DESIGNING. 213 



supply pipe, of required diameter, should be connected to the 

 bottom at its lowest point by means of a standard expansion- 

 joint. 



Stress and Section of Tower Members. The determination 

 of the stress produced in the tower by the action of the wind is 

 arrived at as follows: 



Taking wind in direction of the diagonal as shown by arrow 



W (Fig. A), the maximum tension is produced in column A and 



the maximum compression in C; therefore, taking moments 



"about mn, WH or M=V a X sin 45+ V C X sin 45; and as 



V a =V C3 therefore 



M M 



This vertical force (V a ) is resolved into its components, a 

 force downward through the columns and the horizontal force, 

 which is in turn resolved into Jtwo forces lying in the planes of 

 the trusses AB and AD. The same is true of V e at column C, 

 hence tension in A is 5= V a sec0, being angle of inclination of 

 post. Compression in C is the same as tension in A. 



The horizontal force then is h = V a tan 0, and its components 

 in the sides of the tower marked R (Fig. B) are 



R = h sin 45, 



R= V a tan/? (.707). 



W 



Having the shear at the top of each post, which is , acting 



4 



in the same direction as the wind, this must be resolved into 

 forces lying in the planes of the sides of the tower. These are 



equal to P = sin 45 = (.707) acting in direction shown by 

 4 4 



arrows P (Fig. C). 



These forces must be combined with the forces R, and this 

 combination is shown in Fig. D. 



