The Influence of CFRP Sheets on the Load-Bearing Capacity of the Glued Laminated Timber Beams under Bending Test
Abstract
:1. Literature Survey
2. Research Significance
3. Materials and Methods
3.1. Materials
3.2. Lamination Process
3.3. Bending Test
3.4. X-ray Computed Tomography Test
4. Results
4.1. Load-Bearing Capacity
4.2. X-ray Computed Tomography Analysis
5. Conclusions
- In the Glued Laminated Timber beams subjected to bending, the dominant failure was the failure caused by the exceeding of the limit tensile stresses, and the crack occurred on the bottom surface of the beam. The most common type of failure was the breaking of the bottom fibers in the tensile zone, which was rarely accompanied by shear.
- CFRP-reinforced beams exhibit linear elasticity until the moment of failure. Strengthening the bottom surface of a beam by gluing a composite allows its ability to absorb tensile stresses to be extended, which leads to an increase in the load-bearing capacity and ductility of the beam. During the conducted experiment, there were no breaks in the reinforcement fibers.
- The computed tomography examination before the application of the load, and also after the destruction of the beams, enabled the very good integrity between the beams and CFRP to be confirmed—regardless of the number of reinforcement layers, the laminate did not detach.
- It was noticed that the number of CFRP laminate layers has an influence on the mechanism of failure. For the beams reinforced with three and five layers, the dominant failure mechanism began with a crack at the connection of the wood and the adhesive layer in the support zone. This is related to the phenomenon of the concentration of interfacial shear and pull-off stresses. In practice, this phenomenon may have a negative impact on the final strength of reinforced elements.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Nomenclature and Symbols
fm,g,k | bending strength of the GL28h spruce wood |
ft,0,g,k | tensile strength of the GL28h spruce wood |
fc,0,g,k | compressive strength of the GL28h spruce wood |
E0,g,mean | mean value of modulus of elasticity of the GL28h spruce wood |
ft,cf | tensile strength of carbon fiber mats (MPa) |
elastic modulus of the carbon fiber mats (GPa) | |
elongation at break of the carbon fiber mats (%) | |
elongation at break of the epoxy resin (%) | |
Eer | modulus of elasticity in flexural of the epoxy resin (GPa) |
Ft,er | tensile strength of the epoxy resin (MPa) |
F | destructive force (kN) |
l | span of the beam (m) |
u | vertical displacement of the beam (mm) |
equivalent stiffness within the displacement range of 2–6 mm (Nm2) | |
CV | coefficient of variation (%) |
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Parameter | Value |
---|---|
Source voltage | 60 kV |
Source current | 900 μA |
Voxel size | 70 μm |
Filter | none |
Exposure time | 250 ms |
Number of X-rays used to reconstruct a 3D image | 3200 |
Number of CFRP Reinforcement Layers | Specimen No. | ||||||||
---|---|---|---|---|---|---|---|---|---|
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | ||
0 | F (kN) | 24.55 | 17.67 | 18.61 | 18.09 | 17.75 | 18.6 | 17.67 | 17.54 |
u (mm) | 10.46 | 7.80 | 8.32 | 10.69 | 11.24 | 10.29 | 9.99 | 9.97 | |
EI (Nm2) | 13,224 | 11,450 | 11,808 | 9615 | 11,309 | 11,072 | 9171 | 9354 | |
1 | F (kN) | 17.68 | 26.46 | 26.64 | 25.21 | 24.55 | 25.32 | 23.97 | 25.50 |
u (mm) | 9.70 | 13.55 | 13.69 | 13.29 | 13.50 | 13.88 | 14.42 | 15.08 | |
EI (Nm2) | 8989 | 12,733 | 11,250 | 10,420 | 9473 | 13,246 | 10,961 | 10,157 | |
3 | F (kN) | 18.80 | 25.50 | 22.05 | 22.29 | 23.74 | 22.17 | 23.43 | 22.59 |
