Lumped Plasticity Model Research Articles

Simplified Model of Unilateral Damage for RC Frames

This paper presents an approach based on the concepts of continuum damage mechanics and standard inelastic analysis of reinforced concrete (RC) frames, modeling the hysteretic behavior of RC frames. A frame member is considered as the assemblage of an elastic beam-column and two inelastic hinges, as in the traditional lumped plasticity models. Three sets of internal variables are introduced that measure plastic rotations and state of damage of the member. Proposed as functions of the internal variables are an expression for the flexibility matrices and the complementary strain energy of a member. A resulting unilateral model is verified in simulations of various experiments for which data were available in the literature. The model is very simple and consequently not comprehensive; however, the technique is amenable to further generalizations.

Calcul simplifié de portiques endommageables

ABSTRACT A finite element formulation for inelastic frames is proposed. This formulation takes into account elasto-plastic effects and damage. The element is based upon the lumped plasticity model where inelastic effects are assumed to be lumped at some inelastic hinges. Therefore hinge's damage parameters and the notion of “damaged hinge” are introduced. In this framework unilateral behavior, large displacements and inelastics effects are taken into account. Internal variable evolution laws are identified for the particular case of reinforced concrete frames. Numerical implementation in standard finite element codes is described. Some numerical examples are shown.

Nonlinear analysis of lattice structures

The paper describes a nonlinear analytical technique developed by the authors in recent years for predicting the structural response of large scale lattice structures. This type of structure is generally more sensitive to imperfections; hence, the analysis method needs to consider the various nonlinear effects. Sources of nonlinearity affecting the ultimate behaviour of lattice structures include geometric nonlinearity, material nonlinearity, joint flexibility and slippage. Geometric nonlinearity can be accounted for by incorporating the effect of initial stress as well as geometrical variations in the structure during the loading process. For large scale lattice structures, the material nonlinearity can be incorporated by using the lumped plasticity model, while the effect of joint flexibility can be incorporated by modifying the tangent stiffness of the element using an appropriate moment—rotation relation for the joint. The nonlinear formulation has been applied to a number of example problems selected to demonstrate the applicability and versatility of the method.

Elasto‐Plastic Finite Element Models for Angle Steel Frames

The paper compares two elasto-plastic models for incorporating the effects of material nonlinearity into a finite element procedure in the large deflection analyses of angle beam columns and trusses. These are the fiber and the lumped plasticity models. In the fiber model, the element cross section is divided into a finite number of elementary areas, from which the sectional rigidities, resisting forces, and moments, allowing for material yielding and strain-unloading, are calculated. In the lumped plasticity model', the inelastic behavior is defined for the whole cross section. The stress resultants in the cross section interact to produce yielding for the section. Yielding in the element is treated in a lumped manner, in which the plasticity effects are assumed to occur only at generalized locations (plastic hinges), while the element between the hinges remains elastic. Numerical studies of the large deflection behavior of restrained imperfect angle columns, K-braced angle frames, and of single-angle web member trusses using the two elasto-plastic models are presented. Tests on two pairs of angle trusses with web members on either the same side or opposite sides of the chord are described.

Lumped Damage Models For OligocyclicFatigue In RC Frames

This paper presents a simplified damage theory for the nonlinear analysis of frames based on the lumped plasticity models and continuum damage mechanics. Based on this formulation, a particular model for RC frames under oligocyclic fatigue is proposed.