一 121 — 
ar e to be proportioned by using Table IX for one fixed and one liingod end, and 
adding, if necessary, to the section thus found enough area to resist bending as 
determined in Chapter IX. 
Those struts do not really liave one enil fixed and the oilier liingecl, but the 
strength of a strut connected by abutting jaws is intermediate between that of a 
strut of tlio same size with both ends fixed and that of another strut of the same size 
witli both ends liingocl. This is because tlie inaccuracies of shop work may 
cause a slight deviation from axial bearing. 
It is not positively necessary to use a lateral strut between pedestals at tlie 
n xea end of all spans, but it is much better to do so, not only to distribute tlio 
horizontal reactions, but to keep the chords in line ; for there is necessarily a little 
play in the anchor bolt holes. 
There is generally no objection to making theso struts lighter than those at tlio 
れ ee en< l of tli e span, bufc ifc will often be found that considerations of detail will 
^Gcessitate tlio use of a strut nearly ns large as that at tlie free end . For instance, 
び there be a vertical pin 3 ま " in diameter passing through tlio jaw, it would entirely 
Cu t Away the flauges of an エ -beam， and would leave but little iron in two 4_" clian* 
ne ls so two 5 ff channels would be required. ， 
Again, the component of the stress in the end lower lateral rod in a direction 
pQ^pendicular to the strut will produce a bending on tlie connection, and an inequality 
of she«ai. upon the rivets which connect the jaw plate to the strut. To resist this these 
ぞ 1 vets should be spread apart as much as possible, and the nut which connects the 
to the chord pin should be screwed up very tightly and perhaps locked. It is 
0 vioua that this objectionable tendency to bending is less the uearer the vertical 
P l u is to tlie end of the strut. 
Tlie total working stresses (iwt inte antics) for I beams used as intermediate 
^ rills 111 single track bridges are given in Table X. Both end« may be considered 
xed， When the X-boam strut is supposed to bend in a vertical plane, its length 
should be taken equal to the distance between the points of attachment of the 
jackets ； but, when it is assumed to bend in a horizontal plane, its length must be 
a ieu equal to the distance between opposite posts of the trusses. 
Brackets slioakl extern! inward and downward, fi-om about four feet in narrow 
rid ges, to about six feet in wido oues. The sway bracing given in Table XIII 
^ as Proportioned for brackets of these dimensions. Brackets beneath intermediate 
8 ruts not only serve to stiffen tbo struts, but add to the appearance of the bridge. 
To proportion the bottom chord strut, find tlio greatest stress in any panel, as- 
sume the depth of the channel, which should be made so great that tbo bottom chord 
P x ns will not take too much material out of the webs, aud divide this stress by the 
be nSity 气 0 untl in Table VIII for both ends fixed. If the sectional area thus found 
e small, it can be increased without causing much waste, for any area added to the 
e s of the channels is merely taken off tliat of tlie chord bars. 
If the stiffening be accomplished by trussing tlio inner chord bars, it must not 
ö ol gotten that the intensity of working tensile stress is to be reduced to four tons 
ぞ — 一 that the intensity of working icuanc 叫 ！^。 ^ • — — — 
^ KJ bars so tiussed. Struts of trussed bars may be assumed to liave an intensity 
Working compressive stress equal to one ton for short panels, and half a toil for 
onno x 
a g ones. 