u (mm) | 11.37 | 16.22 | 10.83 | 12.47 | 12.81 | 11.82 | 12.27 | 12.92 | |
EI (Nm2) | 10,042 | 9181 | 10,929 | 9784 | 9762 | 9314 | 9928 | 14,278 | |
5 | F (kN) | 16.15 | 23.43 | 17.29 | 24.86 | 26.77 | 27.31 | 26.17 | 26.94 |
u (mm) | 8.46 | 10.86 | 7.68 | 11.84 | 9.92 | 9.58 | 9.44 | 9.01 | |
EI (Nm2) | 8843 | 11,098 | 10,724 | 12,594 | 13,218 | 14,069 | 14,968 | 16,357 |
Number of CFRP Reinforcement Layers | |||||
---|---|---|---|---|---|
Without Reinforcement (for 7 Specimens) | 1 Layer (for 7 Specimens) | 3 Layers (for 7 Specimens) | 5 Layers (for 8 Specimens) | ||
Mean ultimate force for each beam series | [kN] | 17.99 | 25.38 | 23.11 | 23.62 |
Standard deviation | [kN] | 0.45 | 0.96 | 1.24 | 4.45 |
Coefficient of variation | [%] | 2.52 | 3.76 | 5.35 | 18.84 |
Mean value of the bending moment for each beam series | [kNm] | 2.04 | 2.88 | 2.62 | 2.68 |
Average value of the increase in the load-bearing capacity of the beams reinforced with CFRP in relation to the reference beams | [%] | - | 41.07 | 28.46 | 31.29 |
Type of Beam | Failure Mode (Scheme 1 to 7 according to De la Rosa) | Dominant Course of Failure | Detachment of the Reinforcement |
---|---|---|---|
Reference beam From 0/1 to 0/8 | 3 (tension)—7 times 6 (shear)—1 time | Fracture at the border of a growth ring (tangent)—delamination, tearing of the bottom fibers, destruction initiated and running through knots | not applicable |
One layer of reinforcement from beam 1/1 to 1/8 | 5 (shear)—6 times 6 (shear)—1 time 4 (shear + tension) + 2 compression—1 time | Shear of the cross-section-destructive longitudinal crack above the knot line, spreading from the center, fracture at the border of a growth ring (tangent)—delamination from the center towards the support or delamination going to the knot in the middle of the span | no |
Three layers of reinforcement from beam 3/1 to 3/8 | 6 (shear)—7 times 7 (no visible breakage)—1 time | Shear of the bottom part of the cross-section in the support zone, which runs to the center of the beam and passes through a knot (right next to the support), delamination of the beam | no |
Five layers of reinforcement from beam 5/1 to 5/8 | 5 (shear)—5 times 6 (shear)—3 times | Shear of the bottom part of the cross-section in the support zone, which runs horizontally to the center or which runs through the entire beam to the opposite top part of the cross-section, partial adhesive failure at the wood-glue interface, delamination of the element | no (6 times) a part next to a support (2 times) |
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Śliwa-Wieczorek, K.; Ostrowski, K.A.; Jaskowska-Lemańska, J.; Karolak, A. The Influence of CFRP Sheets on the Load-Bearing Capacity of the Glued Laminated Timber Beams under Bending Test. Materials 2021, 14, 4019. https://doi.org/10.3390/ma14144019
Śliwa-Wieczorek K, Ostrowski KA, Jaskowska-Lemańska J, Karolak A. The Influence of CFRP Sheets on the Load-Bearing Capacity of the Glued Laminated Timber Beams under Bending Test. Materials. 2021; 14(14):4019. https://doi.org/10.3390/ma14144019
Chicago/Turabian StyleŚliwa-Wieczorek, Klaudia, Krzysztof Adam Ostrowski, Justyna Jaskowska-Lemańska, and Anna Karolak. 2021. "The Influence of CFRP Sheets on the Load-Bearing Capacity of the Glued Laminated Timber Beams under Bending Test" Materials 14, no. 14: 4019. https://doi.org/10.3390/ma14144019
APA StyleŚliwa-Wieczorek, K., Ostrowski, K. A., Jaskowska-Lemańska, J., & Karolak, A. (2021). The Influence of CFRP Sheets on the Load-Bearing Capacity of the Glued Laminated Timber Beams under Bending Test. Materials, 14(14), 4019. https://doi.org/10.3390/ma14144019