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This buckling can be avoided, and the bars made mutually self-supporting, by means of the bands which are placed around the concrete column. These bands are usually 1-inch or 5-inch round or square bars. The specifications of the Prussian Public Works for 1904 require that these horizontal bars shall be spaced a distance not more than 30 times their diameter, which would be 712 inches for i-inch bars, and 111 inches for *-inch bars. The bands in the concrete column are likewise useful to resist the bursting tendency of the concrete column, especially when it is short. They will also reinforce the concrete column against the tendency to shear, which is the method by which failure usually takes place. The angle between this plane of rupture and a plane perpendicular to the line of stress is stated to be 60°. If, therefore, the band are placed at a distance apart equal to the smallest diameter of the concrete column, any probable plane of rupture will intersect one of the bands, even if the angle of rupture is somewhat smaller than 600. The unit working pressure permissible in concrete columns is usually computed at from 350 to 500 pounds per square inch. The ultimate compression for transverse stresses for 1:3:5 concrete has been taken at 2,000 pounds per square inch. With a factor of 4, this gives a working pressure of 500 pounds per square inch; but the ultimate stress in a concrete column of plain concrete is generally less than 2,000 pounds per square inch. Tests of a large number of 12 by 12- inch plain concrete columns showed an ultimate compressive strength of approximately 1,000 pounds per square inch; but such concrete columns generally begin to fail by the development of longitudinal cracks. These would be largely prevented by the use of lateral reinforcement or bands. Therefore the use of 500 pounds per square inch as a working stress for concrete columns which are properly reinforced may be considered justifiable although not conservative. It may be demonstrated by theoretical mechanics, that if a load is jointly supported by two kinds of material with dissimilar elasticity, the proportion of the loading borne by each will be in a ratio depending on their relative areas and module of elasticity. The formula for this may be developed as follows:  Example 1: A concrete column is designed to carry a load of 160,000 pounds. If the concrete column is made 18 inches square, and the load per square inch to be carried by the concrete is limited to 400 pounds, what must be the ratio of the steel, and how much steel would be required? Answer. A concrete column 18 inches square has an area of 324 square inches. Dividing 160,000 by 324, we have 494 pounds per square inch as the total unit compression upon the concrete and the steel, which is C in the above formula. Assume that the concrete is 1:3:5 concrete, and that the ratio of the module of elasticity (r) is therefore 12. Substituting these values in Equation 41, we have: Multiplying this ratio by the total area of the concrete column, 324 square inches, we have 6.93 square inches of steel required in the concrete column. This would very nearly be provided by four bars 1 inch square. Four round bars 11 inches in diameter would give an excess in area.  Either solution would be amply safe under the circumstances, provided the concrete column was properly reinforced with bands. A concrete column 16 inches square is subjected to a load of 115,000 pounds, and is reinforced by four 1-inch square bars besides the bands. What is the actual compressive stress in the concrete per square inch? Answer. Dividing the total stress (115,000) by the area (256), we have the combined unit-stress C = 449 pounds per square inch. By inverting one of the equations above, we can write: In the above case, the four -i-inch bars have an area of 3.06 square inches; and therefore, Substituting these values in the above equation, we may write: The net area of the concrete in the above problem is 252.94 square inches.

Are You in Carver Massachusetts? Do You Need Concrete Cutting?

We Are Your Local Concrete Cutter

Call 781-519-2456

We Service Carver MA and all surrounding Cities & Towns