202 



PRACTICAL STRUCTURAL DESIGN 



When an angle is connected by both legs the total area of the 

 angle, less the area of the holes, is taken. When an angle is 

 connected through one leg, as at (6), the load will be eccentric. 

 The problem is then complicated, but an easy practical solution 

 is to use only the area of one leg. 



Problem. An angle in tension has to carry a load of 50,000 Ibs., 

 using f-in. rivets. 



50,000 



Area of member = -r = 



16,000 



= 3.12 sq. ins. 



Fig. 119 



If connected by 

 the two legs try a 

 5" x 5" X f", the 

 area of which is 3.61 

 sq. ins. (Carnegie, 

 p. 146.) The area of 

 the hole is I" x f" = 

 H* = 0.328 sq. in. 

 The net area is 3.61 

 - 0.328 = 3.282 sq. 



ins. Notice that the diameter of the hole is \" greater than the 

 diameter of the rivet, giving T V clearance. This rule is general 

 for all rivets. 



If connected by one leg it is assumed that this leg will carry 

 all the stress. Assume a thickness of ", and as the area is 3.12 

 sq. ins. divide and add, to the width thus obtained, the diameter 

 of the hole. Then 3.12 + 0.5 = 6.24" + 0.875" = 7.115". This is 

 plainly not suitable, for it does not fit any standard angle. Try 

 a thickness of f" and we get 3.12 -=- 0.625 = 5" + 0.875 = 5.875". 

 This is nearly six inches, so we will use a 6" X 3^" x f " angle. 



The practice of using j-in. and fV-in. gusset plates in roof trusses 

 is very common, yet considerations of economy, as well as effici- 

 ency, would seem to indicate the use of thick plates. The plates 

 should be of such thickness that the bearing value of a rivet in 

 the plate is about equal to the value of the rivet in double shear. 

 This would reduce the number of rivets in a joint considerably 

 and reduce the size of the plate correspondingly. The slight in- 

 crease in the weight of the plates is apt to be more than offset 

 by the reduction in the number of rivets. The use of thicker 

 places and fewer rivets also measurably reduce the secondary 

 bending stresses in the members due to fixity of their ends. The 



