof. The impact of wind on a model of that building has been tested in the tunnel.

The lab’s services are used by architects, urban planners, ventilation system experts, engineers, and constructors. The facility also serves students who can conduct basic research here involving measurements of airflow, wind pressure, aerodynamic forces, and vibrations.

Teresa Bętkowska
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