214 



PRACTICAL STRUCTURAL DESIGN 



were not drawn in this way there would be a vertical line with a 

 gap in it and the letter m and the letter I would be repeated. 

 Since there is but one member with these letters there can be 

 but one line in the reciprocal diagram having these letters at 

 the ends. 



In Fig. 129 is used for the first time the most orderly arrange- 

 ment of letters to designate truss members. Beginning at the 

 left the letters run consecutively along the outside of the truss to 

 the extreme right and continue in the same consecutive manner 

 back to the left. When the loads are laid off on the vertical load 

 line the letters run in regular order. This is a convenient way 



n 



c R, 



d 



Q- 



e 

 f 



Fig. 129. Truss with Cambered Tie Rod. 



when the truss is unsymmetrically loaded and is, therefore, con- 

 venient when it is symmetrically loaded and but one-half of the 

 reciprocal diagram is shown. Capital letters are used on the truss 

 diagram and the corresponding small letters shown on the recip- 

 rocal diagram. The joints are numbered, in order that the joint 

 referred to may be described readily with the fewest words. This 

 system for numbering joints is used generally for trusses having 

 non-parallel chords. Trusses with parallel chords have the joint 

 numbered with the letter U prefixed to the number on the 

 upper chord and with the letter L prefixed to the number on 

 the lower chord. The student is advised to use the method of 

 lettering and numbering shown in Fig. 129. 



In Fig. 130 is shown a simple Fink truss with cambered tie rod. 

 The Fink truss is said to have been invented by Albert Fink and is 

 an early form of metal truss. In Europe it is known as the Belgian 

 truss and is commonly supposed there to have been the invention 

 of a Belgian engineer. In some English text books it is called a 



