Constitutive modeling of steel-polypropylene hybrid fiber reinforced concrete using a non-associated plasticity and its numerical implementation

This paper presents a non-associated plasticity-based constitutive model for hybrid steel–polypropylene fiber reinforced concrete (HFRC) materials in an attempt to characterize the stress–strain responses under multiaxial loading scenarios. Together with a five-parameter loading surface and uncoupled hardening and softening regimes, a nonlinear plastic potential function is particularly introduced into the constitutive model with the material constants experimentally determined through a true triaxial compression test, which allows a more accurate estimation of the volumetric dilatency of HFRC. The influence of fiber parameters on the plastic flow direction is also addressed. Furthermore, the developed model is implemented into ABAQUS finite element package through a User-defined Material (UMAT) subroutine that can be applicable for the convenient use in numerical simulation of HFRC materials. A substepping scheme with error control for integrating the elasto-plastic stress–strain rate equations is presented in detail. Subsequently, the proposed model is evaluated by available multiaxial compression test results of both plain concrete and FRC reported by other researchers. It is shown that the constitutive model can realistically capture the stress–strain responses as well as the volumetric deformation of HFRC having various fiber reinforcement indices.