Strength of Materials. 337 



Breaking load = = 10)800 lbs . 



What is the breaking load for the same 10 feet long? 14 

 feet long ? 16 feet long ? 18 feet long ? Solve the same prob- 

 lems for other woods. 



410. General Statements regarding the Quiescent Breaking 

 loads of Uniform Horizontal Beams, If the center quiescent 

 breaking load be taken as 1, then, when all dimensions are 

 the same, to find the breaking load: 



(1) When the beam is fixed at both ends and evenly 

 loaded throughout its whole length, multiply the result 

 found by (409) by two. 



(2) When fixed at only one end and loaded at the other, 

 divide the result obtained by (409) by four. 



(3) When fixed only at one end and the load evenly 

 distributed divide the result obtained by (409) by two. 



(4) To find the breaking load of a cylindrical beam, first 

 find the breaking load of a square beam having a thickness 

 equal to the diameter of the log and multiply the result by 

 the decimal .589. 



411. Breaking Load of 

 Rafters. In finding the 

 breaking load of timbers 

 placed in an oblique posi- 

 tion, as shown in Fig. 

 146, take the length of the 



raftcr equal to the hori- FIG. 



zontal span A, C, and pro- 

 ceed as in (409) and (410). 



412. Table of Safe Quiescent Center Loads for Horizontal 

 Beams of White Pine Supported at Both Ends. In this table 

 the safe load is taken at one-sixth of the theoretical break- 

 ing load. This large reduction is made necessary on account 

 of the cross-grain of timbers and joists and the large knots 



