JOINTS AND CONNECTIONS 



201 



The shear on each rivet due to direct stress is 



Each rivet has also 

 some stress due to 

 bending moment. 



The necessary resist- 

 ing moment is found 

 as follows : 



13,720 



4573 Ibs. 



M 



in which 



M = resisting moment 



A = stress in a rivet 

 due to bending. 

 x, y and z represent, Flg- 118 



respectively, the moment arm for the rivets bearing these letters. 



Transposing, 



M 



56,290 



= 8650 Ibs. 



x 1 + y 2 + z 2 6.513 



The stress in each rivet due to bending is equal to this figure, 



multiplied by the distance of the rivet from the center of gravity. 



Stress on x = 8650 x 1.46 = 12,640 Ibs. 



Stress on y - 8650 x 1.46 = 12,640 Ibs. 



Stress on 2 = 8650 x 1.50 = 12,980 Ibs. 



Adding the direct shearing stress to these figures, by the paral- 

 lelogram of forces drawn in Fig. 118 the resultant stress on rivets 

 x and y is 15,600 Ibs., as shown. 



The web thickness of a 10-in., 25-lb. I-beam is 0.31 in. The 

 bearing area of a f-in. rivet is, therefore, 0.31 x 0.75 = 0.2325 

 sq. in. 



15,600 Ibs. divided by 0.2325 = 62,100 Ibs. per sq. in. bearing 

 stress on web of beam. This is more than three times the amount 

 shown as permissible in the rivet table, where the allowable stress 

 in bearing is 20,000 Ibs. per sq. in. The connection here shown 

 is, therefore, not good for a reaction of 13,720 Ibs. 



In Fig. 119 at (a) is shown an angle connected by both legs 

 to the gusset plate. Only one hole is deducted, for the holes are 

 staggered to preserve the net section. This staggering is done 

 also, when not necessary to preserve the net section, in order to 

 permit of driving the rivets in two legs with plenty of "clearance." 



