— 170 — 
reallv be the case if the pin holes be properly slotted. The reason for so doing is 
that, as a general rule, rivetted members should not be subjected to tension, but, if 
they be so subjected the number of rivets used for the connection 811011 Id be greater 
than that called for by theory. Then again, because of the cambre, there is a 
tendency to straighten out the strut-, tho bending moment of which must bo resisted 
by tlie rivets at the joints. As the assumed total tension on the strut is about twice 
as great as that to which it would be actually subjected, the theoretical number of 
rivets required has been doubled, which, all things considered, is not making too 
great an allowance for safety. 
We will put a joint at the second panel point) from eacli end of the span, and 
another at the middle. 
For the other panel points reinforcing plates will be required to compensate for 
the material lost at the pin hole. The greatest area lost is 0.3 x 4 = 1.2 square 
inches, corresponding to six tons of stress, tho moment for which is 6x0.4 =2.4 inch 
tons. This divided by 0.494 gives 11 as the total number of rivets on both sides of 
the pin hole, oi* six on each side. It will be bettor to make this number eight on 
a side, for fear that the reinforcing plato be called upon to bear more than its cal- 
culated stress. A thiclmesa of fand a maximum depth of S n will more than com- 
pensate for the material lost in tlie web, and the lever arm being thus slightly reduced 
will lessen the bending moment upon tlie rivets. A drawing to scale will show that 
the length of each plate should be about 3’. Those at tlio ends of the span may be 
made nearly a foot shorter. 
Next let us proportion the reinforcing or connecting plate at tlie shoe. 
The greatest live and dead. load stress at the channel bearing is say i (54.432 
一 5 x 2.8) = about 20 tons. Referring to Table XV. we find the necessary bear- 
ing for this stress upon a 8 ^ pin to be l x y f . Table XVI. gives tlie tlxiclsness of web 
for a 12" — 86.82 pound channel as 0.G2", wliicb, subtracted from 1 A〃， leaves 0.45 r 
say as tlie thickness of plato required. If L be the length of the greatest section 
of this plate by any plane perpendicular to the batter brace, then i x L should not 
be less than the area of one batter brace chanuel. Supposing equality we have 
^ Zv = 10.9 and L = 21.8". 
This condition will receive attention presently ; meanwhile we will assume the 
thickness to be i", and calculate the number of rivets required by multiplying the 
stress on one channel (10.9 x 2.889 = 81.5 tons) by the lever arm | (0.62 + 0.5) 
= 0.56, anti dividing the product (17.64 inch tons) by 0.49 4, the resisting bending 
moment of a l f, rivet, making the number 85. 
For this connection we can use five rows of rivets spaced two inches apart, and ft 
pitch of about three and a half inches so aa to bring the rivets into horizontal lines 
aa in the accompanying diagram, wliicli is 11m« drawn. Lay out a horizontal liw 0 
A 13, and from any point A uraw the lines AG and A H, making angles with A B to 
correspoml to tlie arc whose tangent is ff. Draw C D anil E F parallel to A B an^ 
at distances therefrom equal to ^ (20 〃 -- 2 x 2.85") = about 7", cutting A G an^ 
A II in C and E. Draw N O and P Q parallel respectively to A G and A H, an^ 
at distances 6 ,r therefrom. Draw also the parallels J K and L M 6 A, from N O and 
