304 TOWERS AND TANKS FOR WATER-WORKS. 



when computed by a recognized formula, with proper allowance 

 for decreased resistance after punching and riveting, but no 

 plate shall be less than one-quarter (J) inch thick. 



Rivets shall be provided to resist the entire stresses trans- 

 mitted, and shall be of sufficient size and number to present ample 

 resistance to shearing and afford bearing area sufficient to 

 prevent the liability of crushing the metal about the rivet-holes. 

 The bearing value of rivets shall be assumed at .not less than 

 twelve thousand (12,000) pounds per square inch when the area 

 considered is the diameter of the rivet-hole multiplied by the 

 thickness of the metal. The pitch of the rivets shall equal the 

 net section of plate. The ratio of the strength of the riveted 

 joint to that of the solid plate shall not be less than the 

 following : 



Single-riveted joint 56% 



Double-riveted joint 70% 



Triple-riveted joint 75% 



Double-riveted butt- welt joint 87% 



Tensile and shearing strains on rods and pins shall not exceed 

 twelve thousand (12,000) pounds, and bending strains shall not 

 exceed twenty-five thousand (25,000) pounds per square inch 

 when the centre of bearings of the strained members are taken 

 as the points of application of these stresses. 



The stress in the circular girder shall be assumed as due to 

 the entire weight supported and the resultant horizontal thrust 

 at the top of the posts. The shear strain on the girder and the 

 horizontal thrust on the lower flange ring shall not exceed ten 

 thousand (10,000) pounds per square inch of metal. 



The cover shall be designed to safely resist the assumed wind 

 stress, but no cover-plate shall be less than three-sixteenths (3/16) 

 inch thick, and shall be rein forced- when necessary by radial 

 rafters, tie-rods, or otherwise. 



