01-13-2011, 07:09 PM
plastic hinge
As a column experiences earthquake-induced lateral displacements
while supporting gravity loads, severe damage is observed in
regions subjected to large moments. These regions are commonly
referred to as plastic hinges and they experience large inelastic
curvatures. The inelastic curvatures in plastic hinges are typically
assumed to be constant over the plastic hinge length, lp, to simplify
the estimation of the tip displacement of a column. Therefore, if the
plastic hinge length is known, the tip displacement of a column can
easily be obtained by integrating curvatures, and vice versa. As
part of the research reported in this paper, the effects of axial load
and shear span-depth ratio (L/ h) on lp are evaluated experimentally.
Based on the experimental observations, a new analytical
approach that can be used to estimate lp is presented. Finally, the
research findings are synthesized into a simple expression that can
be used to estimate lp
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plastic hinges detailing
In recent revisions of the structural design codes in New Zealand,
a number of changes have been made to seismic design provisions.
One of the more significant revisions was the way in which the level
of detailing is determined for potential plastic hinges. Previously, the
level of detailing was based principally on the structural ductility
factor, which is broadly similar to the reduction factor R used in
U.S. practice. With the revision, the level of detailing is based on the
predicted magnitude of curvature that a plastic hinge is required to
sustain in the ultimate limit state. This paper explains why the
structural ductility factor does not give a reliable guide to the
deformation sustained in an individual plastic hinge. In addition,
based on test results of 37 beams, 25 columns, and 36 walls, design
curvature limits are proposed for different categories of plastic hinge.
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