Engineering Reference

Effective length (K factor)

The length a column behaves as if it had, allowing for how its ends are restrained.

Definition

K converts actual length into the equivalent pinned-pinned length: 1.0 for pinned ends, 0.7 for fixed-pinned, 0.5 for fixed-fixed and 2.0 for a free end.

Because K is squared in the Euler formula, the difference between 1.0 and 2.0 is a factor of four in capacity. Real connections are never perfectly pinned or fixed, which is why codes give K values based on the actual joint stiffness.

Common misuse

Using K = 1.0 for every column. A cantilever or a fixed-base column has very different capacity, and the error is a factor of four.

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