JOINTS AND CONNECTIONS 



169 



The tensile stress 



464,500 



2807 Ibs. per sq. in., and the 



4 x 41.36 



allowable stress is 1600 Ibs. per sq. in., therefore the center line 

 of the support cannot 

 be so far from the 

 end of the brace. The 

 proper position, in or- 

 der to keep all forces 

 in equilibrium, is 5.42 

 ins. left of the bottom 

 point of the end piece. 

 The tension caused by 

 moving the support 

 farther to the left 

 must be added to the 

 tension in the chord; 

 so the actual stress, if 



Fig. 99. 

 (41.36 x 2807) + 25,000 



the support is away at the end, 

 141,098 Ibs. 



In Fig. 99 is shown another method of forming the joint, the 

 toe cut not being perpendicular (normal) to the line of thrust. 

 The angle at the toe is 75 degrees and the angle of the sloping 

 bottom of the cut is 16 degrees; for the angle between the sur- 

 faces may vary, it not being necessary to have the lower point 

 a right angle. Computations will be made to obtain the area of 

 the pressed surface and the allowable and actual pressures on the 

 surfaces. The computations for obtaining the projecting length 

 of the chord for shear will not be made, for it is like the work 

 done in the detail shown in Fig. 98. 



Depth of toe: 6 = 75 degrees, n = 1200 x 0.75 = 900 Ibs. per sq. in. 



35,950 



Required area in bearing 



40 

 Required depth of toe - -j 



o 



900 

 = 5 ins. 



40 sq. ins. 



This depth is too great for the lower chord, for if it is used the 

 depth of the chord must be increased, which will increase the weight 

 and be an uneconomical proceeding. We will therefore abandon 

 this type of joint for the truss, but the computations will be carried 

 through, merely as a problem, in order to show how the two bear- 

 ing surfaces affect the position of the center line of the support. 



