Pull-out mechanism of striated steel fibers in ultra-high performance concrete (UHPC): Experimental study and analytical modeling

Abstract

This study presents the first mechanistic investigation of striated steel fibers, a newly developed fiber type optimized for ultra-high performance concrete (UHPC). Through single-fiber pull-out experiments and finite element (FE) simulations, the research examines the interfacial mechanisms governing load transfer between striated fibers and UHPC. The striated fibers, featuring micrometer-scale surface depressions, exhibit a distinctive multistage pull-out response marked by alternating load rises and drops, which correspond to successive engagement and release of the striations. This behavior, not observed in conventional deformed or smooth fibers, reflects a unique combination of adhesion, frictional sliding, and mechanical interlocking within the dense UHPC matrix. On average, the striated fibers achieved 104% higher maximum pull-out load and 126% greater equivalent bond strength than smooth fibers, attributed to the formation of localized shear keys and enhanced frictional resistance. Detailed computational simulation captured the evolution of these anchorage-sliding cycles and clarified the local crushing and reanchoring of the matrix around each striation. An analytical model was also developed to represent both the frictional and anchorage contributions to pull-out resistance. The findings provide the first direct experimental and numerical evidence of the progressive bond mechanisms in striated fibers and establish a mechanistic foundation for optimizing their geometry and application in next-generation UHPC systems.