114 PRACTICAL STRUCTURAL DESIGN 



Divide the load by a fiber stress of 12,500 Ibs. per square inch for 

 the area of the stiffeners and use fillers to keep the stiffeners 

 straight. 



The flange may be made solely of angles extending the whole 

 length of the web plate, or of angles with plates riveted to them, 

 the latter type being adopted when angles alone will not be suffi- 

 ciently strong. The plates seldom extend the full length and if 

 more than one flange plate is used the outer plates are very short, 

 the lengths increasing progressively as they get closer to the angles. 

 These plates are known as cover plates, and when different thick- 

 nesses are used the thinner plates are on the outside. 



The resisting moment is determined as follows: one-eighth 

 the area of the web is considered as forming part of the flange. 

 This is the usual custom, but some engineers use only T V and 

 some ^f. 



,, r , Rbd? 

 M r of web = 5 

 o 



6 = thickness of web plate. 

 d = total depth of plate. 



/ = unit fiber stress (usually 16,000 Ibs. per sq. in). 

 M r of angles = Adf. 



A = area in sq. ins. of the two angles on one edge of 



plate. 

 d = distance center to center of gravity of the 



angles on upper and lower edges of web 



plate. 



/ = unit fiber stress. 

 M r of cover plates = Adf. 



A = area in sq. in. of plates on one edge of web 



plate at middle of span. 

 d = distance center to center of gravity of cover 



plates. 

 / = unit fiber stress. 



The total moment of resistance of the plate girder is the sum 

 of the moments of resistance of the web, the angles, and the cover 

 plates. 



The rivets used to connect the flange angles to the web and to 

 connect the cover plates to the angles must be spaced to take 



