Julio Flórez-López

A simplified damage mechanics approach to nonlinear analysis of frames

Abstract This paper presents a general formulation for frame analysis based on ‘lumped dissipation models’ and continuum damage mechanics. A particular model for RC frames based on this framework is proposed and the numerical implementation of simplified damage models in commercial finite element programs is described.

Three-dimensional analysis of reinforced concrete frames based on lumped damage mechanics

This paper presents a general formulation for the analysis of reinforced concrete frames. The model has been developed within the framework of lumped damage mechanics. This is a theory based on the methods of continuum damage mechanics, fracture mechanics and the concept of plastic hinge. The paper also describes the numerical implementation of the model in the finite element programs. The model is evaluated by the numerical simulation of three tests reported in the literature. Two of them deal with a column subjected to variable axial loads and biaxial flexure. The third is a two-story three-dimensional frame subjected to earthquake loadings outside the principal directions of the frame.

MODEL OF DAMAGE FOR RC ELEMENTS SUBJECTED TO BIAXIAL BENDING

This paper describes the modeling of the biaxial bending of RC frames within a new framework called lumped damage mechanics (LDM). In this alternative approach, the models are based on the methods of fracture mechanics and the concept of plastic hinge. LDM can be considered as a branch of fracture mechanics for framed structures. LDM integrates concepts such as plastic hinge, damage variable, energy release rate, deformation equivalence hypothesis and RC standard theory. In order to validate the model, some numerical simulations of tests reported in the literature are presented. A good agreement between tests and model can be observed.

Frame analysis and continuum damage mechanics

In this paper a unified formulation for damage analysis of steel and reinforced concrete frame members is presented. This formulation is based on the methods of continuum damage mechanics and on the notion of inelastic hinges. Particular models for frames under monotonic, low cycle and cyclic loading are described.

A boundary element formulation for a class of non-local damage models

This paper proposes and discusses a boundary element formulation for a particular class of non-local damage models. The formulation as well as the boundary element computational code developed during this research have proven to be very simple and efficient, providing reliable information on the strains and stresses in damage-softening models. The numerical approach uses a finite-grid to estimate the damage values. Some illustrative numerical examples, which show the simplicity and versatility of the proposed approach, are included and discussed in detail.

Model of damage for steel frame members

The main purpose of this paper is to propose a model of damage for steel frame members based on the methods of continuum damage mechanics and the concept of the plastic hinge. It first describes a particular model of continuum damage for metals, the Lemaitres model. It is then shown, on the basis of experimental results, that this model could be used in the analysis of steel frames if it is combined with a multilayered procedure. In the last part of the paper, a new model for a frame member with damaged-plastic hinges is proposed. In this model, a set of internal variables that measure the state of damage of the hinges is introduced. These variables and the conventional plastic deformations define the behavior of the hinges. It is shown that the uniaxial behavior of the material and the behavior of the hinges under flexural effects have the same general form. A yield function for a damaged-plastic hinge with kinematic hardening and a damage evolution law are then proposed.

Simulation of damage in RC frames with variable axial forces

The purpose of this paper is to describe how the methods and concepts of continuum damage and fracture mechanics can be applied to the modelling of the hysteretic behaviour of Reinforced Concrete (RC) frame members under variable axial loads. A frame member is considered as the assemblage of an elastic beam-column and two inelastic hinges, as in conventional nonlinear analysis of RC frames. As a result of the combination of damage mechanics and standard RC theory, a simplified model of damage is proposed and implemented as a finite element (FE). This new element can be used with any non-linear commercial FE program. The numerical simulation of several experiments, for which data were available in the literature, verifies the accuracy of the model. Copyright

A two-field finite element formulation for elasticity coupled to damage

A two-field variational formulation is proposed for continuum damage mechanics problems. This formulation is applied to the numerical solution, via the finite element method, of initial boundary value problems arising in elasticity coupled to damage; the nodal variables are the displacement and damage fields. Simple examples are presented to demonstrate the advantages and limitations of this formulation.

Modeling of local buckling in tubular steel frames subjected to cyclic loading

Abstract In this paper, a model of the behavior of metallic structures subjected to flexural effects is proposed. The model focuses on the description of failure due to local buckling. It is assumed that the main inelastic phenomena involved in the process: plasticity and local buckling, can be lumped at inelastic hinges. The model takes into account that in planar frames, two local buckling can appear in the plastic hinge region: one due to a positive moment the other one related to a negative moment. The elastic behavior of frame members with two local buckling is assumed as unilateral. The plastic behavior is described using the concept of equivalent moment on a damaged plastic hinge. A new hypothesis, that authors have called “counter-buckling”, is introduced. The counter-buckling concept states that as a consequence of the evolution of one local buckling, the other one results partially blocked. The notion of counter-buckling is used to describe local buckling evolution during cyclic loadings. Finally, the model is verified through the numerical simulation of several experimental tests on frame members and framed structures.

Portal of damage: a web-based finite element program for the analysis of framed structures subjected to overloads

This paper describes a web-based finite element program called portal of damage. The purpose of the program is the numerical simulation of reinforced concrete framed structures, typically buildings, under earthquakes or others exceptional overloads. The program has so far only one finite element based on lumped damage mechanics. This is a theory that combines fracture mechanics, damage mechanics and the concept of plastic hinge. In the case of reinforced concrete frames, the main mechanism of deterioration is cracking of concrete. Cracking in a frame element is lumped at the plastic hinges. Cracking evolution in the plastic hinge is assumed to follow a generalized form of the Griffith criterion. The behavior of a plastic hinge with damage is described via the effective stress hypothesis, as used in continuum damage mechanics. The portal that can be accessed using any commercial browser (explorer, netscape, etc.) allows to: (a) Create an account in a server.(b) Make use of a semi-graphic pre-processor to create an input file with a digitalized version of the structure.(c) Run a dynamic finite element program and monitor the state of the process.(d) Download or upload input and output files in text format.(e) Make use of a graphic post-processor.