What is the effect of Exposure B on wind pressure?

What is the effect of Exposure B on wind pressure?

• A. Wind accelerates, resulting in higher wind pressures
• B. Wind is slowed by obstructions, resulting in lower wind pressure
• C. Wind has highest pressures due to flat, unobstructed areas
• D. Wind pressure is unaffected by obstructions

Answer: (B)

Wind pressure depends on how fast the wind is moving at the height of the structure, and it grows with the square of that speed. Exposure B represents an area with obstructions such as buildings and trees near the surface, which roughen the ground and slow the wind before it reaches the structure. Because the velocity is reduced, the dynamic pressure on the roof or walls drops accordingly (since pressure ∝ velocity^2). So, Exposure B leads to lower wind pressures compared to open, unobstructed areas. The idea that wind would accelerate, or that pressures would be highest in flat, unobstructed spaces, or that wind pressure is unaffected by obstructions, doesn’t fit how roughness and obstructions actually diminish wind speed and thus wind pressure.

Wind pressure depends on how fast the wind is moving at the height of the structure, and it grows with the square of that speed. Exposure B represents an area with obstructions such as buildings and trees near the surface, which roughen the ground and slow the wind before it reaches the structure. Because the velocity is reduced, the dynamic pressure on the roof or walls drops accordingly (since pressure ∝ velocity^2). So, Exposure B leads to lower wind pressures compared to open, unobstructed areas. The idea that wind would accelerate, or that pressures would be highest in flat, unobstructed spaces, or that wind pressure is unaffected by obstructions, doesn’t fit how roughness and obstructions actually diminish wind speed and thus wind pressure.