Shear Capacity of RC Beams Strengthened with Flax Fiber Sheets Grafted with Nano-TiO2
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials and Reagents
2.2. Instruments and Equipment
2.3. Characterization
2.3.1. Structural Design of RC Beams
2.3.2. FRP Strengthened RC Beams in Shear Capacity
3. Results and Discussions
3.1. Experimental Results and Analysis of the Shear Capacity of Ordinary RC Beams
3.2. Experimental Results and Analysis of the Shear Capacity of FRP-Strengthened RC Beams
3.2.1. Major Damage Phenomena and Processes
3.2.2. Characteristic Loads and Load–Span Displacement Curves
3.2.3. Strain Distribution in the Flax Fiber Sheets
3.3. Shear Capacity Model of RC Beams Reinforced with Flax Fiber Sheets
σbξh0 = ρsbh0fs
Vc = τbξh0
Vcdv = σbξh0(h0 − ξh0/2)
- τ—shear stress of the reinforced concrete (MPa);
- fc′—compressive strength of the concrete (MPa);
- σ—normal stress of the reinforced concrete (MPa);
- b—width of the reinforced concrete beam (mm);
- h0—effective height of the section of RC beam (mm);
- ξh0—ultimate height of compression zone of RC beam (mm);
- ρs—steel bars ratio of the reinforced concrete beam;
- fs—stress of the vertical steel bars under extreme conditions (MPa);
- Vc—contribution of the vertical steel bars in the concrete to the shear bearing capacity (kN);
- dv—axial distance from the mid-load point to the support point (mm);
- A, B—calculation parameters for the shear capacity of RC beams without web steel bars.
Φ = (2B + Aρsfs/fc′)/(2Bλfc′/ρsfs + 1)
A = 0.837, B = 1.075
- Vf—contribution of the flax fiber sheets to the shear bearing capacity (kN).
- Ef—elastic modulus of the FRP composites (GPa);
- ρf—clamping ratio of the FRP composites;
- εf—effective strain of the FRP composites (mm/mm).
- β—angle between the flax fiber sheets and the longitudinal axis of the RC beam (°).
- fc—concrete compressive strength design value (MPa).
- Ef—tensile modulus of the flax fiber sheets (GPa);
- tf—thickness of the flax fiber sheets (mm);
- εf—effective strain of the flax fiber sheets (mm/mm);
- wf—width of the flax fiber sheets (mm);
- sf—spacing between the center points of adjacent flax fiber sheets (mm).
- B(εf)—parameter related to the ultimate strain of the flax fiber sheets.
- Vf,exp—contribution of the flax fiber sheets and flax fiber sheets grafted with nano-TiO2 to the shear capacity of RC beams (kN).
- k, C—curve fitting parameters.
- Vexp—shear capacity of the RC beam (kN);
- λ—shear span ratio of the RC beam, λ = dv/h0.
4. Conclusions
- (1)
- Compared with unreinforced RC beams, the shear capacity and mid-span deflection of beams strengthened with flax fiber fabric sheets is greatly improved.
- (2)
- The reinforcing effect of flax fiber sheets grafted with nano-TiO2 is greater than that of unmodified flax fiber sheets. After reinforcement with ordinary flax fiber sheets, the shear capacity of RC beams is 550–579 kN, which is 45.4–53.2% higher than that of unreinforced RC beams.
- (3)
- After reinforcement with flax fiber sheets grafted with nano-TiO2, the shear capacity of RC beams is greatly improved to 653 kN, which is 72.8% higher than that of unreinforced RC beams. At the same time, the mid-range deflection of the beam reached 14.6 mm, which is 75.9% higher than that of unreinforced RC beams.
- (4)
- Taking the ultimate strain of the flax fiber sheets as a control index, the shear capacity of the RC beams after reinforcement exhibits a good linear relationship with the cuff ratio of the flax fiber sheets. An equation for calculating the shear capacity of RC beams strengthened with ordinary flax fiber sheets and flax fiber sheets grafted with nano-TiO2 was preliminarily proposed through curve fitting.
- (5)
- For the calculation of shear capacity of RC beams strengthened with the flax fiber sheet, the calculation result is in good agreement with the test result. Furthermore, it is safer. In view of the limited number of specimens in this paper, further bases for the design and calculation of this strengthened RC beam will be obtained through further tests.
