A Strain-Based Constitutive Model for Concrete under Tension in Nonlinear Finite Element Analysis of RC Flexural Members

In this paper, a two-phase strain-based constitutive model is proposed for concrete under tension. First phase deals with modelling uncracked concrete while the behaviour of concrete in cracked condition is modelled in second phase with appropriate theoretical support. A bilinear tension softening curve of concrete defined in crack width-stress space is taken as the basis to propose the model. Smeared representation of reinforcement and cracks along with multi-layered geometry definition of reinforced concrete (RC) structures is used to implement the model. Through this, it is shown that change in the orientation of tensile cracks with increasing load on the structure can be accounted. Stress transfer between cracked concrete and reinforcing bar is made use of to model the slip between them. By applying energy equivalence principle, simple expressions are derived for crack width as function of strain and fracture energy of concrete. For validation of the model and other associated features, two sample RC structures are analysed for their nonlinear response up to ultimate state. Computed responses are found to match closely with those obtained in experiments conducted by the authors and others. Through this, superior performance of the proposed model to evaluate the nonlinear response of RC flexural members is demonstrated.