JOINTS AND CONNECTIONS 163 



carries all the load until the fibers give and then the other end 

 comes into bearing. The detail of (c) should never be used. It 

 has two end bearings and in addition has the sloping face which 

 is difficult to fit. If one, or both ends, compress through rotting 

 or crushing of the fibers, the load is carried on the sloping face, 

 which increases the tension on the bolts and hastens the destruc- 

 tion of the member. When splices are made in a top chord the 

 joints are preferably vertical, the views shown being top or bottom, 

 as may be desired. The number of bolts to use, and the sizes, 

 are matters determined by judgment and experience in the three 

 details shown. 



The detail at (d) is one commonly used when the piece under 

 compression is made of several pieces. The pieces should be as 

 thick as possible, and if more than one thickness is used use the 

 tli inner pieces inside and the thicker pieces on the outside. To 

 design such a member consider the load to be uniformly distributed 

 so that each piece carries a load proportionate to the area. If one 

 piece bends, part of the load it carries must be transferred to the 

 adjoining piece by shear, so shear pins are inserted at intervals 

 of 15 times the thickness of the thinner of the pieces. Divide the 

 total load by the number of planes between the pieces, that is, 

 by the number of pieces less one. This may be assumed to be 

 shear and it is divided by the number of shear pins in one joint to 

 determine the amount of bearing for each pin. From this the 

 bearing area may be ascertained in the manner shown for the shear 

 pin splice and the table fish-plate splice for tension members. The 

 bolts are close to the pins and are designed to take tension, the 

 amount of which is ascer- 

 tained from the moment 

 caused by the load carried 

 by the outer pieces. A 

 compression member, or 

 column, carefully designed tr-Hf- 





according to the above 



method, should be about . * 



95 per cent as efficient as 



a solid piece of the same outside dimensions. The ends should 



be carefully dressed to insure the load being uniformly carried by 



all the pieces. It is advisable to use a thin sheet of lead on each 



end of the member. 