Author Contributions
Funding
Conflicts of Interest
References
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Rebar Type | Grade | Diameter (mm) | Yield Strength (MPa) | Tensile Strength (MPa) | Elastic Modulus (GPa) | Elongation (%) |
---|---|---|---|---|---|---|
Vertical steel bars | HRB400 | 25 | 410 | 570 | 200 | 20.0 |
Structural steel bars | HRB400 | 14 | 410 | 565 | 200 | 21.5 |
Erecting steel bars | HRB400 | 12 | 390 | 560 | 200 | 20.0 |
Stirrup | HPB300 | 8 | 310 | 450 | 210 | 25.0 |
Crystal Phase | Average Particle Size (nm) | Purity (%) | Specific Surface Area (m2/g) | Bulk Density (g/cm3) |
---|---|---|---|---|
Anatase phase | 10 ± 5 | >99 | 200 ± 30 | 0.25–0.35 |
Graft Content (%) | Molding | Tensile Strength (MPa) | Tensile Modulus (GPa) | Inter-Laminar Shear Strength (MPa) | ||
---|---|---|---|---|---|---|
Radial | Latitudinal | Radial | Latitudinal | |||
2.34 | Hand lay-up | 297.4 | 225.6 | 6.83 | 6.61 | 48 |
Single Fiber Diameter (µm) | Tensile Strength (MPa) | Elastic Modulus (GPa) | Elongation (%) | Areal Density (g/m2) | Nominal Thickness (mm) |
---|---|---|---|---|---|
13 | 2100 | 105 | 2.1 | 800 | 0.4 |
Test Instrument and Equipment | Models | Manufacturer |
---|---|---|
High-speed static strain test analysis system | 16 aisle, DH3820 | Jiangsu Donghua Testing Technology Co., Ltd. (Jingjiang, China) |
Pressure sensor | 250 t, GD-250T | Fuzhou Jingkong Automation Equipment Co., Ltd. (Fuzhou, China) |
Linear variable differential transformer (LVDT) | 25 mm, MHR-25 | Shanghai Ruihong Testing Technology Co., Ltd. (Shanghai, China) |
Resistance strain gauges | 120 Ω, BE120-10AA 120 Ω, BQ120-60AA | AVIC Electric Instrument Co., Ltd. (Beijing, China) |
RC Beam | Fiber Sheets Type | Main Direction | Paste Layers |
---|---|---|---|
RC-FRP1 | Ordinary flax fiber sheets | Radial | 3 |
RC-FRP3 | Ordinary flax fiber sheets | Latitudinal | 6 |
RC-FRP5 | Flax fiber sheets grafted with nano-TiO2 | Radial | 3 |
RC-FRP6 | Unidirectional basalt fiber sheets | - | 1 |
Beam | P1 (kN) | δ1 (mm) | P2 (kN) | δ2 (mm) | Pu (kN) | δu (mm) | P1/Pu (%) | P2/Pu (%) | ΔPu (%) |
---|---|---|---|---|---|---|---|---|---|
RC-control | -- | -- | -- | -- | 378 | 8.3 | -- | -- | -- |
RC-FRP1 | 488 | 10.1 | 528 | 11.2 | 565 | 12.2 | 86.2 | 93.3 | 49.6 |
RC-FRP3 | 473 | 10.0 | 535 | 11.2 | 559 | 11.8 | 84.7 | 95.8 | 47.8 |
RC-FRP5 | 583 | 13.4 | 632 | 14.3 | 653 | 14.6 | 89.2 | 96.8 | 72.8 |
RC-FRP6 | -- | -- | -- | -- | 543 | 11.7 | -- | -- | 43.5 |
Beam | Resistance Strain Gauge | Strain Distribution | ||||
---|---|---|---|---|---|---|
15% | 40% | 60% | 80% | 95% | ||
RC-control | No.1 | −29.1 | −74.1 | 459.9 | • | • |
No.2 | 9.31 | −22.5 | −61.2 | 468.5 | 3368.4 | |
No.3 | 10.8 | −26.1 | −43.1 | −53.7 | 29.9 | |
No.4 | −1.1 | 16.9 | −13.2 | −7.4 | −7.6 | |
No.5 | 8.4 | −9.2 | −12.7 | • | • | |
No.6 | 16.2 | −18.0 | 12.5 | 108.5 | 768.7 | |
