# Columns 46

## column, axis, gyration, radius, fig and single

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COLUMNS 46. Strength of Columns. The strength of a column depends not only on its length and on the area of its cross-section, but also on the shape and position of the material in the column. The writer took a sheet of the paper on which this book is printed, and, holding it out straight, pressed down with it upon a scale. The scale registered pound when the paper crumpled. Another sheet was taken, and rolled into a tube Fig. 66. Showing Distribution of Areas in Compression Members.

% inch in diameter. The scale registered pounds before the paper crumpled. Again, sup pose that a column 12 feet long, consisting of a solid bar 4 by 4 inches=16 square inches in area, were used. The strength would be 159,360 pounds if designed according to the formula 17,100-57 l/r given in (C 141). Now, if the same amount of material were put into a column with cross-section by inches, and the sides were inch thick, the column would hold 253, 440 pounds, an increase in strength of 94,080 pounds, or nearly two-thirds of the original load. From this it will be seen that the farther away from the center of the column the material is lo cated, the stronger is the column. Fig. 66 shows the two sections.

Radius of Gyration. In picking out a col umn, it is important, for any given shape, to know how the area lies in regard to the distance from its center. This is given for different shapes, and is indicated by the radius of gyra tion.

a.

Y? =1.,5 rig. 67. rig. 68.