JOINTS AND CONNECTIONS 159 



190). The tables are solid pieces of steel bar l-j\ ins. thick by. 3 ins. 

 wide riveted to the i j-in. plate used as a fish-plate. The thickness 

 of the fish-plate is determined as follows: 



Net section of one plate required = ^- ~ = 1.41 sq. ins. 



Z X 10,UUU 



Net section of ^ by 8-in. steel plate (deducting the three rivet 

 holes for the table rivets) = T 5 , x (8 - (3 x J)) - 1.68 sq. ins. 



Size of bolts required to resist moment on tables: Moment 



7003 



= 11,250 Ibs. x fi in. = 7383 in. Ibs. Tension in bolts - -^ 



o.o 



= 2110 Ibs. Use two f-in. bolts. 



8 x 120 

 Space between tables = t1 __,, + 1$ = 13J in. 



Sometimes the lower chord cannot be made of a single piece 

 spliced by means of a fish-plate or shear pin splices, but a number 

 of 2-in. or 3-in. planks must be used. The methods adopted for 

 splicing such chords are illustrated in Fig. 95. 



It may be assumed at the start that there should be an odd 

 number of planks, for the center plank has so much section cut 

 away for holes through which the verticals will pass, that it cannot 

 be counted on as furnishing any tensile strength. Usually the 

 middle rod is smaller than the others and about half the section 

 of the center plank is available at this point for tensile strength, 

 which is an additional factor of safety. The center planks are 

 regarded merely as blocks in which a bearing is obtained for bolts. 



The lower chord under consideration is so light that only three 

 planks will be used. The center plank will be 2 ins. and the outer 

 planks will each be 3 ins. thick. It is well to have the planks 

 rough sawed and not finished, as the rough surfaces increase 

 friction and also leave a small space for ventilation between the 

 planks. The length of the truss is 60 ft. center to center of bear- 

 ings, and, in the absence of data as to the end joints, we will 

 assume two feet added, making the total length 62 ft. The outer 

 planks must lap past each other for some considerable distance 

 to allow space for the bolts which will be used to tie them to- 

 gether. Assuming that planks may be purchased 8 ins. x 38 ft., 

 each side will have one plank 38 ft. long and one plank 62-38-24 

 ft. long. These lengths will be alternated so that at one end on 

 one side there will be a 38-ft. plank and on the opposite side of 

 the chord there will be a 24-ft. plank. This gives a lap of 14 ft. 



