230 



PRACTICAL STRUCTURAL DESIGN 



to scale the amount of the wind force. At the left end, Ri, lay 

 off the length cd, equal to ab. Connect the right end, R 2 , to d 

 with a straight line, intersecting ab in e. Then the length ae 



Fig. 151. Wind on Roof with Ends Fast. 



represents the left reaction and the length be represents the 

 right reaction. The wind is assumed to be blowing from the 

 left, but, for this case, the members are dimensioned to be strong 

 enough to resist the wind from either side. The reactions will 

 then in amount be equal to the larger reaction. At (6) is shown 

 the force diagram for the wind. 



In Fig. 152 is shown a method for computing the reactions 

 when both ends of the roof are fast (secured). The reaction 

 lines are drawn parallel to the wind resultant. The wind acts 



at the center of one 

 side of the roof. The 

 distances x and y are 

 measured normal to 

 the resultant. Mul- 

 tiply the wind by the 

 length y and divide by 

 the length x. This 

 gives RZ, which is 

 subtracted from the 

 total wind force to 

 Fig. 152. Inclined Reactions from Wind. obtain Ri. The prob- 

 lem is seen to be that of a beam carrying a single concentrated 

 load. 



