The motivation for this study is a new material design for wave energy convertor floater hull, which requires exceptional performance in harsh marine environment under extreme weather conditions. Fibre reinforced concrete (FRC) utilises its highest performance after initial cracking, exhibiting strain-hardening when the cracks bridged by fibres redistribute the stresses over larger volume of concrete and thus increase the load bearing capacity of the specimen. The proper numerical description of cracks is of major importance to obtain physically meaningful results for high performance concrete (HPC) reinforced with alternative reinforcements like short fibres or textile reinforcement. Thus, the goal is to introduce the numerical tool in order to investigate the behaviour of FRC and FRHPC members. Since, such tool can be calibrated for a given type of fibres, then for any new concrete mixes, if only the properties of plain concrete are known, one can easily estimates the influence of steel fibres additive without necessity to proceed additional series of experiments. The main idea of presented approach is to assume the fully 3D modelling with taking into account explicitly the distribution and orientation of the steel-fibres embedded in 3D concrete continuum. Moreover, an explicit bond-slip interaction between each fibre and concrete is implemented. Consequently, different failure modes associated with fibres pull-out or fibres rupture can be independently simulated. As a benchmark, results obtained from experimental campaign on different specimens made from concrete with steel fibres of different sizes and dosages were taken. Results of numerical simulations were directly compared with experimental outcomes in order to validate and calibrate FE-model and to introduce the efficient numerical modelling tool.

A computationally-efficient multi-scale model is developed for the analysis of fiberreinforced concrete (FRC) structures. At the macro-scale, the structural behaviour under mechanical loading is analysed using the Finite Element Method, where in each integration point the effective constitutive response of the FRC is computed considering a representative collection of cohesive particles, fibers and air voids and applying a homogenization technique known as the Granular Micromechanics Approach. The micro-scale kinematic measures are calculated from the strain tensor in the material point by adopting the kinematic hypothesis. The micro-scale constitutive responses of the particle contacts and fibers are specified through path-dependent elasto-damage formulations. The constitutive laws of the particle contacts account for a strain-softening behavior for inter-granular tension and shear, and a strain-hardening behavior for inter-granular compression. The constitutive law for the fibers mimics the effect of elastic bonding between fiber and matrix, followed by fiber debonding and sliding under an increasing tensile load, eventually leading to complete pull-out. Under compression, the constitutive behaviour of fibers is determined by an initial, elastic branch, which continues into a failure branch that captures their combined buckling and crushing behaviour. The distribution of the fiber orientations is defined via a probability density function, and the homogenized Cauchy stress in a macro-scale material point is calculated by applying the Hill-Mandel microheterogeneity condition. The numerical solution procedure is strain-driven, where the macroscopic stress and tangential stiffness tensors are incrementally updated from the homogenized elasto-damage behavior of the particle contacts and fibers. The accuracy and efficiency of the multi-scale model are demonstrated by performing FEM simulations on the failure behavior of FRC samples subjected to uniaxial tensile load, and comparing the results to experimental data reported in the literature.