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Name: Evie
Status: student
Grade: 9-12
Location: LA
Country: USA
Date: Summer 2011


Question:
How could you quantify and analyze the force of wind on a high rise building?



Replies:
With some difficulty! The force depends upon the details of the shape of the building, in all three directions. In addition, the force depends upon the wind profile, also in all three directions. In addition, there can be torques (twisting motions). There can also be resonances if the building and the wind interact with one another. While building engineers have to do these kinds of computations, they are neither simple nor easy.

Vince Calder


Hi Evie,

Manually calculating wind loading on a building (or any object) is an extremely complex and difficult task, and the results are usually not very accurate. These days, this task is accomplished using Finite Element Analysis (FEA) software running on a very fast computer. The results are quite accurate, but highly computation-intensive. This type of software does an initial calculation, then the answer is used to refine the next iteration of calculations. This is commonly repeated hundreds of times until the results converge on a solution that no longer changes with each repetition. Even on a fast computer, it can take many hours of calculations before the results converge on a solution.

To use this type of FEA software, a CAD model is first created using 3D modeling software such as SolidWorks, ProEngineer, or similar engineering software. Then the file containing the 3D computer model is fed into the FEA software referred to above. The results are impressively accurate.... vastly more accurate than is possible with manual calculations.

Regards,
Bob Wilson.


It is very difficult to actually measure the wind forces on a full-size high rise. Wind forces push and twist the entire building. A good measure of total wind forces can be obtained by putting force sensors on the outside walls that measure the wind pressure, and add up the measurements. Better accuracy is obtained when there is more force sensors.

A direct, but less practical way to determine the wind forces on the building is to first measure how far the building deflects (inches or fractions of an inch) in the wind, measured by sensitive instruments. If one knows mathematically the relationship between force and deflection then one can calculate the force, but this force-deflection relationship is also not easy to figure out either. Because of the difficulty in instrumenting an actual building, many researchers use miniature model buildings (a few feet tall). The miniature models are put into a wind tunnel for testing, where the wind can be controlled very well. These models have force sensors built into them and a lot can be learned this way. The only drawback to this method is that complicating effects (gusts, terrain, etc) on the smaller model may not exactly duplicate in miniature the wind forces on the full size building.

A fourth way to analyze the force on a building is to do a mathematical calculation on a computer. The science behind these calculations is quite well established, and accurate results can be obtained. It is good to verify the computer model using a miniature model in a wind tunnel, and best of all it is good to check these analyses using a real building.

Robert Erck



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