45 PROBLEMS 



PROBLEM 19. DEAD LOAD STRESSES IN A HOWE TRUSS BY GRAPHIC 



RESOLUTION. 



(a) Problem. Given a Howe truss, span i6o'-o", panel length 

 2o'-o", depth 24'-o", dead load 600 Ibs. per lineal foot of truss. Calcu- 

 late the dead load stresses by graphic resolution. Scale of truss, i" = 

 25'-o". Scale of loads, i" = 15,000 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^ and checking at R 2 , following the order 

 shown in the stress diagram. 



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

 chord is in tension as in the Warren truss. All inclined web members 

 are in compression, while all vertical web members are in tension. The 

 stresses in the verticals are equal to the vertical components of the 

 diagonal members meeting them on the unloaded chord. Stresses in 

 certain panels in top and bottom chords are equal. 



The Howe truss is commonly built with timber upper and lower 

 chords and diagonal struts, the only iron being the vertical ties and cast 

 iron angle blocks to take the bearing of the timber struts. This makes 

 a very satisfactory truss and is quite economical where timber is cheap. 



PROBLEM 193. DEAD LOAD STRESSES IN A HOWE TRUSS BY GRAPHIC 



RESOLUTION. 



(a) Problem. Given a Howe truss, span i62'-o", panel length 

 i8'-o", depth 24'-o", dead load 600 Ibs. per lineal foot of truss. Calcu- 

 late the dead load stresses by graphic resolution. Scale of truss, i" = 

 25'-o". Scale of loads, i" = 15,000 Ibs. 



