This section is from the book "The Building Trades Pocketbook", by International Correspondence Schools. Also available from Amazon: Building Trades Pocketbook: a Handy Manual of reference on Building Construction.
The columns used in building construction are usually of stone, wood, cast iron, or structural steel. Stone columns are more frequently met with as features of architectural treatment than as supporting members of the structure. When they are used as structural members, they are generally so proportioned that they fail by crushing, and their strength depends on the compressive resistance of the material.
Wooden columns have their principal use in such buildings as large stores, factories, and warehouses, constituting part of a system of slow-burning construction which many consider to be superior to partially fireproof construction embodying cast-iron columns. The argument advanced is that, in case of fire, the wooden columns will become charred upon the outside, and, thus protected, the body of the column will retain its strength and successfully support the loads above; while under similar conditions cast-iron columns will become intensely heated, and, if water is played upon them, will snap and thus prematurely destroy the building. Cast-iron columns are rapidly being superseded by those built up of rolled-steel sections, or, as they are called, structural-steel columns. This is evidently due to the low price of structural steel, and also to the unreliability of cast iron under the action of fire and suddenly-applied loads. Another objection to cast-iron columns is the difficulty of making rigid connection between the columns of the several floors, and also of the floorbeams to the columns. This objection becomes serious when the height of the building increases to 8 or 12 stories; it is on record that, on account of this lack of rigidity in the connections, a certain building in New York was forced by the wind 11 inches out of plumb.
The strength of columns depends upon their length and shape of cross-section. Long columns will fail by bending under less load than will short columns. Of two columns having the same sectional area, the one having the material in the section distributed farthest from the central axis of the column will be stronger than one having the bulk of material located near the center.
If all the material composing the cross-section of a column could be located at a distance from the center equal to the radius of gyration, the column would possess equal strength to resist flexure as though the material was distributed over the cross-section. Hence, in formulas for calculating the strength of columns, both the radius of gyration and the length are to be taken into consideration.