84 



LOADS IN STRUCTURES 



All necessary data for calculating the wind pressure on a 

 roof with any one of the customary pitches and a horizon- 

 tal wind pressure of 40 Ib. per sq. ft. are given in the 

 table on page 83. 



The diagram shown in Fig. 2 facilitates the finding of the 

 normal pressure p for the usual slopes and for horizontal 

 wind pressures of 20, 30, and 40 Ib. per sq. ft. 



70 



I Pitch 

 90 



i Pitch 

 jPitch 



| SO" 



/ Pitch 



I 



$i Pitch 

 8 30 

 ^i Pitch 



" 



1O IS 2O 26 3S 



Wind Pressure Formal to Slope of Roof in Pound* Per Square Fobt 



FIG. 2 



The values of the normal pressure for a given slope and a 

 horizontal wind pressure of 20, 30, or 40 Ib. may be found 

 as follows: Assume that the normal pressures on a roof hav- 

 ing an angle with the horizontal of 40 is to be determined. 

 Proceed along the horizontal line marked 40 until it inter- 

 sects the curve marked 20 Ib., which represents a horizontal 

 wind pressure of 20 Ib. The point of intersection indicates 

 the normal pressure p, the value of which is found by draw- 

 ing an imaginary vertical line to the base line, which is 

 marked off in pounds of pressure per square foot. It is 





