3D meso-scale investigation of ultra high performance fibre reinforced concrete (UHPFRC) using cohesive crack model and Weibull random field

Abstract

Ultra high performance fibre reinforced concrete (UHPFRC) is composed of fibres, mortar, fibre-mortar interfaces, and pores randomly distributed in space, and thus has heterogeneous mechanical properties and complicated failure mechanisms at micro/meso-scales. This study aims to develop a highly effective 3D finite element modelling approach to simulate both the mortar heterogeneity and the complicated failure mechanisms in UHPFRC materials and structural members. In this approach, Weibull random fields are used to characterize random properties (such as moduli, strength and fracture energy) of the mortar caused by defects such as pores and microcracks; pre-inserted cohesive interface elements with softening constitutive laws are applied to model multi-cracking behaviour; specific probability density distributions are adopted to describe the random orientation of fibres in the mortar, and orientation-dependent bond-slip relations are developed to model fibre-mortar interactions. The fibres are rigidly embedded in the mortar so that non-conforming finite element meshes can be used conveniently. The modelling approach has been validated by extensive simulations of single fibre pull-out tests and direct tensile tests of UHPFRC specimens with thousands of fibres in agreement with experimental data. It is found that the modelling approach is highly efficient in capturing the fibre crack-bridging effect, simulating the damage and fracture initiation and evolution, and quantifying the load-carrying capacities with statistical analyses considering fibre orientation and mortar heterogeneity.