454 PROBLEMS 



PROBLEM 21. DEAD LOAD STRESSES IN A CAMEL-BACK TRUSS BY 

 GRAPHIC RESOLUTION. 



(a) Problem. Given a camel-back (inclined Pratt) truss, span 

 i6o'-o", panel length 2o'-o", depth at the hip 2$'-o", depth at the 

 center 32'-o", d^ad load 400 Ibs. per lineal foot per truss. Calculate 

 dead load stresses by graphic resolution. Scale of truss, i" =2$'-o". 

 Scale of loads, i" = 10,000 Ibs. 



(b) Methods. The loads beginning with the first load on the left 

 are laid off from the bottom upwards. Calculate the stresses by graphic 

 resolution, beginning at R 1 and checking at R 2 . Follow the order 

 given in the stress diagram. 



(c) Results. The top chord is in compression and the bottom 

 chord is in tension. All inclined web members are in tension; while 

 part of the posts are in tension and part are in compression. Member 

 1-2 is simply a hanger and is always in tension. This type of truss is 

 quite generally used for steel and combination bridges for spans from 

 150 feet to 200 feet, and also for roof trusses for long span, where it 

 is loaded on the top chord and bottom chord, or on the top chord alone. 



PROBLEM 2ia. DEAD LOAD STRESSES IN A CAMEL-BACK TRUSS BY 

 GRAPHIC RESOLUTION. 



(a) Problem. Given a camel-back (inclined Pratt) truss, span 

 i8o'-o", panel length 2o'-o" (three panels with parallel chords), depth 

 at the hip 25'-o", depth at the center 32'-o", dead load 400 Ibs. per 

 lineal foot per truss. Calculate dead load stresses by graphic resolu- 

 tion. Scale of truss, i" = 25'-o". Scale of loads, i"= 12,000 Ibs. 



