Rigidframe

A rigid frame, in structural engineering, is a structural system in which the joints between members are designed to transfer bending moments, making the connections moment-resisting rather than pin-connected.

As a result, each member develops bending moments and shear forces under lateral and vertical loads, and the frame acts as a continuous system distributing loads through bending rather than solely axial forces.

Rigid frames are common in steel and concrete constructions, including multi-story buildings and long-span frames such as portal frames, where moment connections at joints enable efficient use of material and provide stiffness against wind and seismic forces.

Design and analysis typically involve stiffness-based methods (matrix structural analysis) or finite element models to capture the distribution of moments and drifts. Joint details can be welded or bolted moment connections in steel, or reinforced concrete shear walls and beam-column interactions in concrete frames.

Compared with braced or pinned-frame systems, rigid frames offer greater lateral stiffness but can experience story sway and torsional irregularities if mass and stiffness are not well balanced; this requires careful detailing and sometimes supplementary bracing or shear walls.

In automotive engineering, a rigid-frame chassis refers to a single rigid structure forming the primary load-bearing member, used in contrast to unibody designs where the body and frame are integrated.