Compression Members

Compression members (such as columns, struts, and truss chords) are structural elements subjected primarily to axial compressive forces. Unlike tension members, which generally fail only by material yielding or fracture, compression members face the additional critical failure mode of instability, known as buckling. The behavior of a compression member is dictated by its slenderness ratio (KL/r). 1. Short, stocky columns fail by material crushing or yielding. 2. Long, slender columns fail by global elastic buckling (Euler buckling), where the member laterally deflects at a stress well below the material's yield strength. 3. Intermediate columns fail by inelastic buckling, a complex interaction of partial yielding (due to residual stresses from manufacturing) and geometric instability. Key engineering parameters include: - Unbraced Length (L): The distance between structural bracing points that prevent lateral translation. - Effective Length Factor (K): A coefficient that modifies the actual length based on the rotational and translational boundary conditions at the member's ends. - Radius of Gyration (r): A geometric property of the cross-section (r = √(I/A)). Columns will always buckle about their weakest axis (minimum 'r') unless braced otherwise. - Local Buckling: A failure mode where an individual slender element of the cross-section (like a thin web or flange) buckles before the overall member fails. Cross-sections are classified as compact, non-compact, or slender based on their width-to-thickness ratios.