# Influence of Externally Bonded CFRP on the Shear Behavior of Strengthened and Rehabilitated Reinforced Concrete T-Beams Containing Shear Stirrups

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## Abstract

**:**

## 1. Introduction

#### 1.1. Literature Overview

#### 1.2. Paper Objectives and Significance

## 2. Materials and Methods

#### 2.1. Material Properties

#### 2.1.1. Concrete and Steel

#### 2.1.2. CFRP

#### 2.1.3. Epoxy Resin (Adhesive)

#### 2.2. Test Specimens

#### 2.2.1. Specimen Details

#### 2.2.2. Test Groups

#### 2.3. Strengthening and Rehabilitation Process

#### 2.4. Test Setup

## 3. Theoretical Calculations

_{n}is the nominal shear strength, V

_{c}is the nominal shear strength provided by concrete with steel flexural reinforcement, V

_{s}is the nominal shear strength provided by steel stirrups, ${\mathsf{\Psi}}_{f}$ is a strength reduction factor for CFRP (0.95 for completely wrapped members or 0.85 for three-side and two-opposite-sides schemes), and V

_{f}is the nominal shear strength provided by CFRP.

_{c}and V

_{s}were calculated according to the ACI 318−19 [38], while the contribution of the carbon fiber was calculated according to ACI 440.2R−17 [37] based on the following equations.

_{fv}is the area of FRP shear reinforcement with spacing s, f

_{fe}is the effective stress in the FRP, α is the angle of application of the primary FRP reinforcement direction relative to the longitudinal axis of the member, d

_{fv}is the effective depth of FRP shear reinforcement, S

_{f}is the center-to-center spacing of the FRP strips, n is the number of plies of FRP reinforcement, t

_{f}is the nominal thickness of one ply of FRP reinforcement, and w

_{f}is the width of FRP reinforcing plies.

## 4. Results and Discussion

#### 4.1. General Behavior and Failure Modes

#### 4.2. Experimental Shear Capacity

#### 4.3. Experimental Load–Deflection Behavior

#### 4.4. Theoretical Results

## 5. Conclusions

- The results clearly indicate that using externally bonded CFRP laminates and sheets in T-beams is effective in improving the shear capacity.
- For the strengthening and rehabilitation of RC T-beams, the failure to be expected is either pure shear cracks propagated to the tension face of the T-beam, CFRP debonding failure, or CFRP rapture failure associated with cover separation.
- The shear capacity increased for the strengthened T-beams by a range of 26–100%. The highest increase was recorded for the horizontal CFRP strips scheme.
- The shear capacity increased for the preloaded T-beams by a range of 21–73%. The highest increase was recorded for the horizontal CFRP strips scheme.
- The capacities of the strengthened beams were higher than those of their corresponding preloaded T-beams; however, there was no big difference between the experimental results of the strengthening and rehabilitation of T-beams as long as the preloaded T-beams were not loaded with more than 60% of their design capacity. After loading the beams up to 60% of the ultimate load, the dial gauge returned to zero deflection and all beams returned to their initial condition; thus, it is concluded that no significant damage occurred.
- For the experimental load–deflection curves, all T-beams exhibited almost linear trends with different slopes.
- The deflection recorded with the use of CFRP was lower than that of the control T-beam at any load values; however, the deflection at failure was not always lower than that of the control T-beam.
- The ACI 440.2R−17 does not differ between the strengthening and rehabilitation of T-beams. Moreover, not all the parameters are considered logically in the calculations; thus, the theoretical results are not always conservative in predicting the shear capacity and the provisions need to be revised.
- The theoretically predicted values according to the ACI 440.2R−17 and the experimental results did not have the same pattern of ordering the highest capacities.

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 2.**Beams groups: (

**a**) control group 1; (

**b**) inclined 45° CFRP-group 2; (

**c**) horizontal straight CFRP-group 3; (

**d**) U-wrap CFRP-group 4.

**Figure 7.**Experimental load–deflection curves for all beams: (

**a**) inclined—group 2; (

**b**) horizontal straight strips—group 2; (

**c**) U-wrapped sheets—group 3.

Requirement | Result (%) | Standard Values | ||
---|---|---|---|---|

Min | Max | Min | Max | |

Fineness (Blaine) (cm^{2}/g) | 4500 | 5000 | ||

Soundness (mm) | 0.5 | 2 | 10 | |

Initial setting time (min) | 130 | 165 | 60 |

Cement (kg/m^{3}) | Water (kg/m^{3}) | Coarse Aggregates (kg/m^{3}) | Fine Aggregates (kg/m^{3}) |
---|---|---|---|

375 | 180 | 1042.97 | 754.178 |

Tested Average Yield Stress (MPa) | Tested Average Ultimate Stress (MPa) | Elastic Modulus (GPa) | Elongation |
---|---|---|---|

