| Summary: | Ultra high performance fibre reinforced concrete is a relatively new material developed by taking advantage of advances in concrete technology and material science to enhance its microstructure. Short, discrete fibres with a high aspect ratio (50-100) substantially improve its ductility. The material's overall performance is therefore superior to other types of reinforced and fibre reinforced concretes with respect to strength, ductility and durability. However, despite its enormous potential, adoption of the material is still relatively low. This is attributed not only to its higher cost but also to a lack of enough experimental data and widely accepted design standards. While some effort is being made to develop numerical models for UHPFRC, many are based on multiscale frameworks requiring the measurement of microscale parameters. Such parameters are difficult to measure whereas for most practical purposes design normally requires material properties measured at the macroscale. The overall aim of this research therefore is to propose a numerical damage model for UHPFRC that uses material properties from standard tests and that can simulate the flexural behaviour of UHPFRC and predict its failure loads. Initial modelling enabled identification of suitable approaches for estimating the elastic modulus, tensile strength and fracture energy values appropriate for simulating the material's flexural behaviour. A comprehensive experimental investigation undertaken established the existence of size effect on the flexural stress at the end of linearity and flexural strength of notched and un-notched specimens with 2%, 4% and 6% fibre content. The tests also identified the significant effect of fibre content on the elastic modulus, tensile strength and fracture energy values. Therefore the effect of fibre content was incorporated into the proposed damage model by making these three material properties a function of it. This is done by incorporating values of estimated material properties into a bilinear traction separation law thereby also linking the damage to fibre content. The multiple fibre content effects represented include the spacing and number of fibres per unit cross-sectional area. The model adopts a smeared crack approach. It is implemented as a user defined material model in ABAQUS finite element software and written in FORTRAN code. The model's ability to simulate the load deflection response was validated using two case studies. The model's predictions match test data reasonably well for specimens of different sizes, test arrangement and fibre contents. Therefore a validated numerical material model incorporating fibre content is proposed as a simple, practical and economical tool for predicting the material's flexural behaviour thereby achieving the overall aim of the study. This is one of the main contributions of this study. Another contribution is the establishment of size effects on the flexural properties of UHPFRC at 2%, 4% and 6% fibre contents. Finally values of material properties at these fibre contents estimated from test data and comparisons between the different modelling approaches are a valuable resource for similar studies in future.
|
|---|
