| The general formulation of a three-dimensional concrete model that can be used not only for nonlinear finite element analysis of three dimensional reinforced concrete structures but also for the steel confined and FRP (Fiber-Reinforced-Plastic) confined concrete structures under short term, non-proportional loads is presented in this study.; The hypoelastic model is based on the orthotropic approach and formulated in a strain driven constitutive driver. The model is based on the concept of equivalent uniaxial strains. The axes of orthotropy are assumed to be parallel to the principal stress axes; however, the principal strain axes are assumed not to be coaxial with the principal stress axes. The shear dilatant effects are included in the proposed model through the coupling between volumetric and deviatoric component of stress and strain. A uniaxial law for equivalent uniaxial strain and stress, namely the Popovics-Saentz curve, is implemented to better predict the elastic region with given initial stiffness and to control the post-peak behavior of concrete. To capture hydrostatic-like loading, a cap surface is derived and included in Willam and Warnke's failure surface. The model is strain-driven and can describe not only monotonic and cyclic loading, but also proportional and non-proportional loads. Post-Peak crushing in compression and cracking in tension are included. Furthermore, the model accounts for the transition between brittle-softening to ductile-hardening response in compression under increasing lateral confinement.; Correlation studies with available experimental tests such as uniaxial monotonic and cyclic load, biaxial monotonic load, and triaxial none-proportional cyclic load cases, are presented to demonstrate the model performance. The confinement effects caused by steel and FRP tubes are discussed and the concrete filled FRP tubes are analyzed by the proposed model. Finite element analysis of reinforced columns is performed to study the behavior of a rectangular reinforced concrete column using the proposed constitutive model. |
