Nonlinear Behavior of Bonded and Unbonded Two-Way Post-Tensioned Slabs Pre-Strengthened with CFRP Laminates
Abstract
:1. Introduction
2. Research Significance
3. Experimental Procedure
4. ANSYS Finite Element Model
4.1. Main Elements Material and Modeling
- A.
- Concrete
- B.
- Steel Reinforcement and Plates
- C.
- CFRP Laminates and Epoxy Layers
- D.
- Epoxy/Concrete and Epoxy/CFRP Interfaces
- E.
- CFRP Slippage
- F.
- Bonded and Unbonded Cable Modeling
4.2. FEM Meshing
4.3. Loading and Boundary Conditions
4.4. Stepped Analysis
4.5. Model Calibration and Validation
- (A)
- Comparison of Camber
- (B)
- Applying of Initial Strain of Tendons
4.6. First Crack Monitoring
5. Results and Discussion
5.1. Load Deflection Behavior
5.2. Concrete and CFRP Strain Behavior
5.3. Failure Modes
- Concrete crushing; when the strain of concrete reaches 0.002,
- Tendon cut; due to reaching its ultimate capacity (not occurring here),
- CFRP debonding; concrete cover or CFRP laminate separation at the surface plane.
6. Parametric Study
6.1. Real Load Simulation
6.2. Different Arrangements of CFRP Laminates
6.3. PT to CFRP Strength Contribution
7. Conclusions
- The FEM simulation showed great agreement with experimental results. The ratio between the experimental and FEM results of the first cracking load varied from 0.7 to 0.9, whereas the results of the ultimate load varied from 0.8 to 1.1 and the ultimate deflections varied from 0.8 to 1.
- At different loading levels, there is a good correlation between FEM results and experimental results for CFRP strains either for the final debonding stage or for the locations of slippage.
- From both FEM and experiments, it was concluded that the failure modes of the tested slabs were concrete crushing, CFRP rupture, and/or CFRP debonding.
- Performance of the fully prestressed post-tensioned two-way slabs pre-strengthened with CFRP laminates have better performance in bonded rather than unbonded slabs.
- Strengthening using CFRP materials is extremely effective in increasing the ductility index of both bonded and unbonded PT concrete slabs. Ductility increased by 62.18% and 59.87%, respectively, when compared with the control samples.
- Real load simulation rather than test-equivalent criteria is considered a major and sensitive factor that has to be carefully represented in either experimental or numerical simulations to reflect reliable results.
- In selecting an optimized scheme for strengthening PT slabs, it is noted that using laminates adjacent to columns is more efficient than in other slab locations.
- CFRP strength contribution to PT cabling is very considerable in slabs with low PT reinforcement ratios, whereas it is not effective in slabs with larger PT ratios.
- Finally, the results that were obtained using a numerical FEM model with the ANSYS program demonstrated good agreement with experimental results for illustrated slabs.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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ID | Specimen Types | Test Parameters | |
---|---|---|---|
Type of Prestressing | Pre-Compression Ratio in (X- and Y-Direction) | ||
UN | Unbonded Control Slab | Unbonded | 1 MPa |
US | Unbonded Slab with CFRP Laminate | Unbonded | 1 MPa |
BN | Bonded Control Slab | Bonded | 1 MPa |
BS1 | Bonded Slab with CFRP Laminates | Bonded | 1 MPa |
BS2 | Bonded Slab with CFRP Laminates | Bonded | 2 MPa |
ID | Pcr KN | ∆cr mm | Pu KN | ∆u mm | ∆max mm | Strain CFRP (%) | K Initial | K Post Cracking | Ductility Index |
---|---|---|---|---|---|---|---|---|---|
UN | 177 | 1.4 | 450 | 11 | 17 | --- | 66 | 14 | 2.2 |
US | 151 | 1.71 | 403 | 24.3 | 46.8 | 38% | 88 | 11.2 | 3.6 |
BN | 179 | 3.2 | 502 | 27 | 44 | --- | 56 | 13 | 2.8 |
BS1 | 150 | 11 | 480 | 25 | 58 | 34% | 88 | 12 | 5.3 |
BS2 | 169 | 4.31 | 610 | 35.8 | 48.9 | 40% | 51.2 | 21.1 | 8.1 |
∆ Camber (Test) | ∆ Camber (ANSYS) |
---|---|
0.859 mm | 0.742 mm |
Slab ID | Cracking Load (KN) | Ultimate Load (KN) | Ultimate Deflection (mm) | ||||||
---|---|---|---|---|---|---|---|---|---|
EXP | FEM | EXP/FEM | EXP | FEM | EXP/FEM | EXP | FEM | EXP/FEM | |
UN | 177.4 | 200 | 0.9 | 450 | 420 | 1.1 | 40 | 45 | 0.9 |
US | 150.63 | 210 | 0.7 | 403.3 | 500 | 0.8 | 24.3 | 30 | 0.8 |
BN | 179.4 | 250 | 0.7 | 502 | 520 | 1 | 27 | 33 | 0.8 |
BS1 | 149.6 | 220 | 0.7 | 480 | 500 | 1.1 | 25 | 29 | 0.9 |
BS2 | 150 | 200 | 0.8 | 600 | 605 | 1 | 35 | 36 | 1 |
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Attia, M.M.; Khalil, A.H.H.; Mohamed, G.N.; Samaan, M.F.; Katunský, D. Nonlinear Behavior of Bonded and Unbonded Two-Way Post-Tensioned Slabs Pre-Strengthened with CFRP Laminates. Buildings 2023, 13, 35. https://doi.org/10.3390/buildings13010035
Attia MM, Khalil AHH, Mohamed GN, Samaan MF, Katunský D. Nonlinear Behavior of Bonded and Unbonded Two-Way Post-Tensioned Slabs Pre-Strengthened with CFRP Laminates. Buildings. 2023; 13(1):35. https://doi.org/10.3390/buildings13010035
Chicago/Turabian StyleAttia, Mohammed M., Ayman H. H. Khalil, Ghada N. Mohamed, Morcos F. Samaan, and Dušan Katunský. 2023. "Nonlinear Behavior of Bonded and Unbonded Two-Way Post-Tensioned Slabs Pre-Strengthened with CFRP Laminates" Buildings 13, no. 1: 35. https://doi.org/10.3390/buildings13010035