184 PRACTICAL STRUCTURAL DESIGN 



stresses should be investigated when high unit stresses are 

 used. 



The advantages of the type of joint shown in Fig. 109 are best 

 summed up in the words of Mr. Dewell: 1 "In this joint, the 

 strut has a full bearing on the butt block, and the butt block, 

 in turn, utilizes the total width of the chord for bearing. Also, 

 the detail takes advantage of the full bearing pressure in end com- 

 pression of the butt block on the chord, resulting in a minimum 

 depth of cut into the chord. Nearly all the cuts are normal, 

 and the others are simple. All the cuts can be easily and accu- 

 rately laid out and made by the carpenter. The length of the 

 butt block can be adjusted to fit all conditions of possible inter- 

 ference with other connections. Its minimum length is deter- 

 mined by longitudinal shear. The bolt through the end of the 

 butt block holds the block securely in its socket. Whether there 

 is any actual tension in the bolt depends upon the length of the 

 butt block. This can be determined at once by inspection. If 

 the line of the thrust of the strut falls within the base of the 

 block, there can be no tension in the joint. However, it is well 

 to provide at least a f-in. bolt to bind the joint together thor- 

 oughly." In another place, Mr. Dewell says: "The detail of 

 Fig. 109 is seldom used; nevertheless it is the most consistent 

 and logical in principle and the simplest of construction of the 

 three types shown." In the foregoing remarks the author 

 heartily concurs. In too many cases draftsmen, not entitled 

 to be termed designers, merely butt opposing diagonals against 

 one another with no provision for transmitting the component 

 of the diagonal stress to the chord. Designers must never forget 

 that all forces can be assumed to act along lines: these lines in- 

 tersect lines in other members and the force is then divided and 

 goes in two directions. The main force is termed the resultant 

 and the other forces the components. This will be discussed 

 fully in the chapter on Graphic Statics. 



Pin Connections 



A pin connection is sometimes an economical connection. It may 

 be used with either wooden or metal frames. The pieces connected 



1 Western Engineering, Oct. 1916, p. 386. 



