— 53 — 
plane of the truss, (see Plate IX, Fig. 11). In short spans this strut may be omitt- 
ed by trussing the inner chord bars, as shown on Plate IX, Fig. 10. 
Side braces may be made of angle or tee iron, but preferably of channel iron as 
Bhown on PL IX, Figs. 10 and 17. 
Floor beams and most track stringers are built of plates and angles as shown on 
Plates III and IY, but, when the panel leugtli is short, I beams can be advantage- 
ously employed for tlie track stringers. 
Main diagonals arc always eye bars, and counters are of square or round section 
witli loop eyes at the ends. 
Hip verticals may be of round, square or flat iron : it is customary to make them 
narrower and thicker than main diagonals or chord bars, perhaps because iron in 
sucli a shape is stronger than wlien rolled into tliin bars, and much strength is 
needed in those membevs to resist sliocl“ Counters are alwtiys adjustable, i. e. are 
provided ■with an arrangement by wliicli they may be sliortened or lcDgtliened, but 
main diagonals, "chord bars and liip verticals are of invariablo lengtli. 
Lateral and vibration rods are nearly always round, but there is no particular 
objection to making them of square iron : tliey are always adjustable. 
It is not considered good practice to vary tlio tliicknoss of tlio top chord plate 
or to increase tlie number of thicknesses towards the middle of the span ; for tlio 
proper place for the larger part of tho material iu a top chord is in tlio channels aiul 
not iiitlic plate. Similarly in any channel the best place for tlie larger part of the 
material is in tlie flanges and not in tlie web, nevertheless both thick aud tliin clian- 
uel webs are necessary for tlio same structure. 
Channels in struts generally have tlieir flanges turned outward, although ， 
theoretically, as far as tlie strength of tlie strut is concerned, it is better to turn 
them the other way, for tlio moment of inertia of tlie section is greater ； nevertheless 
the difficulty of rivetting in a confined space more than equalizes the advantage thus 
gained . 131 it there are certain cases, for instance iu bottom chord struts, in whicli 
it is better to turn the flanges inward notwithstanding tlio difficulty in rivetting. 
It is not well to reduce to any extent the widths of tlio flanges at the ends of 
strut channels, as thereby tlie strut is weakened ; but a slight trimming may bo 
effected, if tlie channels bo well re-inforced. 
Main diagonals, as will be demonstrated in Chapter XIII, should liave tlie pro- 
portion of width to depth about one to four, and tlie chord bars that of from one to 
lour to one to seven, according to tlio number of them in the pniiel. 
Top chords excop t for very short spans are made up of lengths ecpial to a panel 
length， so there is a joint in the channels and plate near every panel point . 丄 his 
joint is placed tlireo or four inclies from tlio panel point and towards the noarei end 
of the span, in order that tlio piu bole may not be bored througli two abutting ends, 
as is unavoidablo at the hip joint. The abutting ends of each pair of channels ai'e 
connected by a splice plate or connecting plate on each side of tlio web, making foui 
plates to an ordinary joint besides tlie coyer plate wliicli connects tlie abutting ends 
of tli g cliorcl plates. This detail is represented on PI. IX, Fig. 7. 
The connection at tlie liip is made by means of two plates on the outside of tlie 
