DESIGN OF STRUCTURES 209 
here, or by a special ridge member. Examples of ridge joints and 
‘methods of connecting the secondary braces to the rafters are shown in 
y. 292. 
Further detail illustrations, mainly relating to struts and shoes, are 
given in Fig. 293. Struts are usually angles or tees, or combinations of 
em A simple and efficient strut is formed of. two flat bars, or two 
bars of other suitable section, held apart by distance pieces suitably 
d Such a strut must be arranged to carry the total load upon it 
while acting as a whole, and must also be strong enough between the dis- 
tance pieces to resist local buckling. The attachment of struts to the rafters 
is usually by means of gussets, but they may also be attached directly. 
Angles, tees, etc., are sometimes joggled at the ends to suit the rafter. 
_ Shoes may be made of cast-iron, but built up shoes from rolled 
sections are common. They must hold the end of the rafter firmly, 
allow convenient attachment for the tie bar, and afford suitable bearing 
’ for the truss. The axes of the tie bar and rafter should meet at a point 
_ on the line of the vertical reaction from the wall or support. When the 
ItljIJ s@ 
Fia. 295. 
truss rests upon a wall a stone templet is provided for the shoe to rest 
upon ; Lewis or rag bolts let in with lead form a suitable holding. When 
the shoe is to slide, slotted holes are provided for the bolts. Sliding 
shoes often rest upon sole plates. 
__ Ties and their connections are shown in Fig. 294. Flat bars placed 
with their widths in the plane of the truss form good ties. Round bars 
may look neater, but they are more costly than flat bars as ties, especially 
for large sizes. Angle and tee bars work in well for ties of large section. 
With flats, angles, etc., the joints are usually made by means of gussets 
with rivets or bolts. In the case of round tie bars, forked ends or eyes 
may be forged on them to make pin joints. Another practice is to screw 
the ends of round tie bars, and the ends are sometimes staved up before 
Serewing in order to save weight. Adjustment may be obtained by 
making a cottered joint, or by cutting the rod and introducing a turn- 
buckle. With good workmanship such adjustment should be unnecessary. 
At the foot of the king-rod a tie between the trusses is often introduced ; 
this prevents lateral movement of the tie rods. 
; Fig, 295 shows cross sections and details of fixings for purlins. 
) 
