JOINTS AND CONNECTIONS 173 



by the thrust of the brace against the chord, or it must all be 

 carried by the bolts. 



In Fig. 101 is illustrated a low-cost end joint. A bolster is 

 placed on top of the lower chord and pins are used to transfer 

 the stress by shear, 2-in. pins being used. There may be unequal 

 shrinkage in the chord and bolster which will interfere with the 

 proper action of the round pins, so it is better to omit the pins 

 and use a bolster large enough to permit it to lock into the top 

 of the chord as a tabled fish-plate. The vertical bolts carry one- 

 half the tension and the method to use in figuring the size of the 

 bolts has been presented. 



This joint is designed as follows: Using an 8 in. X 10 in. bolster 

 the depth below the bottom of the cut will be 4.34 ins. Deduct 

 8 sq. ins. for the half pins and f x 4.34 ins. for the bolt holes, leaving 



25 000 

 an area of 23.47 sq. ins. The tensile stress will be ' = 1065 Ibs. 



Zo.Qi 



per sq. in., and the allowable safe fiber stress is 1600 Ibs. per sq. in. 

 Therefore the 8 in. x 10 in. bolster is O.K. 



nr 



Uncut projection for shear = ^ -^ = 26 ins. 



o X l^U 



The compression on the round pins will be taken at 800 Ibs. 



per sq. in. The required number of 2-in. pins = ^ = 3.9. 



o X o(X) 



Use 4 pins. 

 The thickness of bolster back of the brace required for ten- 



25 000 

 8 i n " 6 Tarn = 2 ins - The thickness is 4.34 ins. less 1 in. for 



o X loUU 



the pins - 3.34 ins., so this is O.K. 



The stress per pin = - - = 6250 Ibs. 



6250 

 The clear space between pins - 5 '- ^ - 6.5 ins. 



o X 



Sometimes a detail similar to that shown in Fig. 100 is used, 

 but instead of two bolts one is used. In the case considered this 

 bolt will be 'JJ -in. diameter. Instead of making a triangular cut 

 in the bottom of the chord to form a bearing surface for the washer, 

 a casting is used at the bottom for the lower end of the bolt. It 

 is very common to use such washers without computing the size 

 necessary, and in many existing trusses this detail is weak. The 

 computations are as follows, referring to Fig. 102 (a) : 



