Performance-Based Fibre Design for Ultra-High Performance Concrete (UHPC)

Abstract

The paper presents a method to establish a performance-based fibre design of high-strength micro steel fibres for ultra-high-performance concrete (UHPC). The performance-based fibre design considers effects of fibre layout, fibre orientation, and type of loading (quasi-static and cyclic) and expands the current approach using experiences and suitability testing results. The performance-based fibre design is based on a so-called utilization rate, which is determined via pullout tests of high-strength micro steel fibres in UHPC under quasi-static as well as high cyclic loading with varying orientations and embedment depths. The utilization rate for a straight fibre pullout is 0.27 on average considering the measured tensile strength of the fibre and 0.50 considering the manufacturers specifications. For inclined fibres, additional bending stresses occur at the exit point of the fibre channels, leading to a significant increase in local tensile stress. Therefore, the utilization rate of inclined fibres under quasi-static loading is approximately 60–70% higher than in the case of straight embedded fibres (comparing it to the measured tensile strength). Comparing the utilization rate to the manufacturer’s specification, it increases to approximately 1.00. Under cyclic loading, the additional bending stresses in inclined fibres result in a local increase of the load amplitude, leading to a reduced fatigue resistance and premature fibre rupture, underlining the feasibility of a performance-based fibre design.

Cyclic Deterioration of High‐performance Concrete – Findings of the Priority Programme SPP 2020

“…Therefore, ultra-high-performance fibre-reinforced concrete (UHPFRC) usually requires high-strength micro steel fibres. Monotonic pull-out tests and calculations in [26] on the reference ultra-high-strength concrete with fibres showed that the fibre stresses were always smaller than the tensile strength of the fibre material. However, the results also show that fibre rupture occurs under cyclic loading.…”

“…The demonstrators used are notched beams with a span of 3.0 m, a height of 30 cm and a width of 15 cm. The concrete mixture and fibre type remained the same as in [26]. Figure 10 shows the evolution of the CMOD (crack mouth opening displacement) depending on the load cycles.…”

“…Since the results in [26] were based on small-scale samples, and it was not clear whether the fibre rupture also occurs on real scale components, a test programme has been set up for so-called UHPFRC demonstrators that represent component alike specimens. The demonstrators used are notched beams with a span of 3.0 m, a height of 30 cm and a width of 15 cm.…”