lujuuspoimu

Lujuuspoimu is a term used in structural engineering to describe a buckling mode in compression members where the critical load is governed by the material’s strength rather than by geometric stiffness. In practice, buckling occurs when the material yields or reaches its ultimate strength before the member loses lateral stability due to its shape or slenderness. This makes lujuuspoimu most relevant for relatively stocky members with low slenderness or for cross-sections and details that promote local yielding, such as thick-walled sections or plates where flange or web yielding can lead to global instability.

The concept is often contrasted with jäykkyyspoimu, or elastic (Euler) buckling, where the critical load is determined primarily by the member’s stiffness, length, and boundary conditions, and the material remains elastic at buckling onset. In lujuuspoimu checks, the design involves ensuring that the axial stress, possibly in combination with bending, does not reach the material’s yield or ultimate strength, often using interaction criteria that couple load and bending effects.

Recognizing lujuuspoimu helps identify capacity reductions due to material yielding, local or distortional effects, and post-buckling behavior. It can influence design choices such as cross-section shape and thickness or material selection to raise the strength-controlled capacity.

See also: Euler buckling, local buckling, plate buckling.