Finite element modeling of confined concrete-I: Drucker–Prager type plasticity model

This paper first presents a critical review and assessment of the ability of the existing Drucker–Prager (D–P) type concrete plasticity models to predict the behavior of confined concrete using both experimental observations and numerical results. This assessment shows that for a D–P plasticity model to succeed in predicting the behavior of FRP-confined and other passively-confined concrete, it needs to be modified to possess the following three features: (a) a yield criterion including the third deviatoric stress invariant; (b) a hardening/softening rule which is dependent on the confining pressure; and (c) a flow rule which is dependent not only on the confining pressure but also on the rate of confinement increment. None of the existing D–P type models includes all three features, so they cannot be expected to lead to accurate predictions for both actively-confined and passively-confined (e.g. FRP-confined) concrete. A modified D–P type model, which includes all three features mentioned above, is then presented in this paper. The capability of the proposed model in providing close predictions of the behavior of both actively-confined and FRP-confined concrete is next demonstrated through comparisons between numerical predictions obtained using this modified D–P type model and available test results. Finally, the limitations of the proposed plasticity model are discussed. These limitations are addressed in the companion paper through the development of a plastic-damage model.