404 CAMBRIA STEEL. 



Rectangular Wooden Beams gives a coefficient of deflection, by 

 means of which the deflection for any beam may be obtained, 

 corresponding to the given span and safe load, by dividing the 

 coefficient by the depth of the beam in inches, which will give 

 approximately the deflection in inches under the given conditions. 



In each table the deflection coefficient is given for only one 

 species of wood, as shown, but the deflections for other species 

 may be obtained from these by proportion as explained hereafter. 



For the reason that wood has no well-defined limit or modulus 

 of elasticity the deflections obtained by the use of the coefficients 

 are only approximate and will vary, according to the moisture 

 content of the wood and the character of the loading. The 

 deflections thus obtained are, therefore, useful only as a general 

 indication of the amount of bending to be expected under the 

 given conditions and are not exact as in the case of materials like 

 steel, which has a well-defined limit and modulus of elasticity.* 



The safe loads for other species of woods than those stated in 

 the headings of the tables may be obtained from those given, by 

 direct proportion, dependent upon the ratio of their allowable 

 unit stress as compared with that for which the table is figured, 

 as stated in the foot-notes at the bottom of the tables. 



* NOTE. "A series of tests, undertaken at the College of Forestry at Cornell 

 University, seems to demonstrate that, at least in coniferous wood, a definite 

 elastic limit for any particular piece can be easily shown, and, that it coincides 

 with the theoretically calculated elastic limit upon the bases of compression 

 tests and their application, according to Neely's formula." 



Explanation of the Table of Safe Loads for Rectangular 



Beams of White Pine, Cedar, Spruce or 



Eastern Fir. 



The values for the various species of woods, which are included 

 in this table are calculated for an allowable fibre stress, for 

 flexure, of 700 pounds per square inch. 



The deflection coefficients are given for white pine and are based 

 upon a modulus of elasticity of 1 000 000 pounds per square inch. 



The lower dotted line crossing the table indicates the limits of 

 spans for which the deflection will exceed ^^ of the span for the 

 kind of wood for which the deflection coefficient is given. For 

 spans below the line the safe loads given in the tables will produce 

 a deflection greater than ^^ of the span, while those above the 

 line will produce less than this, which is the usual limit of deflec- 

 tion in order to prevent cracking of plastered ceilings. Similarly, 



