— 119 — 
niches. The ratio of the latter to tlie total section of the chord bars 13 = 0,54 
Tlie ratio of ^ is ^ = 0.50， showing that if tlie elongations of the strut eyes be 
ma (l e according to tii e preceding theory, there will be a little play nofc taken up by 
尤 ho dead load, so it will bo necessary to make tlie elougfttions at say tho shoes and 
first panel points equal to that at the second panel points. 
Again in tlie 21 )0’ span on Plate XXXII the dead load stress at the middle is 
about 58 tons making the section for same 11.6 square inches and tlio ratio = 
H Tlie ratio of ^ i s — = 0.50, or greater than that last founcl, showing that in 
this case also tlie elongations of tlie pin lioles at tlie shoes and first panel points 
musfc he reduced from the theoretical amounts. 
Finally i u tlie 120， span on Plate XXII the dead load stress at tlie middle is 
=out 23.23 tons, and the ratio of sections -q= 0.414; while tlie ratio of 合 is 
口 = 0,55, This great difference is not of muclx importance for the ratio of ^ in tlio 
Glu ^ Panels is so small that the chord bars alone are about sufficient to take up 
tho stresses caused by an engine load or engine loads near one end of the bridge, 
consequently if the pins do lie loosely in the strut eyes when tlio bridge is empty, no 
urm will be clouo ； for vibration may be avoided by carelul cliord packing. 
Henco wo may conclude that the preceding theory of strut eye elongation may be 
adopted in all cases at all the panel points except one or two at each end of long 
s P^-us, at wliicli places they may be made equal to that at the next panel point 
towards tlie middlo of tlie span. 
“ Chord packing M is a term applied to the arrangement of the chord bars, chord 
strut, diagonals, posts, and beam hangers upon tlio bottom chord pins. It is a 
matter of great importance, but is very often neglected. The three principal consi- 
^eiations to be kept in mind while arranging the packing are, that tlie bending- 
^oments on the pius are to be made as small as possible, that the packing is to be 
as close as circumstances will permit, and that there be sufficient clearance to 
avoid all clianco of finding the space between tlie post channels too narrow wlieu 
the brid ge is being erected. . 
The wicltli of the packing is tlepeudenfc, not only upon the number and thickness 
0 tlie bars, but also upon the width of the top chord plate. The latter is often, in 
1 8 ^ lu, dependent; upon the chord packing. 
The best arrangement is to pack tlie main diagonals, counters, chord strut 
aud beam hangers inside of tlie posts, and the chord bars outside ; bringing the 
ei * ho'vevGi.， within the batter braces at the shoes, unless the end panel contain 
bars per truss, wlien two should go outside, and two inside. It is nofc abso- 
/ ely necessary that the chord bars pull in tlie exact line of tlie trusses ; an incli or 
of deilectioii in twenty feet being scarcely noticeable and making no appreciable 
1 eience in tlio length of the bar ; nevertheless it is bettor to mako tlie bars as 
neaily aa possiblo parallel to the planes of the trusses. The main diagonals should 
e P aceu next tlie post, then the beam hangers, and inside of all tlio counter or 
coimters an( i chord strut, if there be one, any vacant space thus left being adjusted 
1 The arrangement of tlie chord bars will be treated further on. 
