Elasto-plastic and damage modeling of reinforced concrete

Modeling the mechanical behavior of Reinforced Concrete (RC) is still one of the most difficult challenges in the field of structural engineering. The Nonlinear Finite Element Analysis (NFEA) and modeling of the behavior of RC members are the primary goals of this study. The macroscopic components of RC, Concrete material and reinforcing steel, are represented herein by separate material models. These material models are combined together using a model that describes the global effect of interaction between reinforcing steel and concrete in order to simulate the behavior of the composite RC material. A thermodynamically consistent constitutive model for concrete that incorporates concrete-plasticity and fracture-energy-based continuum damage mechanics is presented. An effective stress space plasticity yield criterion, with multiple hardening functions and a non-associative plasticity flow rule, is used simultaneously with two (tensile and compressive) isotropic damage criteria. The spectral decomposition of the stress tensor into tensile and compressive components is utilized in all criteria in order to simulate different responses of the material under various loading patterns. The damage criteria are based on the hydrostatic-deviatoric sensitive damage energy release rates in tension and compression derived from the Helmholtz free energy function. Three dissipation mechanisms are defined, one for plasticity and two for damage, to control the dissipation process of the material model. Elastic-plastic models that account for isotropic perfectly-plastic and plastic-strain-hardening (linear, bilinear and nonlinear) of the steel reinforcement are provided as well. The global effect of bond-slip is incorporated into the stress-strain diagram of the reinforcing bars in an attempt to describe this interaction phenomenon in a stress-strain driven environment. The Numerical implementation and application are important parts of this study. A suitable elastoplasticity-implicit/damage-explicit scheme is adapted here for the integration of the incremental constitutive equations. The elastic-predictor, plastic-corrector and damage-corrector steps are used to facilitate the integration procedure. The constitutive approach is implemented, through numerical algorithms; in the advanced FE software ABAQUS via user defined material subroutine UMAT to analyze and better describe the overall behavior of such a composite material. Concrete and RC beams subjected to static-short-term-monotonic loading are analyzed in an assumed isothermal environment. The simulated results are compared to experimental studies conducted by other researchers