256 



STRESSES IN A HALF-HIP TRUSS. 



Art. 133. 



and the balance of the truss is like a Pratt. The coefficients 

 for the web members are gotten in the same manner as for a 

 Pratt and a Warren. It must be remembered that the secant 

 for the end diagonals is different from that for the intermediates. 



For the chord stresses the horizontal components are added 

 as in the preceding cases, but it must be remembered that the 

 tangent for the intermediate diagonals is double that of the end 

 diagonals, so that in adding the coefficients for the intermediate 

 diagonals they must be doubled; thus at joint 6, the coefficient 

 for 7 2 is 4 -f 2X1 =6. The tangent of the end diagonals is then 

 used in connection with all the chord coefficients. 



If the slope of the end diagonals is not exactly half that 

 of the intermediate ones, the chord coefficients will have to be 

 written in two parts, as 4P tan + 1P tan 6 f for C7 2 . 



3 L 2 1 



5 Equal Panels 



Fig. 187. 



Fig. 187 gives the coefficients for dead and live load, as- 

 suming all of the dead load as acting at the lower chord. 



134. Stresses in a Whipple Truss. The Whipple 

 truss is statically indeterminate (42), but it is usually assumed 

 that the two trusses into which it may be separated act inde- 

 pendently in transmitting the stresses (122). This assumption 

 is not true, as may readily be seen by considering a single load 

 at any point. Suppose a load is acting at joint 5, Fig. 188 (a). 

 According to the above assumption this would produce stresses 

 in the truss of Fig. 188 (b), but no stress in the truss of Fig. 188 (c) 

 except in the chords and end posts. But truss (b) cannot deflect 

 without causing deflection in truss (c) also. Therefore, the load 

 at joint 5 produces stresses in truss (c) as well as truss (b). (8.) 



According to the usual assumption the truss is separated 

 into two parts, Fig. 188 (/>) and (c), and the coefficients written; 

 then those for the members common to both trusses are added 

 and put on the original diagram, Fig. 188 (a). Each truss is 

 assumed to carry alternate panel loads. 





