158 



PRACTICAL STRUCTURAL DESIGN 



stress on the edge of the table and the tensile stress in the uncut 

 portion of the fish-plate which is equal to one-half the thickness of 

 the fish-plate, in this case 2 ins. These two equal and opposite 

 forces constitute a couple acting on the fish-plate equal to one-half 

 the stress in the chord times one-half the thickness of the fish- 

 plate, or, 22,500 Ibs. X 2 ins. = 45,000 in. Ibs. This moment 

 must be resisted by tension in the bolts acting about the bearing 

 face of the tables. The bolts should be placed on the vertical 

 line through the center of the tables. Their lever arm is thus 

 equal to one-half the table length, in this case 11.5 in. The ten- 



45 000 



sion on the bolts = - -=- = 3920 Ibs. Two bolts will be used 

 11.5 



having an area of 0.3920 sq. in., for the stress on wrought iron bolts 

 should not exceed 10,000 Ibs. per sq. in. The nearest size is found 

 to be f in. bolts, which have an area at the root of the threads 

 = 0.202 sq. in. and the combined area of two f-in. bolts = 0.404 

 sq. in. Two f-in. bolts therefore will be used in the middle of 

 each table and four more will be used as shown to bind the joint 

 together. 



In Fig. 94 is shown a steel-tabled fish-plate joint. This is a 

 joint that requires especially good and careful inspection. It is a 

 detail for members carrying heavy stresses. It costs considerable 

 for materials and on account of the number of tables required 

 the labor cost is high, for there must be very careful cutting to 



insure even and 

 snug bearing for all 

 the tables. 



Bearing area re- 

 quired for tables = 



45,000 __ 

 ionn = 37.5 sq. ins. 



2, %x8" Plates S'Oi" 



8, l%x.8"Tables,bearing edges mi/fed. All rirefs % 



12, %* Bolts. 



5ide Elevation. 



Total combined 

 depth of tables = 

 37.5 



Will use tables 



Mg - 94 (make it 2| in.). 



r 3 s- in. = 8 in., requiring 8 tables in all. 



Each table transmits 



= 11,250 Ibs. and requires three 



f-in. rivets, as determined by bearing on a T V m - pl ate ( see P a S e 



