72 STRESSES IN BRIDGE TRUSSES 



Algebraic Moments. The dead and live load stresses in a truss 

 with inclined chords are calculated by algebraic moments in Fig. 48. 

 The conditions for maximum loading are the same in this truss as in 

 a truss with parallel chords, and are as follows: Maximum chord 

 stresses occur when all loads are on; minimum chord stresses occur 

 when no live load is on ; maximum web stresses in main members occur 

 when the longer segment of the truss is loaded ; and minimum stresses 

 in main members and maximum stresses in counters occur when the 

 shorter segment of the truss is loaded. An apparent exception to the 

 latter rule occurs in post U 2 L 2 which has a maximum stress when the 

 truss is fully loaded with dead and live loads. 





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y 



)/7 L-19.ZO ..Max-ZZ.OO . Max -22.~>f Q 



' L, naK-te.^o L, L, L| Ho 



2 Min-7.20 * l * 



MAXIMUM AND MINIMUM STRESSES 



IN 

 CAMELS BACK TRUSS 



BY 

 ALGEBRAIC MOMENTS 



Dead Load 3 Tons pr Joint 

 Live Load Q > 



FIG. 48. 



To find the stress in member U^ L 2 take moments about point A, 

 the intersection of the upper and lower chords produced. The dead 

 load stress is then given by the equation 



Ui L 2 x 70.7 + R x 60 W x 80 = o 



Ui'Lz x 70.7 = 6x6o + 3 x 8o = 120 foot-tons 



C7 L 2 = i . 70 tons 



