200 



RESISTANCE OF MATERIALS 



302. The testing machine shown in Fig. 145 is designed for a maximum load on 

 the platform of 100,000 Ib. The dimensions of the various levers are as shown in 

 Fig. 146, the lever C being V-shaped, with the lever D hung inside. Neglecting the 



Extreme position 

 of Weight - 



Plan, levers C and. D 



FIG. 146 



weights of the arms, compute the weight of the slider when in its extreme posi- 

 tion required to balance a load of 100,000 Ib. on the platform. 



303. Determine analytically the stresses in the members C.D, DE, and EF of 

 the curved-chord Pratt truss shown in Fig. 147, assuming the load at each panel 



point to be 50,000 Ib. 



/ 304. The roof truss shown in 



Fig. 148 is anchored at one end A, 

 and rests on rollers at the other 

 end B. The span I = 80 ft., rise 

 h = 30 ft., distance between trusses 

 6 = 18 ft. The weight of the truss 

 is given approximately by the for- 

 mula W = 2*4 bl' 2 ; the wind load, as- 

 sumed to be from the left, is taken 

 as 451b./ft. 2 of roof surface, and 

 the snow load is 30 lb./ft. 2 of hori- 

 zontal projection. Calculate analyt- 

 ically the reactions of the supports 

 due to all loads acting on the truss. 



305. In the saw-tooth type of 

 roof truss shown in Fig. 149, deter- 

 mine analytically the stress in FH. 



306. In the Pratt truss shown in 

 Fig. 150, the dimensions and loads 



are as follows : span = 150ft., height = 30ft., number of panels = 6. The dead 

 load per linear foot in pounds for single-track bridge of this type is given by the 

 formula w = 5 1 + 350, where I denotes the span in feet ; the weight of single track 



FIG. 147 



FIG. 148 