No.7 | −0.4 | 15.5 | 56.5 | 198.8 | 493.4 | |
No.8 | 6.5 | −28.3 | 42.1 | 165.3 | 676.0 | |
No.9 | −1.9 | 21.6 | • | • | • | |
No.10 | 39.7 | 58.4 | −217.7 | 361.4 | • |
Beam | Resistance Strain Gauge | Strain Distribution | ||||
---|---|---|---|---|---|---|
15% | 40% | 60% | 80% | 95% | ||
RC-FRP1 | No.1 | 115.2 | 127.6 | 606.1 | 971.1 | 710.0 |
No.2 | 94.6 | 111.8 | 4087.0 | • | • | |
No.3 | 301.0 | 327.0 | 364.1 | 347.4 | 367.2 | |
No.4 | 234.1 | 337.1 | 363.3 | 349.6 | 355.4 | |
No.5 | 140.9 | 221.2 | 4142.2 | 3830.4 | 4131.1 | |
No.6 | 947.5 | 982.5 | 1620.0 | 1457.4 | 1420.8 | |
No.7 | 109.2 | 116.4 | 128.2 | 102.8 | 61.9 | |
No.8 | 74.1 | 125.4 | 1803.1 | 1040.7 | 1232.9 | |
No.9 | −14.0 | −3.1 | 5204.4 | • | • | |
No.10 | −12.0 | −5.9 | 263.6 | 904.3 | 352.4 | |
RC-FRP3 | No.1 | −8.6 | −15.2 | −131.2 | −305.5 | −258.7 |
No.2 | 46.5 | 101.1 | 288.0 | 1611.2 | 2005.5 | |
No.3 | 147.5 | 244.4 | 286.1 | 1687.4 | 539.9 | |
No.4 | −3.8 | −48.0 | 95.5 | 101.2 | 70.4 | |
No.5 | 53.9 | 85.5 | 2037.7 | 2116.6 | 2465.8 | |
No.6 | 764.4 | 906.2 | 1596.5 | 3695.2 | 3803.6 | |
No.7 | 13.7 | 21.2 | 46.5 | 85.0 | 115.2 | |
No.8 | 41.1 | 48.8 | 2081.9 | 2317.5 | 4917.1 | |
No.9 | 0 | −4.1 | 1764.7 | 4020.1 | 5782.1 | |
No.10 | −3.3 | −21.0 | −70.4 | 85.7 | 297.0 | |
RC-FRP5 | No.1 | 32.9 | 26.3 | 415.3 | 2789.1 | 5234.7 |
No.2 | 33.2 | 50.7 | −24.7 | −154.7 | −181.8 | |
No.3 | 7.7 | 6.1 | 11.9 | 10.2 | 19.2 | |
No.4 | 35.8 | 50.9 | 4408.5 | 1271.5 | 403.4 | |
No.5 | 35.8 | 9.2 | 882.3 | 1696.4 | 1156.1 | |
No.6 | 12.7 | 9.9 | −7.1 | −10.1 | −17.8 | |
No.7 | −3.4 | 3.5 | −22.8 | −110.6 | −227.5 | |
No.8 | 5.5 | −18.9 | 2325.6 | 3650.9 | 4392.5 | |
No.9 | −12.2 | −26.7 | 2714.0 | 3464.9 | 4096.2 | |
No.10 | 3.9 | −22.2 | 4.2 | 147.4 | 443.6 |
Beam | Shear Bearing Capacity Test Results (kN) | Shear Bearing Capacity Specification Formula Calculation Results (kN) | Error (%) |
---|---|---|---|
RC-control | 378 | 437.5 | 15.7 |
RC-FRP1 | 565 | 471.4 | −16.6 |
RC-FRP3 | 559 | 481.2 | −13.9 |
RC-FRP5 | 653 | 484.8 | −25.8 |
Beam | Shear Bearing Capacity Test Results (kN) | Shear Bearing Capacity Model Calculation Results (kN) | Error (%) |
---|---|---|---|
RC-FRP1 | 565 | 557.4 | −1.34 |
RC-FRP3 | 559 | 569.9 | 1.94 |
RC-FRP5 | 653 | 646.3 | −1.02 |
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Wang, H.; Xian, G. Shear Capacity of RC Beams Strengthened with Flax Fiber Sheets Grafted with Nano-TiO2. Materials 2020, 13, 1430. https://doi.org/10.3390/ma13061430
Wang H, Xian G. Shear Capacity of RC Beams Strengthened with Flax Fiber Sheets Grafted with Nano-TiO2. Materials. 2020; 13(6):1430. https://doi.org/10.3390/ma13061430
Chicago/Turabian StyleWang, Hongguang, and Guijun Xian. 2020. "Shear Capacity of RC Beams Strengthened with Flax Fiber Sheets Grafted with Nano-TiO2" Materials 13, no. 6: 1430. https://doi.org/10.3390/ma13061430