STRUCTURAL COLUMN CURVES REFERENCE AND CIVIL ENGINEERING TUTORIALS

STRUCTURAL COLUMN CURVES BASIC REFERENCE
What Are Structural Column Curves?

Curves obtained by plotting the critical stress for various values of the slenderness ratio are called column curves. For axially loaded, initially straight columns, the column curve consists of two parts: (1) the Euler critical values, and (2) the Engesser, or tangent-modulus critical values.


Column curves: (a) stress-strain curve for a material that does not have a sharply defined yield pont: (b) column curve for this material; (c) stress-strain curve for a material with a sharply defined yield point; (d ) column curve for that material.

The latter are greatly affected by the shape of the stress-strain curve for the material of which the column is made, as shown in Fig. 5.44.

The stress-strain curve for a material, such as an aluminum alloy or high-strength steel, which does not have a sharply defined yield point, is shown in Fig. 5.44a.

The corresponding column curve is drawn in Fig. 5.44b.

In contrast, Fig. 5.44c presents the stress strain curve for structural steel, with a sharply defined point, and Fig. 5.44d the related column curve.

This curve becomes horizontal as the critical stress approaches the yield strength of the material and the tangent modulus becomes zero, whereas the column curve in Fig. 5.44b continues to rise with decreasing values of the slenderness ratio.

Examination of Fig. 44d also indicates that slender columns, which fall in the elastic range, where the column curve has a large slope, are very sensitive to variations in the factor k, which represents the effect of end conditions.

On the other hand, in the inelastic range, where the column curve is relatively flat, the critical stress is relatively insensitive to changes in k.

Hence the effect of end conditions on the stability of a column is of much greater significance for long columns than for short columns.

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