What is the wind behavior in Exposure B?

What is the wind behavior in Exposure B?

• A. Wind is slowed by obstructions, resulting in lower wind pressures.
• B. Wind speeds are increased by obstructions.
• C. Wind is unaffected by obstructions.
• D. Wind direction becomes more erratic due to obstructions.

Answer: (A)

Exposure B represents wind in areas with moderate surrounding obstructions, like a typical city or suburban neighborhood. The presence of buildings and trees slows the wind flow at the site, so the mean wind speed at the structure’s height is reduced compared to open areas. Since wind pressure scales with the velocity squared, this slower wind produces lower design wind pressures on the structure. The idea is that shielding by obstructions lowers both the wind speed and the resulting pressures. This is why the correct description is that wind is slowed by obstructions, resulting in lower wind pressures. The other options contradict the shielding effect—obstructions do not increase speeds, they do not leave wind unchanged, and while obstructions can cause turbulence, the defining behavior for Exposure B is the reduction in wind speed and pressure due to shielding.

Exposure B represents wind in areas with moderate surrounding obstructions, like a typical city or suburban neighborhood. The presence of buildings and trees slows the wind flow at the site, so the mean wind speed at the structure’s height is reduced compared to open areas. Since wind pressure scales with the velocity squared, this slower wind produces lower design wind pressures on the structure. The idea is that shielding by obstructions lowers both the wind speed and the resulting pressures. This is why the correct description is that wind is slowed by obstructions, resulting in lower wind pressures. The other options contradict the shielding effect—obstructions do not increase speeds, they do not leave wind unchanged, and while obstructions can cause turbulence, the defining behavior for Exposure B is the reduction in wind speed and pressure due to shielding.