CHAPTER X 
COLUMNS AND STRUTS 
154, Columns and Struts.—A Column or Pillar is always vertical, 
and generally it is fixed rigidly at its ends. A Strut may be vertical or 
inclined, and one or both ends may be fixed rigidly, or one or both ends — 
may be connected to the surrounding structure by flexible joints. The 
theory of struts will therefore evidently apply to columns. In most cases 
the only important load on a column or strut is one acting at its ends in 
the line of its axis and tending to shorten it. In some cases, however, 
there is a lateral load in addition. | 
Comparing a strut with a tie (Figs. 228 and 229), it is evident that 
if the strut and tie be bent by lateral forces or if they be originally bent, 
the load P on the strut tends to bend it still further, while the load P on 
OS ee 
PLO STRUT <o}? ’( sro}? 
Fig. 228. Fig. 229. 
the tie tends to straighten it. The theory of a tie is obviously very 
simple, being expressed by the equation P= Af, where A is the area of 
the cross section and f the stress. The theory of the strut would be the 
same as that of the tie if the strut did not bend. Neglecting for the 
present the case of the laterally loaded strut, the load at its ends may 
bend the strut, because (1) the strut may not be perfectly straight when 
unloaded, (2) the load may not be applied exactly in the line of the axis — 
of the strut, and (3) through a want of uniformity in the material one 
part may yield more than the other parts in compression. 
The tendency of the strut to bend will evidently be greater the 
greater the ratio r of its length to its least transverse dimension, and 
the manner in which it gives way under the load will depend largely on 
the value of 7. When r is small there is no bending, and the strut gives 
way by crushing (or oblique shearing, as described in Art. 166, p. 175). 
When 7 is very large the strut gives way by bending, and for moderate 
values of 7 the strut may give way by crushing and bending. 
155. Critical Load for Long Column.—A simple and instructive — 
experiment on the behaviour of a long column will here be described. — 
A long slender lath of wood or a straight strip of steel is placed in a 
vertical position and loaded, the load being guided vertically, as shown in 
_ Fig. 230. The ends of this experimental strut are rounded and fit into 
shallow grooves in the end connections, as shown on an enlarged scale 
162 
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