Journal of Engineering Mechanics ASCE, 123 (1997), 8-14.
ANALYTICAL AND NUMERICAL SOLUTIONS
FOR FRAMES WITH SOFTENING HINGES
Swiss Federal Institute of Technology
The paper describes beam elements with inelastic
hinges capable of modeling softening due to damage
in building frames under severe loadings. A condition for uniqueness
on the element level is derived, and the behavior of the model
is compared to analytical solutions of simple
structures (a single column and a portal frame).
An application to post-peak analysis of a multi-bay frame
is presented. Depending on the beam-to-column stiffness ratio
and on a certain ductility parameter, various
failure modes can occur, ranging from distributed to highly localized
ones. This leads to a special type of size effect
on the peak load, which is assessed numerically and related to
analytically derived solutions valid in extreme situations - the elastic
limit and the plastic limit.
Summary and Conclusions
Beam elements with embedded softening hinges have been developed.
If the element length is smaller than a certain critical value,
the response of the element can be uniquely determined
from the rate of end rotations with respect to the beam chord.
The developed elements exactly reproduce analytical solutions of
several typical examples.
An application to analysis of a multi-bay frame
has been demonstrated. Depending on the value of a certain ductility
parameter, the failure patterns range from distributed modes to highly
localized ones. This results into a dependence of the
nominal peak load (per column) on the number of columns, which can be
considered as a special type of size effect.
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13 December 1996 /