The columns used in skeleton construction are generally made up of a combination of the standard shapes of steel bars. One of the commonest forms of steel column is the Z-bar column, shown in Fig. 196. This column is made by bolting together four standard Z-bars with reinforcing plates, the bars and plates increasing in size and thickness as the loads to be supported increase. The column shown in Fig. 196 is of the type known as "closed columns" and can be used only where there is no necessity for repainting the steel, as only the outside surfaces are accessible. The open form of column, Fig. 197, is more generally used. Other forms of steel columns are formed from standard beams, Fig. 198, or from channels and angles, Fig. 199. As these columns will be required to support a heavy load in most cases, bases must be used which will distribute the weight over a surface large enough to sustain the load. This may be done by the use of a cast-iron base, Fig. 200, or a base built up of steel, Fig. 201.

Fig. 196. Closed Z bar Column.

Fig. 196. Closed Z-bar Column.

Fig. 197. Open Z bar Column.

Fig. 197. Open Z-bar Column.

Fig. 198. Steel Beam Column.

Fig. 198. Steel Beam Column.

Fig. 199. Channel and Angle Column.

Fig. 199. Channel and Angle Column.

The selection of a particular form of column section will depend upon varying conditions, being generally determined by the amount of load and the way in which the floor beams come to the column. The shape and size desired for the finished column, the thickness and detail of enclosing piers, and the availability of certain shapes, are also factors.