GIRDERS AND TRUSSES 115 



care of the shear, this being accomplished by using the following 

 formula : 



rd 

 9- T 



in which V = total vertical shear at the section considered, 

 r = the resistance of one rivet, 

 d = distance in inches between the center of the upper 



row of rivets and the lower row of rivets, 

 p = pitch, center to center of rivets, in the flange. 

 The bending moment due to uniform load varies as a parabola, 

 and as plate girders are generally designed for a uniform load the 

 cover plates are varied in length to provide enough area for ten- 

 sion or compression. They extend a short distance past the point 

 where they are no longer required, to allow for proper connec- 

 tions. By having the plates stop when no longer required some 

 weight is saved and the design is the most economical possible. 

 When concentrated loads must be cared for in addition to a uniform 

 load the process is altered. 

 Let A - total area of angles and cover plates in one flange at 



mid-span, 



aj - area of shortest cover plate, 

 a = area of second cover plate, 



Ox - area of longest plate, the plates being numbered pro- 

 gressively from 1 to the end, x being used to signify 

 any general terminating number. 



Similarly li, h . . . l n , etc. = lengths of the plates, the letter 

 n being used to designate the general number applying to the last 

 plate, thus l n = length of the last plate considered. 



L 



then, In - ~T X \/ai + a s + . . . a,. 



The angles always extend the full length of the web plate. 



In spacing rivets hi the flanges of plate girders it is common 

 practice to have the rivet spacing uniform between stiffeners, the 

 amount of vertical shear considered as being taken at each stif- 

 fener. The minimum distance between centers of rivets is three 

 diameters of the rivet, but not less than 3 ins. for |-in. rivets and 

 2 ins. for f-in. rivets. In the flanges the maximum pitch should 

 not exceed six times the diameter of the rivets. The maximum 

 pitch at ends of cover plates should not exceed four diameters of 

 the rivets for a length equal to twice the depth of the girder. The 



