JOINTS AND CONNECTIONS 181 



in the wood to a diameter a trifle less than the diameter of the 

 shank of the screws at the base of the threads. The lag screws 

 are to be screwed, not driven, into place. Bolts should not be 

 used, for it would be next to impossible to fit the plates so the 

 holes will all be hi line. To make a fit the bolts would require 

 some bending and thus much of their value in shear would be lost. 



"This type of end detail is well suited to trusses of an A 

 shape, resting upon posts. The side plates in such cases may be 

 extended to engage the top of the post, and thus to give consid- 

 erable stiffness to the building frame." Dewell. 



Computations for Fig. 106. 



Number of lag screws in upper chord = ,' = 47. 



49 000 

 Number of lag screws in lower chord = ..' = 41. 



Thickness of plate = fV m - 



Intermediate Joints in Trusses 



Intermediate joints in trusses must follow the general rule for 

 joints hi wood, that the carpenter work must be as simple as possible. 



The condition must be satisfied that the center lines of all 

 members must meet at a common point. In nearly all joints of 

 the types shown in Fig. 107 and Fig. 108 it often happens that 

 when all the center lines 

 meet at a common point 

 the hole for the rod will cut 

 away a part of the strut, 

 or the toes of the struts 

 will l>ear against the rods. 

 Sometimes this condition 

 cannot be avoided if the 

 strut is to be dapped into Fi - 107 - 



the chord. Quoting again from Dewell : "If it so happens that 

 the rod has not a driving fit in the chord, which condition will 

 usually exist, especially with an upset rod and a deep chord, the 

 toe of the strut will have bearing against the chord for only part 

 of its width. The result of this condition will be that the actual 

 bearing area may not be over one-half of what was assumed hi 

 design, and the unit-bearing stress may consequently be double 

 the allowable." 



