Time Dependent Deflection of FRC Members Under Sustained Axial and Flexural Loading

The inclusion of steel or polypropylene fibres into a concrete matrix can considerably improve the serviceability performance of reinforced concrete members. The benefits of including fibres in structural concrete have been extensively studied, and as a result, provisions for strength, and short-term serviceability conditions are contained in national codes of practice such as the Australian Standards for Concrete Structures and Concrete Bridges. Provisions relating to the long-term serviceability behaviour of fibre reinforced concrete (FRC) are either not included or can be seen to provide limited guidance to designers. This paper describes a method of analysis that can be applied to predict the time-dependent behaviour of cracked fibre (steel or macro-synthetic) reinforced concrete. The model is versatile and can handle a wide range of geometries, material properties and loading conditions. The layered modelling approach provides a high level of flexibility which allows for the consideration of variable creep, shrinkage and fibre properties, as a function of time. Results from the model have been compared to existing experimental data available in the literature and have been shown to correlate well. In addition, a sample analysis is presented to demonstrate the effects of residual tensile stress, tensile creep and variable shrinkage gradients on a FRC flexural section.