—— 137 — 
^heve .jj iy the area of the section of the post, and k the depth of one of its cliannela. 
Next resolve one-half of the diagonal stress vertically and horizontally into 
1 a ud Z)’ respectively. Let l represent the distance between the centre of the diag- 
° ua ^ au d that of the extension plate, and l f the distance between the former and that 
d Ü 10 cUord- bearing ; then 
1* FI, 
h = vn\ 
aud 
M— 
K üie bridge be a small one, it will he necessary to calculate only the size ot the 
at the top of vertical post from tlie end of the bridge, aud to make all 
“ e ^texiuediafce top chord pins of the same size. But, if the bridge be a large 
0 加 ， it will be bettei* to calculate the diameter of the pin on the post midway between 
tlle vertical post ami the uiitMlc of fclie span, and to make all the pins between 
tllese Peaces of tliis diameter, and all the others of the same diameter as that at tlie 
e Mof the first vertical post. After the diameters of the top chord pins are cletev- 
miued， the posfc au l chord bearings should be tested by applying Table XV, al- 
1 10u gh in most cases they will be found ample. 
In double-intersection bridges, \vhcre the diagouals are lnilved, and coupled on 
losing tlirough the middle of the posts, the size of any one of these pins may 
be foui1 ^ from the moment 
^töie S is the stress on the diagonals as given on the diagram of stresses, and ir the 
width of o Ue 0 f tl ie main diagonals. 
In all pin proportioning it must be kept in mind that the diameter of the pm is 
never to be less than eight- tenths of tlie depth of the deepest bar coupled thereon. 
Tlie moment on any pin belonging wholly to a lateral system or sway bracing 
Ca u always be found by tho formula 
ü/= PL 
|vheie i J iy ^] ie reaction at one beariug and l tlie distance iroin the centre of this 
Jeaiiug to tlie centre line of the force wbicli produces l\ It must not be forgotten 
la on b" one set of diagonals of a lateral system can be in tension at once, and that 
le 也 ess on any diagonal (where single diagonals are used) should be divided 
ly between the bearings, making P equal to half the greatest working stress on 
le clia o° nal including initial tension. 
The value of l and consequently that of M can be reduced by making the eye 
文 square iron and welding it to the rod. 
The author wishes to call attention to the superiority (in bis opinion) of the 
lln ^ e Method given for proportioning lower chord pins by formula over the apparently 
111016 ac(iui ，ate one previously explained. 
the former method, when the proper proportion of width to depth of bar» is 
