— 158 — 
counters are preferable, although they necessitate rather large pins for the ' tipper 
chord. Looking clown the column for square sections headed“ Intensity of Work- 
ing Stress = 4 tons ” in tlio table we come to a stress of 0.81, the next groater yalue 
to 9.746, and following oufc the horizontal line containing this stress wg see that a 
square bar will be required. 
Although theory does not call for one, 've will put a single V round counter in 
the third panel, to aid in adjusting the bridge and to assist in taking up shock. 
By referring to Table VII. we see that two l\ n X 2^ bars will be required for tlie 
hip verticals. 
Next let us proportion tho bottom chord strut. The greatest stress was found 
to be 13.827 tons. It will be necessary to use six inch chamiels, for the webs of 
smaller ones would bo too much cub up by the pin boles. 
The ends of each panel length of strut may be considered fixed, and tlie number 
of diameters is - 12 = 42. Consulting Table VIII. we find for these data a 
working intensity of 2.422 tons, which divided into 18.827 gives 5.7 square inches, 
correspondmg to t、vo (i" — channels. As this member acts as a strut only for 
wind stresses, it might appear better to employ Table IX., but because it acts also 
and generally as a tension member, it is better to employ a small intensity of work- 
ing compressive stress ； besides, as said before, any extra material put in the Avebs 
of the channels is not wasted, for it will assist in resisting tension. 
Referring to Table XVI. we see that the thickness of web of a 6" — 9,5* Union 
Iron Mills’ channel is 0.3 inch. If we usg g" rivets for attaching tlie connecting 
plates at the joints, the area lost from each channel will be 2 x 0.3 x = 0.41 口", 
and from the two channels 0,82 口" leaving 2 x 0.3 X G — 0.82 = 2.78 say 2.8 □” 
as the effective area of the webs, which area must be subtracted from S. R. in pro- 
portioning the bottom chord bars. 
By referring to Carnegie’s sections of flat bars in Chapter II. we can propor- 
tion the main diagonals ami chord bars as mauked on the diaguam. The pro- 
portion of width to depth of chord bars should be noticed : ife is made as nearly in 
accordance with the theory of Chapter XIII. as cii.cumsfcauces will premit. For 
appearance tlio widths of the main diagonals decrease towards the middle of the span. 
Next let us proportion the top cliord. From Plates XXVI. and XXVII. we 
find that 12" channels must be employed, which makes the ratio of length to least 
diameter equal to 21. 
Referring to Table VIII. we find the intensity of working stress for two fixed 
onds to be 3.543 tons, which divided into oaclx of the stresses gives tlie sections re- 
quired as marked on the diagram. 
The width of top plato was assumed as ?.0 パ (we will check it presently to see if 
it be sufficient), and its thickness 811011 U be 蚤" (vide Chapter VI.), making the area 
3 ノ X 20" = 7.5 öubfcractiug this from each of the sections requived aihI 
multiplying each remamaer by ten sixths will give the weight of one channel bar for 
each panel as marked on the diagram. 
Next let us proportion the batter braces, for which the ratio of length to least 
