12 <>TESO.\ PLATE-GIRDER DESIGN 



part of its length a formula for the safe compressive 

 and unit >\.reaa 



P- 16,000 -20o, ..... (2') 



may be used. 



Experience has shown that no material should be 

 used which is less in thickness than ^ of the distance 

 between the rivets in the direction of the action of the 

 stress, J of the distance from the center of a rivet to tin- 

 edge of the piece at right angles to the line of stress, or 

 that any angle leg when used alone in a girder flange shall 

 he longer than 12 times its thickness, otherwise the girder 

 flange may fail in detail rather than as a whole. 



For simplicity and ease of construction the compres.-ion 

 flange should not be made of greater section than the 

 tension flange, therefore the compression flange must be 

 supported in a sidewise direction at frequent intervals, which, 

 from the pin. ding formula, will be about every ten times 

 the flange width. It is customary to consider that the 

 rivets completely fill the rivet holes in the compression 

 flange and that the full gross section of the flange may 

 be assumed to act to resist compression. This assump- 

 tion with regard to the rivets always filling the holes is 

 open to serious question, and if they do fill the holes 

 they do not offer the same resistance to lateral deforma- 

 tion which takes place under compression as the unpunched 

 rial. However, it is fair to assume that they partially 

 make up the punched-out material. The formula for the 

 unit stress for the compression flange is believed to be 

 nough to allow it to be applied to the gross area 



