In the
structural engineering
Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and muscles' that create the form and shape of man-made structures. Structural engineers also must understand and cal ...
beam theory
Beam may refer to:
Streams of particles or energy
*Light beam, or beam of light, a directional projection of light energy
**Laser beam
*Particle beam, a stream of charged or neutral particles
**Charged particle beam, a spatially localized grou ...
, the term "plastic hinge" is used to describe the deformation of a section of a
beam
Beam may refer to:
Streams of particles or energy
*Light beam, or beam of light, a directional projection of light energy
**Laser beam
*Particle beam, a stream of charged or neutral particles
**Charged particle beam, a spatially localized grou ...
where
plastic bending Plastic bending is a nonlinear behavior particular to members made of ductile materials that frequently achieve much greater ultimate bending strength than indicated by a linear elastic bending analysis. In both the plastic and elastic bending ana ...
occurs. In
earthquake engineering plastic hinge is also a type of energy
damping
Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples in ...
device allowing
plastic
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...
rotation
eformationof an otherwise rigid column connection.
Plastic behaviour
In plastic
limit analysis Limit analysis is a structural analysis field which is dedicated to the development of efficient methods to directly determine estimates of the collapse load of a given structural model without resorting to iterative or incremental analysis. For t ...
of structural members subjected to bending, it is assumed that an abrupt transition from elastic to ideally plastic behaviour occurs at a certain value of moment, known as
plastic moment
In structural engineering, the plastic moment (Mp) is a property of a structural section. It is defined as the moment at which the entire cross section has reached its yield stress. This is theoretically the maximum bending moment that the section ...
(M
p). Member behaviour between M
yp and M
p is considered to be elastic. When M
p is reached, a plastic hinge is formed in the member. In contrast to a
friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction:
*Dry friction is a force that opposes the relative lateral motion of t ...
less hinge permitting free rotation, it is postulated that the plastic hinge allows large rotations to occur at constant plastic moment M
p.
Plastic hinges extend along short lengths of beams. Actual values of these lengths depend on cross-sections and load distributions. But detailed analyses have shown that it is sufficiently accurate to consider beams rigid-plastic, with plasticity confined to plastic hinges at points. While this assumption is sufficient for
limit state analysis, finite element formulations are available to account for the spread of plasticity along plastic hinge lengths.
[{{cite journal , doi = 10.1061/(ASCE)0733-9445(2006)132:2(244) , volume=132 , title=Plastic Hinge Integration Methods for Force-Based Beam–Column Elements , year=2006 , journal=Journal of Structural Engineering , pages=244–252 , last1 = Scott , first1 = Michael H. , last2 = Fenves , first2 = Gregory L., issue=2 ]
By inserting a plastic hinge at a plastic limit load into a statically determinate beam, a kinematic mechanism permitting an unbounded displacement of the system can be formed. It is known as the collapse mechanism. For each degree of static indeterminacy of the beam, an additional plastic hinge must be added to form a collapse mechanism
Sufficient number of plastic hinges(N) required to make a collapse mechanism (unstable structure):
N=Degree of static indeterminacy + 1
References
Building engineering
Structural engineering