144 PRACTICAL STRUCTURAL DESIGN 



strong enough to carry half the load, which will maintain the 

 integrity of the joint in case the cleats through shrinkage, or decay 

 of dap, lose one-half their strength. To prevent the braces from 

 being pushed off to one side they may be nailed to the cleats or 

 a thin strip of iron may be inserted in a saw cut, one-half in the 

 cleat and one-half in the foot of the brace. 



At ( j) is shown a method often used in making a joint at the 

 foot of a raking member. The vertical bolts are assumed to resist 

 the thrust. It is a poor joint. The habit of many draftsmen is 

 to guess at the number of bolts, and they seldom add additional 

 area to supply that lost in the bolt holes. A better joint is shown 

 at (fc). The black circles are the ends of pipes used as shear pins. 

 They are designed to take all the thrust and the joint is made by 

 spiking the two pieces together, after which the bolt holes are 

 bored and the bolts driven and tightened. Enough bolts should 

 be used to take half the tension in the lower chord; as direct 

 tension, not cross bearing. After the bolts are tightened the spike 

 can be removed and holes bored for the pins which are then 

 driven through. 



In making joints in woodwork study the problem carefully. 

 Avoid pockets where moisture may collect. Cracks seriously weaken 

 timber framework, and as cracks usually start from interior angles 

 all complicated framing joints should be avoided. Frame all pieces 

 so the center lines through stressed areas will meet at a common 

 point and try to make all jointing lines straight. Jogs in joints 

 not only are apt to start cracks, but there is a danger of shrinkage, 

 causing unequal bearing, which will set up bending moments 

 about the joint, so it is best to have straight joints which admit of 

 adjustment. If through any mischance the two faces do not meet 

 perfectly, insert a thin sheet of lead, which, in course of time, will 

 equalize the bearing. Engineering principles were seldom used 

 for timber joints in former generations, much of the work being 

 done by carpenters who had no engineering training and by drafts- 

 men who blindly copied old examples. Design the joint in accord- 

 ance with engineering principles, not forgetting that wood shrinks 

 and that when moist it rots. The joint is bound to be all right if 

 it is simple and the computations show it to be adequate for the 

 work it must do. 



In studying joints of members they are considered as single 

 sticks. Methods for making single sticks out of a number of pieces 



