— 187 — 
DB. 
Let I = panel length in bottom chord = GD 
c = i increase of panel length in top cliord. 
ゴ = depth of truss between centres of cliord = AB. 
な = angle between radial lino at panel pt. and 丄 to chord. 
Tlien Q：= sin —J -i- (Eq. 1) DF ： c ：: l : d r.*T)E = 
Bq -5 ； 2 — r» /»o Id 2 一 c 2 
el 
IT 
d- 
.( Eq .2) 
ö can be taken equal to GD + DB = 6 1GD without perceptibly affecting the 
final 
result. 
In triangle ABG t AB anti BG are known ; also angle ABG =. 90° -f 2¢. 
仙 + ^ [180°— (90° + «)]: tan i [BAG — BGA] ; 
Again : 
BA(J — «BGL4 = 2 tail — 1 
ab — bg 
A.J j JJ(jr 
tan ( 45° 
also 
( BAG — BGA) + ( BAG+ BGA ) = 2 BAG = 
( BAG 一 BGA ) + ( 90® — 2¢) , which gives BA(r\ 
BGA 
finally, 
‘4G = 
180。— （7? ⑽ + (jo 。 十 ‘ 2a ) =f)(r — （ ル⑽ + 2 a )： 
Iß cos BAG + BG cos BGA = length of diagonal required. 
^ch j le hg 山 of the diagonal as manuftictured should be one sixty- fourth of an 
a v S ? that calculated, so as to allow for tho play of the pins in the eyes. 
8l uall 1,0 デ ア allowance for play is permissible, it is better to take the next 
not co S if, after making the redaction just indicated, the length should 
botto 班 ' ° Ut 0U an exac t sixfcy-fjurth. Because of the play in the pin holes ot the 
心 c ミ ' i0rt l bai.8, the panel length of tho manufactureil top chord should exceed 
^ CU a t、 e d ^ en gtli by about a thirty- second of au inch. 
別 thouf^i 仙 013 も 山 8 elevation of the chords, posts, diagonals, and batter brace, 
their d. S ° W ^ details. Alongside of each tension member show the heads with 
of 山 ^ 111611 ^ 0118 , aiK 】 on ル 6 81101 *toneiI distance mark the size of the bars, the nurnbei 
こ ’ aud tlie length from centre, to centre, as shown on Piate X. 
c °nve ' 10 l ^^^ iau( ^ ßnd of the drawing, or on a separate alieet, whichever be more 
浓 ithout^t’ d law out tlie lxeads full size, placing one on tho other, if this can be done 
centre C ° U . Us ^ on, Sometimes as many as six heads can be represented about ono 
F’of; 0 ' Med that both pins and heads diminish together, 
describ^ J ammere( ^ heads the method of construction is very simple. It consists in 
6( 1 如 1 to G’. 邮 わ 奶 g • エ 0 f tlie accompanying diagrams, a circle of radius GA, 
of the piu hole, and a portion of another circle with a radius Cß ， equal 
