STRUCTURAL TIMBER 



61 



When the length of the column exceeds 15d the above values, 

 given for " Compression with grain," shall be reduced as follows: 



S=c- 



cl 

 60cT 



where S = allowable working stress per square inch ; 

 C =" compression with grain " given above; 

 / = unsupported length of column in inches; 

 d= least width of column in inches; 



and maximum -7= 45. 



276. Timber in Railroad Bridges and Trestles. The max- 

 imum stresses due to the combined effect of dead and live loads, 

 lateral and longitudinal forces, including bending and impact, 

 shall not exceed the following values in pounds per square 

 inch. 



For columns whose length does not exceed lod the above 

 values, given for " Compression under 15 diameters," may be 

 used. 



When the length of the column exceeds 15d the above values, 

 given for " Compression with grain/' shall be reduced as follows: 



50dl 



