Wind engineering for green buildings
ASSESSING vertical wind profiles and turbulence intensity in areas affected by wind events was conducted for the Burj Dubai soon to be the world’s tallest building.rwdi.com
AS ARCHITECTS become bolder in the design and shape of buildings, and building owners want taller buildings, there is a need for wind engineering.
What is wind engineering?
The interaction of the environment with the architectural and structural features of a building is now the subject of a specialty field of engineering. There are now engineering consultancy firms that address all aspects of wind and climatic effects on buildings.
Developers, owners and architects now consider wind impact on buildings and pedestrians below.
Wind control features are now considered in the design of buildings and bridges.
Office and residential towers are shaped and oriented according to the local wind environment. The influence of surrounding buildings on local wind patterns is studied when designing a new tall building.
Higher buildings, longer bridges and more daring structures have to be designed to withstand gale winds and strong earthquakes.
Taipei 101’s unique feature for example, is its steel pendulum weighing 660 metric tons suspended from the 92nd to the 88th floor. This pendulum serves as a tuned mass damper as it sways to counter the building’s sideways movements caused by strong gusts of wind.
A group of Canadian consulting engineers was in town to feature finished projects using very sophisticated wind engineering technology.
The RWDI with 14 offices worldwide was consulted for projects such as Kuala Lumpur International Airport and Petronas Towers, Taipei’s 101, Dubai’s soon to be the world’s tallest building, Burj Dubai. The company has done wind engineering and microclimate consulting projects in America, Europe, China and India.
Wind tunnel test
For the cost of around US$40,000 to US$60,000, they can do a wind tunnel test for a proposed 30-story building in two months at the longest. To get structural wind loading information so that the design of foundation and structural framing can proceed, they would need geometric informa tion and structural characteristics including natural frequencies, mode shapes and mass distribution.
Wind loads provided in codes and standards are based on building shapes of 40 years ago. The codes are updated yet they are general in nature.
The effect of turbulence due to neighboring structures or terrain features is not in the codes. Today’s high-tech building materials and design methodology creates a complex situation that needs wind engineering consultants to optimize cost and safety of the project.
The wind tunnel test facility includes appropriate instrumentation and data acquisition to create a building’s model in which ground roughness and turbulence generators simulate the natural drag on the wind flowing over it. Change in wind speed and gustiness is measured as wind approaches the project.
Pressures and suctions caused by the wind are evaluated so that pressure locations are measured hundreds of times. Measurements are generally made for 36 wind directions in 10-degree increments. This results in recommended loads in the structural design and block diagrams of wind pressures showing pressure zones around the surface of the building.
Pedestrians may not realize that low-rise terraces, trees and canopies dampen wind speeds along the sidewalks.
Inset floors above projecting floors reduce downwashing winds.
Balconies on tall buildings especially when facing the sea can have an impact in reducing wind loads, if well designed.
A building with sharp corners experiences high suctions and corner balconies can reduce peak suction by up to 30 percent.
Canopy shelters at ground level in malls, office and commercial buildings enhance pedestrian wind comfort.
Wind patterns are the reason for stepped, curved corners, and terraces on only one side of buildings.
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