202 APPLIED MECHANICS 
members of a truss should either meet at a point or form a triangle. 
All members of the truss should either be simple ties or struts. Struts — 
should be as short as possible, and as many members as possible should 
be in tension. 
The feet of the principal rafters rest in shoes, which rest in turn upon 
wall plates, bolted to the walls or other abutments. 
185. Forms of Roof Trusses.—Figs. 278-283 represent six of the 
commoner forms of “ King-rod” and “‘ Queen-rod ” trusses. The member 
depending from the apex at the junction of the principal rafters is called 
the king-rod, while the other ver- 
tical suspension rods are called Peas <a 
queen-rods. : 
Fig. 278 shows the simplest , Fic. 278. Fic. 279. 
form of iron roof truss. The prin- 
cipal rafters are only supported at their ends, and a single king-rod with the 
tie rod complete the framing. This design may be used for spans up to 
15 feet. In Fig. 279 each principal rafter is divided into two equal 
panels by a secondary brace (a strut), and the span may be increased to 
about 25 feet. 
The design shown in Fig. 280 may be used for spans up to 30 feud 
By dividing each principal rafter into three equal panels, and adding 
Fie. 280. Fie. 281. 
two queen-rods in addition to the king-rod, as shown in Fig. 281, the 
span may be from 35 feet to 45 feet. 
The design shown in Fig. 282 is sometimes called an English truss, 
The principal rafters elite 
are each divided into 
four equal panels. This 
truss may be used for 
spans up to 60 feet. 
The saw-tooth or 
workshop truss is shown 
in Fig. 283. This form 
of truss is extensively used for the roofs of weaving sheds and the like, 
The slopes of the rafters are unequal, the covering on the lesser slope 
being slates or tiles, while that on the . 
greater slope is glass to light the in- 
terior. The truss shown may be used 
for spans of from 20 feet to 35 feet. 
King and queen-rod roof trusses, 
having vertical members, are very ” > 
suitable for hipped roofs. They Fr. 288. , 
have the disadvantage that the long braces are struts and the shot 
ones ties. This is sometimes obviated by sloping the diagonals. in the 
Fig. 282. 
