JOINTS AND CONNECTIONS 177 



This fixes the clear distance between lugs at 13 ins. and the 

 front lug will be set not less than 13 ins. from the end of the lower 

 chord. The end of the shoe will extend 2 ins. beyond the rear lug. 

 This makes the total length of the shoe, L = 25 ins. 

 Let a = distance from front lug to toe of shoe. 

 L - length of shoe. 



q = maximum pressure in Ib. per sq. in. at front edge of toe. 

 vertical reaction 35,950 



width of chord 2x8 



. ., 



_/_ 3a\ P / 3 X 8.5\ 2242 

 Then q = 2(2 - j-) j- = 2(2 - -^-J x -^- = 176 Ibs. 



which is well within allowable stress. 



The thickness of the lugs is determined by treating them as 

 cantilevers. The depth is 1.5 ins. loaded uniformly with 12,500 Ibs. 



The bending moment = f- 75 + 1 - 5> \ x 12,500 = 14,080 in. Ibs. 



The moment of resistance of a rectangular section, M r = Rbd 1 . 



The compressive stress of cast iron is 10,000 Ibs. per sq. in. and 

 the tensile stress is 3000 Ibs. per sq. in. A mean of these values 

 may be used in determining the resisting moment, but it is better 

 to use the tensile stress, and R = 3000 -$- 6 - 500. Then 

 14,080 



- 1.88 in. (make it 2 ins.). 

 o(JU X o 



Moment of rotation of lugs = bending moment on lug = 14,080 

 in. Ibs. Tension in bolt back of lug = ,~ * ,. = 5120 Ibs. Use 



one J-in. bolt. 



Figures 104, 105, and 106 are reproduced from an article by 

 Henry D. Deweil in 

 Western Engineering for 

 September, 1916, the 

 fourth in the valuable 

 series referred to. 



The computations for 

 Fig. 104 are as follows: 



Area required for bear- 

 ing between upper and Wafers' 



sq. ins. (Mr. Deweil used side bearing stress of 285 Ibs. per sq. in.) 



