![]() |
Computational & Technology Resources
an online resource for computational,
engineering & technology publications |
Civil-Comp Proceedings
ISSN 1759-3433 CCP: 75
PROCEEDINGS OF THE SIXTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: B.H.V. Topping and Z. Bittnar
Paper 10
An Optimal Plastic Shakedown Design F. Giambanco, L. Palizzolo and A. Caffarelli
Dipartimento di Ingegneria Strutturale e Geotecnica, Università degli Studi di Palermo, Italia Full Bibliographic Reference for this paper
F. Giambanco, L. Palizzolo, A. Caffarelli, "An Optimal Plastic Shakedown Design", in B.H.V. Topping, Z. Bittnar, (Editors), "Proceedings of the Sixth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 10, 2002. doi:10.4203/ccp.75.10
Keywords: finite element structures, elastic plastic behaviour, optimal design, elastic shakedown, plastic shakedown, ratchet.
Summary
It is known that an elastic plastic structure subjected to a combination of cyclic
and steady loads exhibits, after a transient phase, a steady-state response
independent of the initial conditions and having the same periodicity features as the
cyclic loads [1]. The steady-state structural response can be characterized by: an elastic
shakedown behaviour, with plastic strain rates vanishing identically; or a plastic
shakedown behaviour, with plastic strain rates non vanishing, but the plastic strain
field resulting in the cycle is nought; or, finally, a ratchetting behaviour with non
vanishing plastic strain field resulting in the cycle.
In the space of the load parameters
The optimal design of structures constituted by finite elements with elastic plastic constitutive behaviour, subjected to loads as above described, has been studied taking into account different resistance criteria [2,3,4]. Multicriteria optimal design formulations [5] have been also proposed taking contemporaneously into account different resistance criteria and assuming for each criterion a suitably chosen safety factor. The structures obtained effecting the optimal designs above described exhibit the required behaviour under the prescribed conditions. In particular, the structure obtained by means of the multicriteria optimal design possesses the required safety factor with respect to instantaneous collapse and, at the same time, guarantees a good behaviour in serviceability conditions. Unfortunately, unless further suitable conditions be imposed, also structures so well designed may be exposed to incremental collapse, instead to alternating plasticity, when for a given fixed load the cyclic loads are even slightly above the elastic shakedown limit. As a consequence, in such condition, although the instantaneous collapse is prevented, the structure may be addressed to lose its functionality and/or to collapse in a few cycles.
Aim of the present paper is to propose a formulation of the optimal plastic
shakedown design of finite element elastic plastic structures subjected to a
combination of steady and cyclic loads, such that ratchet strain be prevented. It is
based on a known property of bodies in plastic shakedown
conditions [6,7].
Actually, in such a condition, the body can be subdivided into two portions: the first
one An application concludes the paper. References
purchase the full-text of this paper (price £20)
go to the previous paper |
|