JOINTS AND CONNECTIONS 



175 



casting shown at (a). The position of the bolt is fixed by the size 

 of the washer at the upper end and by the necessity for having 

 the uncut portion of the block long enough to resist failure by 

 shear. The pins are shown square, but they may be round if 

 desired. From the examples given the student should have no 

 difficulty in designing a detail such as this. Supply enough pins 

 for bearing and enough space between them for shear. The ver- 

 tical bolts are in tension, but of course this tension is greatly re- 

 duced by the stiffness of the block, the thinner part of which 

 must have area enough to carry the tension in the end panel of 

 the chord. The lower washer must have area enough to keep 

 the pressure to the limit imposed by the angle at which the pres- 

 sure is delivered to the wood. 



In Fig. 103 is illustrated a cast-iron shoe. It may have slightly 

 different details, this being true of every design here illustrated. 

 The form shown is a rather com- 

 mon type. There are no diagonal 

 bolts, so the pressure on the top of 

 the chord is not uniform. A toe 

 projecting in front of the brace is 

 provided to take care of this. The 

 depth of the lugs is fixed by the end 

 bearing strength of the wood. The 

 thickness of the lugs is fixed by 

 their resistance to shear and bend- 

 ing, for they are short cantilevers 

 and are so designed. The spacing 

 of the lugs is governed by the 

 shearing strength of the timber 



U-- ...... 25" ...... 



Fig. 103. 



with the grain. The first lug is usually placed directly under the 

 end of the batter post. The arrangement of the ribs fitting into 

 the end of the batter post is much a matter of judgment. Cast 

 iron is a brittle metal and it is best to have the least thickness 

 more than half an inch. The thickness to use will usually be 

 determined by the size of the casting; a large heavy casting re- 

 quiring larger individual parts, should have all the parts thick, 

 because a fall will be more apt to injure it than a smaller casting. 

 Proceeding with the design. The wood at the end of the batter 

 post is not held by bolts, nor confined in a shoe, therefore a 

 reduced stress will be used. 



