# Calculate wind pressure

Jonathan Ochshorn

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Directions: Enter values for wind speed (mph); exposure category (B, C, or D); roof height (feet); importance factor (1.0 for normal buildings); plan dimensions, L and B (units in feet; see Fig. 1); Kd, the wind directionality factor (equal to 0.85 when multiple load types are being considered simultaneously, otherwise, 1.0); and Kt, the topography factor (equal to 1.0 for normal conditions, but may be higher for buildings on hills or escarpments). Press "update" button.

More detailed explanations and examples can be found in my text.

Fig. 1. Plan dimensions "L" and "B"

Fig. 2. Windward and leeward wind pressure

Wind pressure is deployed on the "windward" and "leeward" sides of the building as shown in Fig. 2. Note that (a) the windward pressure varies along the height of the building, while the leeward pressure is assumed to be constant; and that (b) the leeward pressure is negative, i.e., pulling rather than pushing on the building. As the windward and leeward pressures act in the same direction, the combined value is found by subtracting the negative leeward values from the positive windward values. Magnitudes of these wind pressures are tabulated below. Works for "rigid" rectangular buildings with flat roofs.

 city wind speed (mph) if 'other' wind speed used (mph) exposure roof height (ft) Importance Boston, MA Chicago, IL Little Rock, AR Houston, TX Ithaca, NY Los Angeles, CA Miami, FL New York, NY Philadelphia, PA Phoenix, AZ Portland, ME Other B C D I=low hazard II=normal III=high hazard IV=essential height above grade (ft) windward pressure (psf) leeward pressure (psf) combined pressure (psf) Kd Kt 1 0.85 L (ft) B (ft) Checks: errors: wind speed > 0 roof height > 0 roof height <= 500 L > 0 B > 0 1 <= Kt <= 3