434 PROBLEMS 



PROBLEM n. DEAD LOAD STRESSES IN A FINK TRUSS BY GRAPHIC 



RESOLUTION. 



(a) Problem. Given a Fink truss, span 6o'-o", pitch */$, camber 

 of lower truss 3'-o", trusses spaced i4'-o", load 40 Ibs. per sq. ft. of 

 horizontal projection. Calculate the reactions by means of force and 

 equilibrium polygons. Calculate the stresses by graphic resolution. 

 Scale of truss, i" = lo'-o". Scale of loads, i" = 5000 Ibs. 



(b) Methods. Start the truss at (0.75", 7.0"). Start the stress 

 diagram at (6.75", 6.25" ). Calculate the stresses as described in 

 Figs. 30 and 34, replacing the members 4-5 and 5-6, temporarily by the 

 dotted member shown. The stress diagram is then carried through 

 to the point 7, and then the stresses in members 5-6 and 4-5 are easily 

 obtained. Carry the stress diagram through and check at R 2 . 



(c) Results. The upper chord is in compression and the lower 

 chord is in tension, the stresses being practically the same as in the 

 triangular truss in Problem 9. In the webs it will be seen that the 

 long members are in tension, while the short members are in com- 

 pression. The loads coming on the reaction are not considered, as they 

 have no effect on the stresses in the truss, as can be seen by comparing 

 with the truss in Fig. 30. As a check the points i, 2, 5, 6, in the 

 stress diagram should be in a straight line. The dead joint load will be 

 equal to the horizontal projection of the area supported by a panel 

 point, multiplied by the dead load per square foot, is equal to 14 



X 40 = 4200 Ibs. 



PROBLEM ua. DEAD LOAD STRESSES IN A FINK TRUSS BY GRAPHIC 



RESOLUTION. 



(a) Problem. Given a Fink truss, span 6o'-o", pitch J^, camber 

 of lower truss 2'-o", trusses spaced i6'-o", load 40 Ibs. per sq. ft. of 

 horizontal projection. Calculate the reactions by means of force and 

 equilibrium polygons. Calculate the stresses by graphic resolution. 

 Scale of truss, i" '= lo'-o". Scale of loads, i" 5000 Ibs. 



