10 3 ON PLATE-GIRDER DESIGN 



passing through the space marked /) are considerably 



U-iil and thereby increased, and therefore the distance /> 

 for a good stagger for this case should be ;*". It should 

 be noted that most girders have an excess of strength 

 t at the point of maximum bending moment and 

 at t! of cover plates, and hence care in staggering 



the rivet* need only be exercised at these points. 



The entire flange stress is developed in small incre- 

 ments by the web and transmitted to the flange by the 

 rows of rivets connecting the vertical legs of the angles 

 to the web. It is dear that these angles then should 

 comprise a considerable part of the total flange a 

 some engineers require 50%, other* permit as little as 

 33J',. The irinler which has a flange stress developed 

 in a short distance require* heavier angles than one in 

 which tl B i* developed in a great distance. The 



>in^ provision for maintaining net section applies par- 

 ticularly to the tension flange. The compression flange 

 is usually made equal in gross area to the tension flange. 



The compression flange is in somewhat the condition 

 of a column as far as liability to failure in a sidcwise 

 din-etion is concerned. For girders with a constant top 

 flange section the maximum unit stress occurs only at the 

 point of maximum moment, for a flange with cover plates; 

 that is, for a flange which varies closely as the flange stress, 

 the unit stress is nearly constant throughout. The web 

 stiffeners. if any are used, give considerable lateral still- 

 ness to the top flange, reaching and connecting, as they do 

 for half their length to material in tension. The sketch of 

 Fig. 3e will lu-lp make this point clear. The tension flange 



