CHAPTER V 



COLUMNS AND STRUTS 



81. Nature of compressive stress. When a prismatic piece of 

 length equal to several times its breadth is subjected to axial com- 

 pression it is called a column, or strut, the word " column " being us. 

 designate a compression member placed vertically and bearing a static 

 load ; all other compression members being called struts. 



If the axis of a column or strut is not perfectly straight, <>i if Un- 

 load is not applied exactly at the centers of gravity of its ends, a 

 bending moment is produced which tends to make the column d< 

 sideways, or "buckle." The same is true if the material is imt per- 

 fectly homogeneous, causing certain parts to yield more than t i 

 Such lateral deflection increases the bending moment, and e< 

 quently increases the tendency to buckle. A compression ineinl 

 therefore, in a different condition of equilibrium fnun one subj-- 

 to tension, for in the latter any deviation of the axis from a straight 

 line tends to be diminished by the stress instead of increased. 



The oldest theory of columns is due to Kulrr, and his fnrnni! 

 p still the standard for. comparison. Euler's thri.ry. Imw- 



ever, is based upon the assumptions that tin- mluiun is 



perfectly straight, the material perfectly 



and the load exactly centered at the ends, assump- 

 tions which are never exactly realized. I'"i j.ra-ti-al 

 purposes, therefore, it has been found nectary t< 

 modify Euler's formula in such a way as to l>rini: it 

 into accord with the results of actual experiments, as 



x_ explained in the following articles. 



82. Euler's theory of long columns. C msi.ler a long 

 FIG 78 c l umn subjected to axial loading, and assume that 

 the column is perfectly straight and homogeneous, and 

 that the load is applied exactly at the centers of gravity of its ends. 



