Influence of Test Configuration on the Bond–Slip Behavior of Hooked-End Steel Fibers in Concrete: Quantity, Inclination, and Spacing
Abstract
1. Introduction
2. Materials and Methods
2.1. Material Properties
2.2. Composition and Preparation of the Mortar
2.3. Casting of the Pullout Specimens
2.4. Testing of the Pullout Specimens
2.5. Statistical Analysis
3. Experimental Results
3.1. Influence of Fiber Inclination
3.2. Influence of Fiber Spacing and Number of Fibers
4. Numerical Analysis
4.1. Three-Point Bending Test Simulations Setups
4.2. Mesoscale Simulation Analysis
5. Discussion
6. Conclusions
- The pullout loads for parameters PL1 and PL2 exhibited a clear and direct increase with fiber inclination, whereas the changes observed for PL3 were not statistically significant with varying fiber angles. This suggests that the influence of fiber inclination becomes less pronounced at higher stages of pullout, where kinetic friction predominates. At 30° inclination, approximately 21% of the test specimens experienced fiber rupture before the completion of pullout, suggesting that the stress generated during pullout exceeded the tensile strength of the fibers for higher inclinations.
- For setups with varying fiber numbers and spacings (F2S7, F2S14, F4S7, F4S14), no significant differences were observed in pullout loads for PL1, PL2, and PL3 compared to the single-fiber setup (F1S0), indicating that fiber count does not notably affect pullout behavior. However, higher fiber counts reduced the interquartile range (IQR), suggesting less variability. The F4S7 setup, with closer fiber spacing, showed higher pullout loads for PL1 and PL2 than F4S14 (p < 0.05), implying that closely spaced fibers may enhance load transfer by reinforcing the surrounding matrix during the pullout process.
- The pullout test results were used to calibrate a multiscale numerical model simulating fiber–matrix interactions in three-point bending tests (3-PBTs). The model effectively captured the anchorage effects of hooked-end fibers, with simulation results generally matching experimental data. The post-cracking load response was influenced by bond–slip law parameters from pullout tests. While the overall load–displacement behavior was consistent, discrepancies in the fR1 parameter highlighted the need for model refinement, particularly in capturing fiber slippage early in cracking. In terms of the fR3 parameter, the numerical results seemed consistent with the average experimental curves.
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Materials | d10 | d50 | d90 | FM |
---|---|---|---|---|
Cement CEM I 52.5R | 0.15 | 0.27 | 0.58 | − |
Siliceous river sand | 0.07 | 0.80 | 3.70 | 1.39 |
Artificial granite sand | 0.95 | 13.40 | 35.00 | 2.76 |
Characteristic | d10 |
---|---|
Length (mm) | 60 |
Diameter (mm) | 0.75 |
Aspect ratio (l/d) | 80 |
Specific weight (kg/m3) | 7850 |
Tensile strength (MPa) | 1225 |
Young’s modulus (GPa) | 210 |
Materials | Dosage (kg/m3) |
---|---|
Cement CEM I 52.5R | 751 |
Water | 289 |
Siliceous river sand | 705 |
Artificial granite sand | 471 |
Superplasticizer | 5.25 |
Identification | Number of Fibers | Spacing (mm) | Inclination (in °) |
---|---|---|---|
F1S0 I0 | 1 | N.A. * | 0 |
F1S0 I15 | 1 | N.A. * | 15 |
F1S0 I30 | 1 | N.A. * | 30 |
F2S7 | 2 | 7 | 0 |
F2S14 | 2 | 14 | 0 |
F4S7 | 4 | 7 | 0 |
F4S14 | 4 | 14 | 0 |
Number of Load Steps | Truss Elements (Fibers) | 3-Noded Triangular Elements (Concrete) | 4-Noded Triangular Elements (CFEs) | Fibers Crossing the Fracture Section |
---|---|---|---|---|
10,000 | 2565 | 4745 | 3074 | 168 |
Compressive Strength (MPa) | Tensile Strength (MPa) | Young’s Modulus (GPa) | Poisson’s Ratio (-) | Fracture Energy (N/mm) | Compressive Parameters |
---|---|---|---|---|---|
46.50 | 2.39 | 29.25 | 0.20 | 0.146 | A = 1.00 B = 0.89 |
Parameters | Central Region | FI10 | F2S7 | F2S14 | F4S7 | F4S17 |
---|---|---|---|---|---|---|
τmax (MPa) | 0.53 | 19.47 | 19.74 | 18.93 | 20.51 | 18.57 |
τf (MPa) | 0.34 | 5.34 | 4.89 | 5.12 | 5.20 | 4.88 |
s1 (mm) | 0.18 | 0.57 | 0.64 | 0.64 | 0.92 | 0.82 |
s2 (mm) | 1.29 | 5.27 | 5.24 | 5.24 | 5.42 | 5.32 |
Fiber Content (kg/m3) | Cx | Cy | Cz |
---|---|---|---|
41.44 ± 3.27 | 0.515 ± 0.010 | 0.286 ± 0.008 | 0.199 ± 0.003 |
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Maia, J.S.; Serafini, R.; Mineiro, M.L.R.; Batista, A.M.; Agra, R.R. Influence of Test Configuration on the Bond–Slip Behavior of Hooked-End Steel Fibers in Concrete: Quantity, Inclination, and Spacing. Buildings 2025, 15, 868. https://doi.org/10.3390/buildings15060868
Maia JS, Serafini R, Mineiro MLR, Batista AM, Agra RR. Influence of Test Configuration on the Bond–Slip Behavior of Hooked-End Steel Fibers in Concrete: Quantity, Inclination, and Spacing. Buildings. 2025; 15(6):868. https://doi.org/10.3390/buildings15060868
Chicago/Turabian StyleMaia, Jonatas Santana, Ramoel Serafini, Maria Luísa Ribeiro Mineiro, Alicia Martinez Batista, and Ronney Rodrigues Agra. 2025. "Influence of Test Configuration on the Bond–Slip Behavior of Hooked-End Steel Fibers in Concrete: Quantity, Inclination, and Spacing" Buildings 15, no. 6: 868. https://doi.org/10.3390/buildings15060868
APA StyleMaia, J. S., Serafini, R., Mineiro, M. L. R., Batista, A. M., & Agra, R. R. (2025). Influence of Test Configuration on the Bond–Slip Behavior of Hooked-End Steel Fibers in Concrete: Quantity, Inclination, and Spacing. Buildings, 15(6), 868. https://doi.org/10.3390/buildings15060868