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Plastic hinge versus elastic hinge

Short answer

A plastic hinge is a yielded section where moment equals Mp and rotation occurs at constant moment; an elastic hinge is a real pin carrying zero moment. A plastic hinge forms by yielding at maximum moment, transmits Mp, and locks on unloading, while an elastic hinge is a fixed zero-moment connection.

Define plastic hinge. Also compare plastic and elastic hinges of a structural system.

A plastic hinge is a section at which the bending moment has reached the plastic moment MpM_p, the whole section has yielded, and the member rotates at a constant moment MpM_p (like a hinge that still transmits the moment MpM_p). An elastic (ordinary) hinge is a real pin in the structure: it cannot transmit any moment.

PointElastic (ordinary) hingePlastic hinge
Moment carriedZeroConstant, equal to MpM_p
CauseProvided by construction (a pin or a connection)Formed by yielding of the section when M=MpM = M_p
RotationFree, in either directionOnly in the sense of the applied moment; locks when the moment reverses/unloads
PositionFixed, chosen by the designerLocated at points of maximum moment, depends on the loads
LengthZero (a point)Finite zone of yielding (hinge length)
Behaviour on unloadingNot affectedElastic recovery; the hinge becomes a rigid section again
Effect on the structureReduces the degree of indeterminacy by 1Also reduces the indeterminacy by 1, and the structure becomes a mechanism when enough hinges form

✓ Answer checked by Claude Opus 5.5 (high effort)

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