JOINTS AND CONNECTIONS 141 



shown in Fig. 87. One washer will bear on the side of the fibers 

 and the other washer will bear at an angle to the fibers. Using 

 the proper table giving the safe bearing strength of the wood 

 perpendicular to the fibers proportion the side bearing washer 

 accordingly. For the safe pressure to allow under the washer 

 set at an angle to the fibers, and also to determine the safe bearing 

 at the foot of the sloping member, several formulas have been 

 proposed. 

 The Jacoby formula is as follows: 



n = p sin 2 ^ + q cos 2 0, 



as given in his book " Structural Details." In Engineering News, 

 Vol. 68, Professor Malverd A. Howe published the result of some 

 tests made to determine the allowable bearing pressure on inclined 

 surfaces for various timbers, and recommended the formula 



n = q + (p - 5 



in which n = the allowable unit stress on a surface which makes 



an angle 6 with the direction of the fibers, 

 p = the allowable unit stress against the ends of the fibers, 

 q - the allowable unit stress on the sides of the fibers. 

 The author in attempting to simplify the formula of Professor 

 Jacoby and make it fit closer to some experiments on timber 

 other than yellow pine, which the Jacoby formula closely fitted 



a,t low angles, developed the following straight-line formula. 

 pa 



value equal to q. Straight line 80 to 90. 



Later, learning of the Howe formula, he attempted to simplify 

 it and developed the following formula: 



e ( e v 



n - fr-^f (77^) ' minimum value equal to q. 



U.ol \1UU/ 



In the two formulas of the author the angle 6 is expressed in 

 figures, as 10, 20, 30, etc. 



In Fig. 88 the four formulas are platted. The diagram appeared 

 in the July, 1916, Western Engineering, with the Jacoby and Howe 

 formulas, the author adding here the curves produced by his own 

 formulas. 



The student should now be able to determine the size and 

 number of nails, screws, lag screws, or bolts for all the joints of the 



