246 STRESSES IN PRATT TRUSS BY COEFFICIENTS. Art. 130. 



130. Stresses in a Pratt Truss by Coefficients. As 



was pointed out in Art. 127, it is convenient to use coefficients 

 in getting the stresses in trusses with parallel chords. For 

 the web members a coefficient represents a shear. The stress in 

 any web member is the shear at the section multiplied by the 

 secant of the angle which that member makes with the vertical. 



7 Equa/ Panels ~-+- 



Fig. 182. 



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If the member is vertical, its secant is one. The chord stresses 

 may be obtained by horizontal resolutions at the joints. Evi- 

 dently the vertical members have no horizontal components, 

 so the stress in any chord is made up of the sum of the horizontal 

 components of the diagonals between that chord and the end 

 of the truss. Therefore, the chord coefficients will be multi- 

 plied by sec OXsin 6 or tan 6, where 6 is the angle of the diag- 

 onal with the vertical. 



