Abstract
The main objective of this report is to identify the current state of the art within design of steel fibre reinforced concrete (SFRC) in Europe. The report contains a short overview of the
theoretical background of SFRC in the form of a guideline survey, followed by practical examples demonstrating the design of a concrete structure with conventional bar
reinforcement, compared with partly and total fibre reinforcement of the various structure elements. The structural elements included in the practical examples are foundations, walls,
columns and slabs. Calculations due to deflections and cracking are omitted due to the present lack of calculation methods.
In the guideline survey, the following design guidelines are included;
- Norwegian preliminary guideline for steel fibre reinforced concrete (NPG for SFRC), Several contributors, Norway, 2006.
- Guidance for the Design of Steel-Fibre-Reinforced Concrete (GD of SFRC), Concrete Society, UK, 2007.
- Test and design methods for steel fibre reinforced concrete. σ-ε design method. Final Recommendation, RILEM TC 162-TDF, 2003.
According to both RILEM and GD of SFRC, the residual flexural strength of SFRC is to be determined experimentally. The NPG, on the other hand, opens for theoretical calculations to
determine the residual flexural strength. The preferable method for comparing the above mentioned guidelines would be to perform a design of a given ‘beam in bending’-situation
for each of the different guidelines, leading to accurate comparable results. This is however complicated due to the requirement for an experimentally determination of the residual
flexural strength in RILEM and GD of SFRC.
The design of the different structural elements in the practical examples shows that adding steel fibre to concrete has a favourable effect on the concrete's moment capacity. For
structural parts with a limited variation in moment and shear forces, fibre reinforcement is competitive. For e.g. flat slabs, with large moment and shear gradients, a relatively large
dosage of steel fibre is required to totally avoid conventional bar reinforcement. With respect to the shear capacity, adding steel fibre to the concrete has a very favourable effect. Hence, it can be propitious to use a combination of steel fibre reinforcement and bar reinforcement, where the steel fibres carry shear forces and parts of the moment. Consequently, adding 1 vol.-% steel fibre to concrete does have a significant effect on the concrete's capacity, and a combination of bars and fibres is the most realistic approach.
For a more thorough comparison of the guidelines in question, appurtenant prescribed bending test ought to be performed. With that, calculations for a given ‘beam in bending’-
situation can be performed for each of the different guidelines, leading to accurate comparable results. Incorporating design by additional guidelines for comparison should be
considered. In addition, design with more focus on SLS should be performed, i.e. where even effects due to deflections and cracking are considered.
An evaluation of steel fibre reinforcement versus conventional bar reinforcement with respect to building costs would be of big relevance due to future use of steel fibre
reinforcement.