116 



PRACTICAL STRUCTURAL DESIGN 



maximum pitch in stiffeners is determined by the loading, if any, 

 but should never exceed a maximum of 4| ins. The load on an 

 intermediate stiffener, and the load plus the end shear trans- 

 mitted to an end stiffener, is divided by the bearing, or shearing, 

 value of the rivet on the plate to obtain the number of rivets. 

 These are equally spaced, but the maximum spacing is, as stated 

 above, 4 ins. 



When it is necessary to splice the web of a girder the splice 

 plates on each side of the web must be proportioned so the rivets 

 will not be unduly stressed. The moment causing vertical bending 



in the girder makes the 

 stress in the rivets 

 greater as the bottom 

 or top is approached. 

 Sometimes an addi- 

 tional " moment splice " 

 must be added on the 

 sides of the web close to 

 the flange angles. 



The lengths of flange 

 cover plates and the 

 spacing of rivets may 

 be done graphically. 

 In fact the graphical 

 method for obtaining 

 thelength of cover 

 plates is that commonly 



Fig. 73 



used by designers. Fig. 29 shows a moment diagram on a beam 

 carrying a uniform load and several distributed loads. Fig. 73 

 shows the combined curve for this condition, so that it will not 

 be necessary to measure up and down from the neutral axis and 

 add the lengths. 



The moment curve for a plate girder is similarly drawn. For 

 a uniform load only, the curve is a parabola, so it is necessary to 

 show but one-half the span. All horizontal measurements are 

 made to the scale of the drawing, and all vertical measurements 

 are made to the scale used for the bending moment. Make the 

 drawing no larger than is necessary to obtain accurate data. 



To set off the lengths of cover plates draw a vertical line through 

 the point of maximum bending moment, Fig. 74. Begin at the 



