Fatigue Behavior of Concrete Beams Prestressed with Partially Bonded CFRP Bars Subjected to Cyclic Loads
Abstract
:1. Introduction
2. Research Significance
2.1. Test Specimens and Jacking Setup
2.2. Test Program
3. Results and Discussions
3.1. F1FU/S1FU Specimens
3.2. F1PU/S1PU Specimens
3.3. F2PC/S2PC Specimens
3.4. Energy-Based Ductility Index
4. Results and discussions
- The F1FU specimen post-tensioned with a fully unbonded bar exhibited good fatigue performance and high ductility. No considerable reduction in beam stiffness or slippage in anchorage was observed during one million cycles. In a static test, conducted after completing one million cycles, the F1FU specimen, despite beam failure by non-prestressing reinforcement rupture, had the highest ductility index.
- It was observed that S1FU and F1FU specimens experienced failure by non-prestressed reinforcement during static tests. From a design point view, an adequate amount of non-prestressing reinforcement should be considered to prevent abrupt failure due to the unexpected rupture of non-prestressed steel bars.
- The F1FU/S1FU specimens prestressed with fully unbonded bars failed by non-prestressing reinforcement rupture during monotonic loading. Fully unbonded bars can improve the ductility of prestressed concrete beams, despite the prestressing reinforcement ratio being less than the balanced prestressing reinforcement ratio. However, from a design point, an adequate amount of non-prestressing reinforcement is essential for preventing the unexpected rupture of non-prestressing reinforcement, and to ensure the inelastic behavior of prestressed concrete beams with fully unbonded bars.
- The over-reinforced and web-confined concrete beams, prestressed by partially bonded bars, i.e., the F2PC specimen, exhibited good fatigue performance with no cracks and no reduction in beam stiffness during one million cycles. In addition, it was found that no reduction in the load-carrying capacity and beam stiffness occurred in a static test, conducted after the conclusion of one million cycles.
- Improved ductility was observed for beams prestressed with fully partially bonded CFRP bars, when compared with prestressed beams that have fully bonded CFRP bars. Over-reinforced and web-confined concrete beams, prestressed with partially bonded CFRP bars, were proposed, and evaluated to possess good fatigue capacity and durability based on the experimental results.
Author Contributions
Funding
Conflicts of Interest
References
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Specimen ID | Test Type | Prestressing Reinforcement Ratio (ρ/ρb) | Initial Prestressing | Unbonded Length (mm) | Web Confinement (mm) |
---|---|---|---|---|---|
F1FU | Fatigue test | 1.6 | 0.33 fpu | Fully unbonded | N/A1 |
F1PU | 1.6 | 0.33 fpu | 1400 | N/A | |
F2PC | 3.2 | 0.35 fpu | 1400 | 1300 (D6@50) | |
S1FU | Static test | 1.6 | 0.33 fpu | Fully unbonded | N/A |
S1PU | 1.6 | 0.33 fpu | 1400 | N/A | |
S2PC | 3.2 | 0.35 fpu | 1400 | 1300 (D6@50) |
Material | Diameter (mm) | Effective Area (mm2) | Yield Strength (MPa) | Ultimate Tensile Strength (MPa) | Ultimate Strain (%) | Modulus of Elasticity (GPa) |
---|---|---|---|---|---|---|
CFRP | 9.5 | 70.9 | - | 2500 | 1.83 | 136 |
Mild steel | 6 | 28.3 | 400 | 710 | - | 200 |
Test Type | Specimen ID | During Repeated Loading | During Monotonic Loading after One Million Cycles | Ductility Index (DI) | ||||
---|---|---|---|---|---|---|---|---|
Applied Load (kN) | No. of Cycles at Initial Crack | Load at Initial Crack (kN) | Ultimate Load (kN) | Failure Mode 2 | ||||
Min. | Max. | |||||||
Fatigue test | F1FU | 1.0 | 13 | 100,000 | 24.5 | 44.3 | R | 0.84 |
F1PU | 1.0 | 10 | 10,000 | 15.6 | 40.5 | C | 0.74 | |
F2PC | 1.0 | 15 | No cracks | 24.5 | 69.5 | C | 0.80 | |
Static test | S1FU | N/A 1 | N/A | 20.6 | 42.3 | R | PF 3 | |
S1PU | N/A | N/A | 9.8 | 37.1 | C | 0.77 | ||
S2PC | N/A | N/A | 18.6 | 67.0 | C | 0.78 |
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Jeong, Y.; Kim, W.; Gribniak, V.; Hui, D. Fatigue Behavior of Concrete Beams Prestressed with Partially Bonded CFRP Bars Subjected to Cyclic Loads. Materials 2019, 12, 3352. https://doi.org/10.3390/ma12203352
Jeong Y, Kim W, Gribniak V, Hui D. Fatigue Behavior of Concrete Beams Prestressed with Partially Bonded CFRP Bars Subjected to Cyclic Loads. Materials. 2019; 12(20):3352. https://doi.org/10.3390/ma12203352
Chicago/Turabian StyleJeong, Yoseok, WooSeok Kim, Viktor Gribniak, and David Hui. 2019. "Fatigue Behavior of Concrete Beams Prestressed with Partially Bonded CFRP Bars Subjected to Cyclic Loads" Materials 12, no. 20: 3352. https://doi.org/10.3390/ma12203352
APA StyleJeong, Y., Kim, W., Gribniak, V., & Hui, D. (2019). Fatigue Behavior of Concrete Beams Prestressed with Partially Bonded CFRP Bars Subjected to Cyclic Loads. Materials, 12(20), 3352. https://doi.org/10.3390/ma12203352