TOWERS AND TANKS fOR WATER-WORKS. 



vals. These latter should always be less than the depth of the 

 girder. . . . Stiffeners should always be used at or near the sup- 

 ports, and at any point where there is a concentration of heavy 

 loads. 



" The duty of these stiffeners in such cases is twofold: first, 

 to prevent buckling of the web; second, to transmit the shear 

 to the web by means of abutting areas and the rivets, both of 

 which must be sufficient for the purpose." 



There has not to this time been formulated any rational 

 theory for either the spacing or size of stiffeners in plate 

 girders, although it has erroneously been assumed that when 

 stiffeners are introduced at intervals not exceeding the depth 

 of the girder, the conditions are analogous to those of a 

 truss composed of posts and tension members and to the 

 solution of which the Gordon or other compression formula 

 might be applied. As a matter of fact, both size and spacing 

 of vertical stiffeners are largely matters cf judgment and are 

 governed by the usual practice for particular cases. Allowable 

 flange strains are usually taken as 15,000 pounds. The rivets 

 generally used are J-inch, spaced not more than 6 inches and 

 closer than this for heavy flanges. Where loads are great, es- 

 pecial calculation for rivet-spacing should be made, allowing 

 9000 pounds per square inch for shearing and 18,000 pounds 

 per square inch for bearing. The unsupported width of flange- 

 plates subject to compression should not exceed 32 times their 

 thickness, nor should the flange-plates extend beyond the outer 

 line of rivets more than 5 inches nor more than 8 times their 

 thickness. The term "flange" as applied to riveted girders 

 embraces all the metrJ. in top cr bottom of girder exclusive of 

 web plate; or in the case of a rolled beam or channel with top 

 and bottom plates, all metal exclusive of that part of the web 

 between fillets. With a circular girder as with a simple beam, 

 il;s ability to support a load depends upon the strength and ar- 

 rangement of its fibres, limited by the distance between 'supports. 



