# Non-Destructive Multi-Method Assessment of Steel Fiber Orientation in Concrete +
Footnote †: This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ([[https://creativecommons.org/licenses/py/4.0/](https://creativecommons.org/licenses/py/4.0/)]([https://creativecommons.org/licenses/py/4.0/](https://creativecommons.org/licenses/py/4.0/))). [PERSON]  
1 Bundesanstalt fur Materialforschung und -prufung (BAM), 12205 Berlin, Germany; [EMAIL_ADDRESS]  
(F.M. ); [EMAIL_ADDRESS]  
[PERSON]  
1 Bundesanstalt fur Materialforschung und -prufung (BAM), 12205 Berlin, Germany; [EMAIL_ADDRESS]  
(F.M. ); [EMAIL_ADDRESS]  
(D.M.) [PERSON]  
1 Bundesanstalt fur Materialforschung und -prufung (BAM), 12205 Berlin, Germany; [EMAIL_ADDRESS]  
[PERSON]  
1 Bundesanstalt fur Materialforschung und -prufung (BAM), 12205 Berlin, Germany; [EMAIL_ADDRESS]  
(F.M. ); [EMAIL_ADDRESS]  
(D.M.) [PERSON]  
1 Bundesanstalt fur Materialforschung und -prufung (BAM), 12205 Berlin, Germany; [EMAIL_ADDRESS]  
(F.M. ); [EMAIL_ADDRESS]  
(D.M.) Footnote 1: [[https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci)]([https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci))  
Footnote 2: [[https://www.mdpi.com/journals/pdf/1](https://www.mdpi.com/journals/pdf/1)]([https://www.mdpi.com/journals/pdf/1](https://www.mdpi.com/journals/pdf/1))  
the emerging guidelines and standards, e.g., in the fib Model Code 2010 and 2020 [2; 3], the German standard DIN 1045 and the associated DafStb-Richtlinie Stahlfaserbeton [4], the ACI 544.4 Guide to Design with Fiber-Reinforced Concrete [5] and, most importantly, in the inclusion of provisions for the design with SFRC in the next generation of Eurocode 2 [6]. The design with SFRC strongly depends on the properties of the fiber reinforcement, such as the dosage of the fibers (typically expressed in weight of fibers per total volume of concrete), the material (steel, natural, synthetic), the dimensions (length and cross-section) and the shape of the fibers (straight, crimped, hooked, etc.) Furthermore, modern design concepts strongly rely on consistent and predictable overall distribution and orientation characteristics for fibers in the hardened concrete mix, since the amount and inclination of the fibers relative to the internal stress directions of the structural component have been shown to significantly influence its load-bearing performance [7]. Alignment of fibers in a parallel direction to the prevailing tensile stresses understandably increases the composite matrix's resistance in tensile rupture, and unfavorable fiber distributions and orientations can even hinder the structural performance of concrete by inducing anisotropy and weak regions in the material. Fiber reinforcement in concrete aims to mainly arrest the concrete crack formation and propagation, which generally results in an increased tensile strength, ductility, and durability of the material. As seen in Figure 1, this effect is strongly dependent on the location of the fibers within the concrete matrix with respect to the cracking, which in turn forms in a nearly perpendicular direction to the tensile stresses in the material. These stresses are in turn bridged through the fibers intersecting the crack. Obviously, this behavior is strongly influenced by the orientation of fibers in relation to the principal tensile stresses (represented by the black arrows) and the resulting cracking planes. The fibers can, for example, have an orientation parallel to the cracking plane (blue), they can have a random orientation distribution in relation to the stress and crack planes (yellow), or be aligned parallel to the tensile forces and perpendicularly to the crack plane (red).