238 APPLIED MECHANICS 
24 inches x 23 inches are also used. Various forms of secondary bracing 
are shown in the illustrations of this section. 
; The stresses in the web members are found from the stress diagrams 
(see Chapter XII.), and their cross sections determined by the rules for ties 
and struts, 
Where the connections between a strut and the booms are’ stiff 
riveted joints, and the boom sections are also stiff and capable of with- 
Fie. 365. 
standing considerable bending and distorting moments, the strut may be 
considered as fixed at its ends, or nearly so. It is safer, however, in 
order to allow for any imperfection in the manner of fixing to take the 
effective length of the strut as, say, 1} times its real length. 
212. Connection of Web Bracing to Booms.—In English practice 
riveted joints are almost invariably used for connecting the web braces to 
the booms. Examples are shown in preceding illustrations. In America, 
pin joints, such as shown in Fig. 375, are common. ; 
If the number of rivets required in the ends of the web members is 
not too large, these members may be attached directly to the stringer 
plates, as shown in Figs. 356, 360, and 362. Often this is not possible, 
and gussets are introduced, as shown in Figs. 363, 364, and 365. In 
Figs. 364 and 365 the rivets in the ties- are placed in double shear by 
the use of cover plates. 
The following conditions should be observed when designing joint 
connections :— 
(a) Sufficient rivet section should be provided in each member to 
take the load on it. If gussets are used, sufficient rivets must pass 
