JOINTS AND CONNECTIONS 



187 



between the second and third bars is equal to the moment just 

 found plus the difference between the loads on the first and 

 second bars times the moment arm between the second and third. 

 The moment between the third and fourth bars is equal to the 

 last moment plus the difference between the load on the first bar, 

 less the sum of the loads on the second and third, times the mo- 

 ment arm between the third and fourth bars. In determining 

 the vertical moment multiply the vertical load by the distance 

 between centers of the vertical member and the most distant 

 inclined member. If there are a number of inclined members 

 then proceed as in computing the horizontal moments, using 

 the vertical loads. 



Referring to Fig. 110 the loads on the members are designated 

 as PI, P, Pj and P 4 . The moment arms are designated as A, 

 B, C, and D, being in inches. The resulting moments are desig- 

 nated by M a , Mb, M e , and Md. 



At Pj the moment = Af = PI X A. 



At P, the moment = M 6 - M + (Pi - Pa) X B. 



At P 4 the moment = M e = M 6 + (Pi - P 2 + P) X C. 



The members P 4 are inclined and the center piece is vertical. 

 The vertical moment is equal to the vertical load multiplied by 

 the arm D. The vertical member is made of two channels and the 

 other members are eye bars. 



Fig. Ill is from the 1913 edition of the Carnegie Pocket Com- 

 panion. A pin has to carry a load of 64,000 Ibs. : 

 required the size at 24,000 Ibs. fiber stress, assuming 

 the distance between points of support to be 5 ins. 



Bending moment = 64,000 x 5 + 4 - 80,000 in. 

 Ibs. This it is seen considers the center load as 

 concentrated and allows nothing for the distribu- 

 tion of the load over a part of the span. The size 

 of the pin may be obtained from the table on page 

 219 in that book. Looking in the column headed 

 by 24,000 find the nearest (larger) resisting moment, 

 which is 80,900 in. Ibs. In the first column at the 

 left is the diameter, 3J in. 



The size and diameter of the pin may also be found from the 

 expression, M - fAd + 8. 



