A unified tensile constitutive model for mono/hybrid fibre-reinforced ultra-high-performance concrete (UHPC)

Providing a representative and reliable tensile constitutive model for ultra-high-performance concrete (UHPC) has been challenging in the past due to the absence of standardised test methods. In this paper, the authors have proposed a unified constitutive model calibrated to the most commonly used types of steel fibres within the practical range of fibre content. While the novel model serves as the core, a comprehensive experimental program and results are pivotal for validating the model's effectiveness. In pursuit of this, the recently approved AASHTO standard test method was employed to offer standardised and comprehensive experimental insights into the direct tensile behaviour of mono/hybrid fibre-reinforced UHPC. A set of predictive equations, derived either empirically or from simple mechanics, to predict the key parameters defining the mechanical constitutive law of UHPC material subjected to uniaxial tension are introduced based on experimental findings. The proposed predictive equations and constitutive model exhibited robust predictions of tensile behaviour, aligning well with both the test results and additional independently tested UHPC specimens.