DESIGN OF PLATE GIRDERS 223 



than given by the formula allowed shearing stress = 12,500 90 H f 

 where H = ratio of depth to thickness of web plate, the stiffeners will 

 be near enough together. Where the shearing stress is less than given 

 by the above formula, stiffeners may be omitted or spaced as desired. 



Stiffeners are commonly designed as columns, free to move in a di- 

 rection at right angles to the web, with an allowed stress P = 12,000 

 55 / -f- r. Stiffeners should be provided at all points of support and un- 

 der all concentrated loads, and should contain enough rivets to transfer 

 the vertical shear. 



Web Splice. In the plain web splice shown in Fig. 108, the rivets 

 take a uniform shear equal to S ~- n, where $ is total shear, and n 

 is number of rivets on one side of splice, and a shear due to the shearing 

 stress not being applied at the center of gravity of the rivets. This is 

 the problem of the eccentric riveted connection, which has been dis- 

 cussed in Chapter XV. 



If the web is assumed to take part of the bending moment there 

 will be an additional shear due to bending moment. 



Rivets in the Flanges. In Fig. 108, let $ = the shear in the girder 

 at the given section, h' = distance between rivet lines, p = the pitch of 

 the rivets, and r = the resistance of one rivet (r is usually the safe 

 bearing on the rivet in the web). 



Then taking moments about the lower right hand rivet, we have 



Sp = rh', and p = rh' -*- 5 (81) 



Where the rivets are in double rows as shown in (d), the distance 

 h' is taken as a mean of the distances for the two lines. 



The crane loads produce an additional shear in the rivets, (e) Fig. 

 108, which will now be investigated. We will assume that the rail dis- 

 tributes the load over a distance of 25 inches ; this distance will be less 

 for light rails and more for heavy rails. The maximum vertical shear 

 on one rivet will- be Pp -f- 25 = 0.04 Pp. The horizontal stress due to 

 bending moment is r = Sp -=- h' t and the resultant stress from the two 

 sources will be 



