JOINTS AND CONNECTIONS 179 



always arises. If the fitting is not properly done the joint can 

 be shimmed with thin metal shims. 



Mr. Dewell makes the following comments: "This shoe can 

 be used only for stresses requiring not more than two lugs, hence 

 its field of application is limited. Another defect is that the 

 forge work is difficult with the thickness of plate used. Especially 

 is this true of the bending of the end of the inner plate to form 

 the inner lug. Incidentally, this detail forms a good example of 

 the consideration of actual unit working stresses as compared 

 with purely theoretical values, as mentioned in the first article 

 of this series. With a 2-in. depth of lug, the bearing pres- 

 sure against the ends of the fibers is assumed to be 1600 Ibs. 

 per sq. in. On account of the fillet formed in bending 

 the plate, the actual bearing area will be decreased and the 

 actual unit working stress will probably be around 1800 Ibs. per 

 sq. in." 



In Fig. 104 and Fig. 105 the sizes of the two diagonal bolts are 

 determined by judgment and experience. They are not suscep- 

 tible of computation. The vertical bolts are found by computa- 

 tion. When any computation is omitted in any of the examples 

 it is for the reason that the student is assumed to know how to 

 make it. Every detail must be investigated according to the 

 principles and methods illustrated. 



Fig. 105 is a modification of Fig. 104. Steel tables rivetted to 

 the plate are substituted for the lugs used in Fig. 104. The forge 

 work is less; any number of tables may be used; and the main 

 plate may be reduced to a thickness determined by considera- 

 tion of shear and tension alone. In Fig. 104 the plate thickness 

 is determined by the thickness required of the lug to prevent it 

 straightening under load. No table should be placed under the 

 foot of the batter post, for the seat for the table is usually cut a 

 little deeper than the table, so the full bearing area under the 

 post will not be obtained with a table under it. 



The computations for Fig. 105 are as follows : 



Depth of toe as in Fig. 104, 4 in. 



Area required for bearing between upper and lower chord 

 28,125 



A 10-in depth will, therefore, be required for the upper chord, 

 giving an area of 8 X 13 ins. - 104 sq. ins. 



