220 APPLIED MECHANICS 
in compression along one diagonal, and in tension along the other. Since the 
thin plate is much less able to withstand the crumpling tendency of the 
compression than the direct tension, it is usual to consider the web as if 
composed of a number of parallel strips inclined at 45°, terminated either 
by the stiffeners or by the flange angles, and acting as struts. This con- 
sideration establishes a relation between the thickness of the web and its 
unsupported length. The shear force at any one section is assumed to be 
uniformly distributed over the depth of the web, which is very nearly 
correct (see Fig. 203, p. (150). This determines the shearing stress 
and the diagonal compressive stress, which is equal to it, and hence the 
load upon the strut. The foregoing reasoning leads to the construction 
of formule such as are given below. It will be observed that these 
formule are of the form of the Rankine-Gordon formula for struts. 
S=safe shearing force in tons per inch of depth at any section, 
found by dividing the total shearing force, in tons, at the 
section, by the over-all depth of the web plate there in 
inches. 
t= thickness of web plate in inches 
d= horizontal distance between centre lines of stiffeners, or vertical 
distance between centre lines of rivets in the boom angles, in 
inches, whichever is least. 
8¢ 
ot Mla Ere Se 
gent ty 2 
4000 | 
Another rule, due to Mr. Theodore Cooper, reduces to the following, 
5°36¢ 
In any case, S must not exceed 4¢. 
Preferably proceed graphically, as shown in Fig. 330, p. 226. Draw 
the shear per inch of depth diagram found as above. Plot on this lines 
parallel to the datum line representing the possible shear per inch of — 
depth of 3 inch, ;% inch, } inch, etc., plates, corresponding to the pro- 
posed spacing of the stiffeners, as found by one of the formule given 
above. An examination of such a diagram will show, either the limits 
between which a given thickness of web plate may be used with a given 
spacing of the stiffeners, or the limits between which a given spacing of 
the stiffeners may be used for a given thickness of web plate. This 
matter is further considered in connection with the worked exampig, 
Art. 204, p. 223. 
199. Riveting of Plate Girders.—For ordinary everyday work 
punched holes, 4; inch greater in diameter than the rivets, are usually 
specified. In first-class work the holes are punched 3}, inch to 4 inch 
smaller than the rivets, and reamered to size after the work is bolted 
together. The bolts are then removed, and the burrs formed by the 
reamer taken off, after which the work is riveted up. 
The riveting in the joints of the plates in the booms must be designed 
to carry the tension or compression which exists in the plates they unite. 
The riveting through the angles connecting the boom plates to the web 
