NORMAL WIND PRESSURE 15 



Straight Line formulas are given in Fig. 6, for P equals 20, 30 and 

 40 pounds. 



It is interesting to note that Duchemin's formula with P equals 30 

 pounds gives practically the same values for roofs of ordinary inclina- 

 tion as is given by Hutton's and the Straight Line formulas with P 

 equals 40 pounds. 



Ducnemin 



Mutton 



Straight Line 



Straight Line &&*.& *45) 



Normal Pressure,!bs-per sq ft- 

 P= Horizontal 

 A =/4ngle of inclination of surface 



10 15 2O 5 30 35 4O 45 50. 55 6O 65 70 75 60 



Angle Exposec) Roof mokes with Horizontal in Degrees, A- 



FIG. 6. NORMAL WIND LOAD ON ROOF ACCORDING TO DIFFERENT 



FORMULAS. 



Duchemin has also deduced the formula 



2 sin 2 A 



P h =P 



(7) 



sin 2 A 



where P h in (7) equals the pressure parallel to the direction of the 

 wind, Fig. 5; and 



5 2 sin A cos A (8) 



Pi 



1 4- sin 2 A 



