Title of the project

The aim of the research project is to derive the design value of the post-cracking tensile strength for steel fiber-reinforced ultra-high performance concrete (UHPFRC). By taking into account the size dependence of the scattering, sufficient reliability is to be guaranteed and at the same time the economic efficiency of the construction method is not to be jeopardized.

Compared to the (normal-strength) steel fiber reinforced concrete covered by the DAfStb guideline "Steel fiber reinforced concrete", the steel fiber content of steel fiber reinforced UHPFRC is significantly higher. Accordingly, the calculated contribution of the steel fibers to the overall load-bearing capacity is considerable, so that no further reinforcement (e.g. in the form of shear force reinforcement, splitting tensile reinforcement, etc.) is required in addition to (prestressing bed) prestressing, even for components subject to bending loads. This allows a significantly reduced massiveness of the construction, a high degree of prefabrication, an increased service life and high resource efficiency. However, the implementation of new forms of construction and execution in building practice presupposes that the calculated performance of the cost-intensive steel fibers can actually be used. In this respect, in addition to reliability, the possibility of material-compatible design and the question of the cost-effectiveness of the construction method are closely linked to the question of defining an appropriate design value for post-cracking tensile strength.

A particular difficulty in defining a safety concept for steel fiber reinforced concretes is generally that the scatter of the post-cracking tensile strength depends essentially on the size of the drawn cross-sectional area: If small cross-sections are considered, such as those used in building material testing, there is a high probability that the number of fibers in a section will assume a very large or very small value, and this results in very high coefficients of variation for the post-cracking tensile strength compared to other strength parameters. As the cross-sectional area increases, it becomes increasingly unlikely that the number of fibers will assume an extreme value.

Based on these fundamental considerations, specific investigations are to be carried out as part of the research project in order to quantify the effects described. The data will then be used to derive a design value for the post-cracking tensile strength of steel fiber-reinforced UHPFRC. In principle, the concept should be based on the DAfStb guideline "Steel fiber reinforced concrete" and take into account the influence of size on the scattering.

Publications

LEUTBECHER, T.; HECK, L., 2026. Safety concept for ultra-high-performance fiber-reinforced concrete subjected to tension | Safety concept for tensile-stressed steel fiber-reinforced ultra-high performance concrete. In: Congress documents 70th BetonTage: Markets for people. Ulm, March 10-12, 2026. Betonwerk und Fertigteil-Technik/Concrete Plant and Precast Technology. 92(3), 70. ISSN 0373-4331