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PRACTICAL STRUCTURAL DESIGN 



confusion when an attempt is made to trace out the loads from 

 the middle panel, or point of zero shear. 



Some trusses have nonparallel chords. The shapes vary from 

 those higher at one end, as in Fig. 82 (a), to those approaching an 

 arch form as at (6). Part of the shear is carried by the sloping 

 chord. When the chord stress is found by one* of the preceding 

 methods it is the horizontal stress. For a sloping chord the hori- 



zontal stress must be multiplied by the inclined length and the 

 product divided by the panel length, the result being the axial 

 (longitudinal) stress in the inclined member. 



In the Warren truss (Fig. 83) the stresses in the web members 

 are alternately tension and compression, the light lines indicating 

 tension and the heavy lines compression. Each panel is an equi- 

 lateral triangle and in the figure the truss is a single system. By 

 using another set of triangles and placing the trusses side by side 

 so one triangle overlaps another by half the width, we obtain a 

 double system. Similarly, we may use a triple-system or a four- 

 system truss. When two or more systems are used the result is 

 a Latticed Truss, (Fig. 84). 



Let W = total load on the truss, uniformly distributed, 

 P = load on each triangle, 

 n = number of triangles in the primary single system. 



