Journal of Engineering Mechanics ASCE, 123 (1997), 8-14.

ANALYTICAL AND NUMERICAL SOLUTIONS
FOR FRAMES WITH SOFTENING HINGES

Milan Jirásek
Swiss Federal Institute of Technology
LSC -DGC, EPFL, 1015 Lausanne, Switzerland

Abstract

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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EPFL / 13 December 1996 / Milan.Jirasek@epfl.ch