# Masonry Columns Confined by Steel Fiber Composite Wraps

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Test on Masonry Columns

#### 2.1. Test Matrix

Specimen | Shape of Cross-section | Matrix Type | Reinforcement Type | Reinforcing Scheme |
---|---|---|---|---|

1 | octagonal | - | - | - |

2 | square | - | - | - |

3 | square | epoxy | Type 1 | Continuous wrap |

4 | square | epoxy | Type 1 | Continuous wrap |

5 | octagonal | epoxy | Type 2 | Continuous wrap |

6 | octagonal | epoxy | Type 2 | Discontinuous wrap |

7 | octagonal | epoxy | Type 2 | Continuous wrap |

8 | octagonal | epoxy | Type 2 | Discontinuous wrap |

9 | octagonal | epoxy | Type 1 | Continuous wrap |

10 | octagonal | epoxy | Type 1 | Discontinuous wrap |

11 | octagonal | epoxy | Type 1 | Continuous wrap |

12 | octagonal | epoxy | Type 2 | Discontinuous wrap |

13 | octagonal | epoxy | Type 1 | Discontinuous wrap |

14 | octagonal | epoxy | Type 1 | Continuous wrap |

15 | octagonal | epoxy | Type 2 | Discontinuous wrap |

16 | octagonal | epoxy | Type 2 | Continuous wrap |

17 | square | epoxy | Type 1 | Continuous wrap |

18 | square | epoxy | Type 1 | Continuous wrap |

19 | square | epoxy | Type 1 | Discontinuous wrap |

20 | square | epoxy | Type 1 | Discontinuous wrap |

21 | square | epoxy | Type 1 | Discontinuous wrap |

22 | square | epoxy | Type 1 | Discontinuous wrap |

23 | square | epoxy | Type 1 | Discontinuous wrap |

**Figure 1.**Geometry of cross-sections of masonry columns (dimensions in mm)

**(a)**square cross-section;

**(b)**octagonal cross-section.

**Figure 3.**

**(a)**Cleaning of the column surfaces;

**(b)**Application of a first layer of matrix;

**(c)**Application of a unidirectional SRP sheet;

**(d)**Application of a second layer of epoxy resin or cementitious mortar.

#### 2.2. Mechanical Characterization of Materials

#### 2.3. Cord Characterization

Type 1 | Type 2 | |
---|---|---|

Cord sectional area (mm^{2}) | 0.621 | 0.811 |

Tensile strength (MPa) | 3199 | 2396 |

Elastic Modulus (MPa) | 160,000 | 143,000 |

Ultimate strain (%) | 1.55 | 1.16 |

#### 2.4. Epoxy Resins

#### 2.5. Bricks

Number of Samples | 4 |

Tensile Strength (MPa) | 25.21 |

Young Modulus E (MPa) | 4510 |

Number of Samples | 5 |

Compressive Strength (MPa) | 65.54 |

Young Modulus E (MPa) | 4634 |

#### 2.6. Mortar

## 3. Test Setup

## 4. Experimental Results

#### 4.1. Square Cross-Section Masonry Specimens

Series | Specimen | Volumetric ratio λ (%) | Average max compression load P (kN) | Average compressive strength (MPa) | Normalized strength P_{confined}/P_{unconfined} | Average load peak axial strain |
---|---|---|---|---|---|---|

Unconfined | 2 | - | 708 | 11.91 | 1.00 | 0.007 |

S-3X2-C | 3, 4, 17, 18 | 0.60 | 1510 | 26.65 | 2.24 | 0.0225 |

S-3X2-D | 19, 20, 21, 22, 23 | 0.40 | 1189 | 19.88 | 1.67 | 0.017 |

**Figure 7.**Failure modes of square cross-section column:

**(a)**unreinforced specimens;

**(b)**reinforced specimens.

#### 4.2. Octagonal Cross-Section Masonry Specimens

**Figure 10.**Failure modes of octagonal cross-section column:

**(a)**unreinforced specimens;

**(b)**reinforced specimen (continuous wrap);

**(c)**reinforced specimens (discontinuous wrap).

Series | Specimen | Volumetric ratios λ (%) | Average max compression load P (kN) | Average compressive strength (MPa) | Normalized strength P_{confined}/P_{unconfined} | Average load peak axial strain |
---|---|---|---|---|---|---|

Unconfined | 1 | - | 719 | 14.0 | 1.00 | 0.0085 |

O-3SX-C | 5, 7, 16 | 0.47 | 1361 | 26.6 | 1.90 | 0.0166 |

O-3SX-D | 6, 8, 12, 15 | 0.31 | 1293 | 25.2 | 1.80 | 0.0128 |

O-3X2-C | 9, 11, 14 | 0.62 | 1289 | 25.2 | 1.79 | 0.0117 |

O-3X2-D | 10,13 | 0.41 | 1224 | 23.9 | 1.71 | 0.0127 |

## 5. Design

_{mcd}) for members confined with FRP subjected to a lateral confining pressure (f

_{1}) can be written as follows:

_{md}represents the design compressive strength of unconfined masonry, k’ is a non-dimensional coefficient and f

_{1}’ is the effective lateral confing pressure. The coefficient k’ can assume different values, according to the material and the typology of the applied reinforcement. For FRP reinforcement, the value of k’ is indicated as g

_{m}/1250 where g

_{m}is the specific weight of masonry expressed in kg/m

^{3}.

