82 



LOADS IN STRUCTURES 



determined that the pressure per square foot on a vertical 

 surface is approximately represented by the formula 



p = . 00492V 2 , 



in which p is the pressure, in pounds per square foot, of ver- 

 tical surface, and V is the velocity of wind, in miles per hour. 



Careful records, extending over a period of years, show 

 that the velocity of the wind seldom attains 100 mi. per hr. 

 probably not more than once in the lifetime of a structure. 



The following table was calculated by means of the pre- 

 ceding formula. Though the table indicates that for 100 mi. 

 an hr. the pressure per square foot is nearly 50 lb., modern 

 practice often allows only 40 lb. per sq. ft. for large surfaces. 



VELOCITY AND FORCE OF WIND, IN POUNDS PER 

 SQUARE FOOT, ON A VERTICAL SURFACE 



Curved and flat surfaces not in a vertical plane are sub- 

 jected to less pressure than flat vertical surfaces. The pres- 



