444 PROBLEMS 



PROBLEM 16. DEAD LOAD STRESSES IN A CANTILEVER TRUSS BY 

 GRAPHIC RESOLUTION. 



(a) Problem. Given the Fink cantilever truss, span 4o'-o", depth 

 i2'-o", joint load 2000 Ibs. Calculate the reactions by means of force 

 and equilibrium polygons. Calculate the stresses by graphic resolution. 

 Scale of truss, i" = 8'-o". Scale of loads, i" = 1500 Ibs. 



(b) Methods. Calculate the reactions as in Fig. 16, page 30, 

 noting that the loads in the two cases are laid off in different order. 

 Note that the two reactions and the resultant of the external loads meet 

 in a point, and that the reactions can be determined by means of this 

 principle. The stress diagram is started with the load P and is closed 

 at R! and R 2 . 



(c) Results. The upper chord is in tension, while the bottom 

 chord is in compression, which is the reverse of conditions in simple 

 trusses. In calculating the stresses due to wind load in this truss, the 

 reaction R 1 will be in the line of 7-4, and R 2 will pass through A, as 

 in the case of dead loads. The resultant of the wind loads and the two 

 reactions will meet in a point, and the solution is essentially the same 

 as for dead loads. It should be noted that the closing line of the 

 equilibrium polygon, A-a, has its ends on the line of action of the 

 resultants R and R 2 . 



PROBLEM i6a. DEAD LOAD STRESSES IN A CANTILEVER TRUSS BY 

 GRAPHIC RESOLUTION. 



(a) Problem. Given the Fink cantilever truss, span 5o'-o", depth 

 I 5'-"> joint load 2500 Ibs. Calculate the reactions by means of force 

 and equilibrium polygons. Calculate the stresses by graphic resolution. 

 Scale of truss, i" = 8'-o". Scale of loads, i" = 2OOO Ibs. 