_{1}’ is expressed in the Standard as:

_{eff}is the effectiveness coefficient. This value is the product between two terms: k

_{H}and k

_{V}related to the horizontal and vertical effectiveness. The effectiveness coefficient k

_{eff}depends on the values of the effectively confined volume V

_{c,eff}to the total volume V

_{m}. The horizontal coefficient k

_{h}takes into consideration the percentage of confined area of a wrapped section (Figure 13 and Figure 14), while the vertical effectiveness coefficient k

_{V}covers the effect of discontinuous wrapping throughout the column axis.

_{m}is the total (gross) cross sectional area of the wrapped member.

_{V}=1, whereas for discontinuous wrap, the vertical effectiveness coefficient is equal to:

_{fb,rid}:

_{a}and γ

_{f}represent environmental conversion factor and partial factor as suggested by CNR code; ε

_{fk}is the characteristic axial strain of composite; E

_{f}is the Young modulus of the SRP sheet; ρ

_{f}is the wrapping ratio depending on the thickness of the composite layer t

_{f}:

_{f}is the width of the wrapping along the vertical direction (fibers are supposed to be at 90° with respect to the principal axis of the masonry column), b is the highest dimension of the cross-section and p

_{f}is the spacing length between two consecutive SRP sheets measured vertically.

Series | k_{eff} | f_{1} | f’_{1} | Maximum compression load P_{theoretical} (kN) | Maximum compression load P_{experimental} (kN) | P_{experimental} /P_{theoretical} |
---|---|---|---|---|---|---|

S-3X2-C | 0.497 | 13.95 | 6.93 | 1400 | 1510 | 1.07 |

S-3X2-D | 0.315 | 7.11 | 2.83 | 952 | 1189 | 1.24 |

## 6. Conclusions

## Acknowledgements

## References

- Mastrodicasa, S. Dissesti Statici Delle Strutture Edilizie: Diagnosi, Consolidamento, Istituzioni Teoriche; Ulrico, H., Ed.; Sottotitolo: Milano, Italy, 1983. [Google Scholar]
- Ilyas, M.; Farooq, S.H.; Qazi, A.U.; Umair, R. Masonry confinement using steel strips. Pak. J. Eng. Appl. Sci.
**2009**, 5, 1–9. [Google Scholar] - Krevaikas, T.D.; Triantafillou, T. Masonry confinement with fiber-reinforced polymers. J. Compos. Constr.
**2005**, 9, 128–135. [Google Scholar] [CrossRef] - Triantafillou, T.C. Strengthening of masonry structures using epoxy-bonded FRP laminates. J. Compos. Constr.
**1998**, 2, 96–104. [Google Scholar] [CrossRef] - Corradi, M.; Borri, A.; Grazini, A. Confinement of brick masonry columns with CFRP materials. Composites Sci. Technol.
**2007**, 67, 1772–1783. [Google Scholar] - Aiello, M.A.; Sciolti, S.M. Bond analysis of masonry structures strengthened with CFRP sheets. Constr. Build. Mater.
**2006**, 20, 90–100. [Google Scholar] - Micelli, F.; De Lorenzis, L.; La Tegola, A. FRP-confined masonry columns under axial loads: Experimental results and analytical model. Masonry Int. J.
**2004**, 17, 95–108. [Google Scholar] - Di Ludovico, M.; D’Ambra, C.; Prota, A.; Manfredi, G. FRP confinement of tuff and clay brick columns: Experimental study and assessment of analytical models. J. Compos. Constr.
**2010**, 14, 583–596. [Google Scholar] - Bieker, C.; Seim, W.; Stürz, J. Post-strengthening of masonry columns by use of fiber-reinforced polymers. In Presented at the 3rd International Conference of Composites in Infrastructure, San Francisco, CA, USA, 2002.
- ASTM D 638—10 Standard Test Method for Tensile Properties of Plastics; ASTM International—American Society for Testing and Materials: West Conshohocken, PA, USA, 1995.
- ASTM D 695M—Standard Test Method for Properties of Rigid Plastics; ASTM International—American Society for Testing and Materials: West Conshohocken, PA, USA, 1991.
- CNR-DT 200—Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Existing Structures; Italian Council of Research (CNR): Rome, Italy, 2004.
- General rules for reinforced and unreinforced masonry structures. In EN 1996-1-1 Eurocode 6: Design of Masonry Structures; CEN—European Committee for Standardization: Brussels, Belgium, 2005; Part 1-1.

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**MDPI and ACS Style**

Borri, A.; Castori, G.; Corradi, M.
Masonry Columns Confined by Steel Fiber Composite Wraps. *Materials* **2011**, *4*, 311-326.
https://doi.org/10.3390/ma4010311

**AMA Style**

Borri A, Castori G, Corradi M.
Masonry Columns Confined by Steel Fiber Composite Wraps. *Materials*. 2011; 4(1):311-326.
https://doi.org/10.3390/ma4010311

**Chicago/Turabian Style**

Borri, Antonio, Giulio Castori, and Marco Corradi.
2011. "Masonry Columns Confined by Steel Fiber Composite Wraps" *Materials* 4, no. 1: 311-326.
https://doi.org/10.3390/ma4010311