218 APPLIED MECHANICS 
Various means are adopted to place the rivets in a flange joint in 
double shear. The rivets which do not pass through the flange angles 
_ may be placed in double shear by the addition of covers underneath the 
flange plates, as shown in Fig. 316. The addition of round back covers 
to the angles, as shown in Fig. 317, will place the remainder of the 
rivets in double shear, but these angle covers cannot act as just stated 
Fria. 316. Fig. 317. Fig. 318. Fia. 319. 
and also act as covers to a joint in the flange angles at the same time. 
* The underneath cover may extend right -across the flange, as shown in 
Fig. 318, which is a section of the flange in the neighbourhood of the 
joint. This, however, prevents the flange angles being placed directly 
on the flange plates, and where the covers do not occur, packing pieces 
have to be introduced, as shown in Fig. 319. These packing pieces 
cannot, however, be counted as forming part of the flange section, at any 
rate in the neighbourhood of a joint. 
The thickness of each flange plate should not be less than 2 inch or 
greater than # inch. Four 3 inch plates, or three } inch plates, make a 
much better flange than two ? inch plates, supposing the required flange 
thickness to be 14 inches. 
197. Web Plates.—The web in small plate girders consists of a 
single plate suitably stiffened to resist the shearing forces. Except for 
. very small and unim- © 2 i eee 
portant girders, it is ITT YT oo 
not desirable to make & * ° °1° ° 
the web plate less than e elee 
2 inch thick. On the 1 
other hand, the thick- ve. os eS 
ness of a single web (3 e-% 
plate should in general ' pS 
not exceed # inch. pistes: meer 
When more than e e1ee 
one plate is required 
to form the web, the as Aa A nee 
different plates are “7-7 —W—W—vW—ao— 
united by butt porns §$—_—=_—_—-— 
with double cover 
straps, as in Fig. 320, Fig. 320. Fig. 321. 
which shows a vertical joint in a web. Sometimes stiffeners are utilised 
to do duty as covers, as shown in Fig. 321. This figure also shows how a 
change in the thickness of the web plate may be effected. Such changes, 
made with the idea of proportioning the thickness of the web to the shear 
stresses, are only advisable in large and important girders, or when 
