178 



PRACTICAL STRUCTURAL DESIGN 



Depth of lugs = 



49 000 



= L915 iaB ' Use ^~' lugs * 



2i60(x8 

 Thickness of lugs for bending : 



Bending moment 'on one lug = 24,500 Ibs. X 1.5 = 36,750 in. Ibs. 

 Thickness of lug assumed to be 1 in. 



Required section modulus = ^-^ - n = 1.465. 



Required thickness of lug = 1.05 ins. Use 1-in. plate as assumed. 



49,000 



Length required for shear between lugs = 



2 x 150 x 8 



= 20.4 ins. 



Use 1 ft. 8.5 ins. 



Depth of toe = 



49,000 



3.84 ins. Use 4 ins. 



1600 x 8 



Bearing stress of 1600 Ibs. per sq. in. is used, as the timber 

 fibers are confined and therefore capable of taking full end com- 

 pression. 



Stress in bolster = horizontal component of stress in two f-in. 

 bolts = 4830 Ibs. x 2 x 0.5 = 4830 Ibs. 



No. of shear pins required = j -^ = 0.75. Use one 2-in. pin. 



.In the cast-iron shoe shown in Fig. 103 the projection of the 

 toe limited the bearing stress on the top of the chord. In the 

 form shown in Fig. 104, since the line of thrust intersects the shoe 

 practically at the end of the toe, the inclined bolts will be called 

 into play to prevent a rotation of the shoe, which would greatly 



increase the toe pres- 

 sure. The bolts, there- 

 fore, must be always 

 tight in order to 

 secure an approxi- 

 mately uniform ver- 

 tical pressure. 



This form of joint 

 is considered very 

 good because it is 

 simple in action and 



IBentPt. f&tf&fefr* 



aUunfrnf 



%" Countersunk Rivets ca. Tab. 



6"x8"Bofsfer 8, s /g 'Bo/fs 

 '* 3 %x3lftbsh*rs 10, %x3%x 3% Washers 

 Hill Bearing Edge of Tables. 



Fig. 105. 



comparatively easy to frame into the timber. Both lugs must 

 have an even bearing against the wood and this is a hard thing 

 to secure, but if the inspection is good the work will be all right. 

 When there is more than one bearing surface this objection 