550 | 680 | 200 | 14 |

Property | MasterBrace LAM | MasterBrace FIP |
---|---|---|

Modulus of elasticity (GPa) | >210 | 230 |

Tensile strength (GPa) | >2.8 | 4.9 |

Density (g/cm^{3}) | 1.6 | 1.76 |

Thickness (mm) | 1.4 | 0.166 |

Property | Value | |
---|---|---|

Compressive Strength at 25 °C (BS 6319 part 2) | day 1 | 40 MPa |

day 7 | 65 MPa | |

Flexural strength at 25 °C (ASTM C 580 part 7) | day 7 | 20 MPa |

Tensile Strength at 25 °C (BS 6319 Part 7) | day 7 | 10 MPa |

Pot life in Minutes | at 25 °C | 50 |

at 40 °C | 30 | |

Recoat time in Hours | at 25 °C | 8 |

at 40 °C | 6 | |

Bond Strength | <2 MPa (concrete failure) | |

Setting time at 25 °C | 12 h | |

Meets the requirements of ASTM C881 Type 1 Grade 3 Class B & C |

Property | Value | |
---|---|---|

Product Chemistry | MasterBrace^{®} SAT 4500 Part A | Epoxy Resin |

MasterBrace^{®} SAT 4500 Part B | Epoxy Hardener | |

Color | Blue | |

Mixed density | 1.02 kg/liter | |

Viscosity | 1500–2500 mPa·s | |

Compressive strength TS EN 196 (7 days) | >60 MPa | |

Flexural strength TS EN 196 (7 days) | >50 MPa | |

Bonding strength to concrete (7 days) | >3.0 N/MPa | |

Pot life | 30 min | |

Fully cured at 20 °C | 7 days |

Label | Definition |
---|---|

CB | Control sample: T-beam with no CFRP attached |

S-Inc | T-beam strengthened with 45° inclined CFRP attached |

R-Inc | T-beam preloaded with 45° inclined CFRP attached |

S-Str | T-beam strengthened with horizontal straight strips of CFRP attached |

R-Str | T-beam preloaded with horizontal straight strips of CFRP attached |

S-Sh | T-beam strengthened with U-wrap CFRP sheets attached |

R-Sh | T-beam preloaded with U-wrap CFRP sheets attached |

Sample | Experimental Shear Capacity (kN) | Increase (%) | |
---|---|---|---|

CB | 160 | 0% | |

S-Inc1 | 195 | 22% | 26% |

S-Inc2 | 207 | 29% | |

S-Inc3 | 204 | 28% | |

R-Inc1 | 200 | 25% | 21% |

R-Inc2 | 193 | 21% | |

R-Inc3 | 186 | 16% | |

S-Str1 | 320 | 100% | 100% |

S-Str2 | 317 | 98% | |

S-Str3 | 324 | 103% | |

R-Str1 | 279 | 74% | 73% |

R-Str2 | 285 | 78% | |

R-Str3 | 268 | 68% | |

S-Sh1 | 225 | 41% | 41% |

S-Sh2 | 219 | 37% | |

S-Sh3 | 232 | 45% | |

R-Sh1 | 205 | 28% | 28% |

R-Sh2 | 199 | 24% | |

R-Sh3 | 211 | 32% |

Sample | Experimental Shear Capacity (kN) | Theoretical Shear Capacity (kN) | Percent Increase (%) | |
---|---|---|---|---|

CB | 160 | 157.6 | 1% | |

S-Inc1 | 195 | 231.2 | −19% | −15% |

S-Inc2 | 207 | 231.2 | −12% | |

S-Inc3 | 204 | 231.2 | −13% | |

R-Inc1 | 200 | 231.2 | −16% | −20% |

R-Inc2 | 193 | 231.2 | −20% | |

R-Inc3 | 186 | 231.2 | −24% | |

S-Str1 | 320 | 308.9 | 3% | 4% |

S-Str2 | 317 | 308.9 | 3% | |

S-Str3 | 324 | 308.9 | 5% | |

R-Str1 | 279 | 308.9 | −11% | −11% |

R-Str2 | 285 | 308.9 | −8% | |

R-Str3 | 268 | 308.9 | −15% | |

S-Sh1 | 225 | 217.5 | 3% | 3% |

S-Sh2 | 219 | 217.5 | 1% | |

S-Sh3 | 232 | 217.5 | 6% | |

R-Sh1 | 205 | 217.5 | −6% | −6% |

R-Sh2 | 199 | 217.5 | −9% | |

R-Sh3 | 211 | 217.5 | −3% |

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**MDPI and ACS Style**

Abdel-Jaber, M.
Influence of Externally Bonded CFRP on the Shear Behavior of Strengthened and Rehabilitated Reinforced Concrete T-Beams Containing Shear Stirrups. *Fibers* **2021**, *9*, 87.
https://doi.org/10.3390/fib9120087

**AMA Style**

Abdel-Jaber M.
Influence of Externally Bonded CFRP on the Shear Behavior of Strengthened and Rehabilitated Reinforced Concrete T-Beams Containing Shear Stirrups. *Fibers*. 2021; 9(12):87.
https://doi.org/10.3390/fib9120087

**Chicago/Turabian Style**

Abdel-Jaber, Mu’tasime.
2021. "Influence of Externally Bonded CFRP on the Shear Behavior of Strengthened and Rehabilitated Reinforced Concrete T-Beams Containing Shear Stirrups" *Fibers* 9, no. 12: 87.
https://doi.org/10.3390/fib9120087