10 



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. 

 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 calcinated for an allowable liber 

 stress, for flexure, of 700 Ib. per square inch. 



The deflection coefficients are given for white pine, and 

 are based upon a modulus of elasticity of 1,000,000 Ib. per 

 square inch. 



The lower dotted line crossing the table indicates the 

 limits of spans for which the deflection will exceed 1-360 of 

 tne span for the kind of wood for which the deflection 

 coefficient is given. For spans below the line the safe 

 loads given in ine tables will produce a deflection greater 

 than 1-360 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, the upper dotted line indicates the limit of de- 

 flection for the kind of wood for which the deflection 

 coefficient is given, corresponding to a modulus of elas- 

 ticity of 500,000 Ib. per square inch, which should be 

 considered in cases where the deflection should be more 

 closely limited. 



The coefficient of deflection for cedar corresponding to 

 moduli of 700,000 and 350,000 may be obtained by multiply- 

 ing those of the table by 10-7 and 20-7 respectively, and 

 for spruce and eastern fir corresponding to moduli of 

 1,200,000 and 600,000 by multiplying those of the table by 

 5-6 and 5-3 respectively. 



The full zig-zag line in the table gives the limits of the 

 safe loads corresponding to the allowable shearing stress 

 itlong the neutral axis of the beam. The safe loads above 

 the line, which are based upon the extreme fiber strains, 

 will produce shearing stresses along the axis or with the 

 vi a in in excess of that allowable, which, in the case of 

 white pine and the other woods of this table, is 100 Ib. 

 per sq. in. 



The position of this line, which indicates the limit of 

 safe loads for shearing along the neutral axis, was deter- 

 mined by the aid of the following formula: 



