DESIGN OF STRUCTURES 217 
196. Booms or Flanges.—The booms, or flanges, of built up girders 
are almost invariably made up of flats* or plates. These are united to 
wee Me = He == = mmm ow ow le ow wm « oh one woes 
O\E 9 G'9 02 939 89 G:190 9 09/92 99d 
Fia. 313. 
the web plates by angles, which of course act with the plates in resisting 
the bending moments. 
The boom plates are not all of the same length, but are curtailed as 
the bending moment falls off. The usual graphical method for determin- 
ing the length of the flange plates is shown in Fig. 331, p. 227. Care 
should be taken that 
theangles and platesare @-@-a.@—0—044_44_2_2a— 
of convenient lengths. @ooooood0o0e000e090o 
When there are many 
plates in a boom, the Fig. 314. 
joints in them should be 
grouped, where possible, under one cover, as shown in Fig. 313. It is, 
however, sometimes convenient to make one flange plate form the cover 
for the joint of another, as shown in Fig. 314. 
Joints in the flange angles are made with rownd back covers, and are 
arranged as shown in Fig. 315. 
In the type of grouped joint shown in Fig. 313, a single cover is used 
and is placed on the outside, hence the rivets in the joint, although they 
IO 90(9.9,.0:0.9,0:0.0,0) 0 
Se a OO Oe! le re CO 
O92 ,,9,,9,,9,.9,.9,.9, PO 9 
@ OXo%0"0"0"0" OOO 0] 
Fie, 315. 
pass through several plates, are only in single shear. An underneath 
flange plate or angle must not be regarded as forming a cover to the joint 
in a plate above it, for it has its own load to carry, and cannot act as a 
flange plate and also as a cover at the same time. 
* Flats are narrow plates, rolled to definite widths, usually not exceeding 
12 inches, 
