Retrofitting Masonry Walls Using CFRP

Retrofitting Masonry Walls Using CFRP

Figure 1: Unreinforced masonry walls

Introduction:

Masonry buildings which are of high architectural and historical importance are one of the most seismically vulnerable structures in the rural areas of the world. Many of these buildings are in danger of failure because of reasons such as:

  1. Inadequate construction methods and improper materials
  2. Lateral loads like earthquakes and wind loads
  3. Foundation settlement
  4. Corrosion and environmental deterioration
  5. Change in the usage of the building
  6. Not designed according to the requirements of the recently upgraded seismic codes

In figure 2, several failure modes of unreinforced masonry (URM) walls have been observed.

Figure 2: In-plain failure modes of unreinforced masonry wall under earthquake

Retrofitting Masonry Walls Using CFRP

1- Sliding shear failure

Retrofitting Masonry Walls Using CFRP

2- Diagonal shear

Retrofitting Masonry Walls Using CFRP

3- Rocking

Retrofitting Masonry Walls Using CFRP

4- Toe crushing

Different Methods Of Seismically-Strengthening Masonry Walls:

1. Ferrocement

2. Shotcrete

3. Centre core

4. Post-tensioning

5. Application of thin, galvanized steel strips

6. CFRP

In the following table some disadvantages have been mentioned:

Retrofitting Masonry Walls Using CFRP

Strengthening methods such as shotcrete and ferrocement add considerable mass to the existing structure, which beams, columns or arches cannot tolerate. Adding such mass to an existing structure will result in increased seismic forces which the structure had not been designed for, and the probability of structural collapse during an earthquake will increase.

Why Choose CFRP for Strengthening URM Walls?

  1. The main advantage of applying externally bonded CFRP to URM walls is improving their in-plain and out-of-plain behavior. In an earthquake, human injuries or deaths in buildings in the vicinity of walls are a result of out-of-plain failure of the URM walls and the falling of debris from walls. CFRP is the best option for retrofitting such walls due to improving the out-of-plain behavior of the wall.
  2. CFRP does not add significant mass to the structure so in an earthquake it is a preferable strengthening solution.
  3. CFRP-strengthened masonry walls have higher lateral resistance, and the increase of lateral resistance is due to its higher compressive strength.
  4. Increased lateral resistance of masonry walls strengthened with diagonal CFRP strips is 115%, while this amount for masonry walls strengthened with steel strips is 58%. ¹
  5. The lateral displacement of CFRP-strengthened masonry walls at failure is 4.28 times higher than unreinforced walls. ¹
  6. The displacement ductility of CFRP-strengthened masonry walls is 1.97 times higher than unreinforced walls.
  7. The cracked, CRFP-strengthened URM walls will gain stiffness which leads to higher seismic demand
  8. The out-of-plain resistance of CFRP-strengthened masonry walls is 10-32 times the weight of the walls. ³
  9. The in-plain resistance of CFRP-strengthened masonry walls increases by a factor of 1.7 and 3 respectively. ⁴
  10. One-sided retrofitting is a successful method of repair as well; no out-of-plain or uneven response of the walls was observed. ²
  11. In some walls, debonding of the CFRP has been recorded due to different lateral load levels in the range of 50-80% of the ultimate load resistance. ²

The results obtained from the aforementioned studies point to the conclusion that, for the sake of structural, mechanical and seismic response of the masonry walls, CFRP is preferable to other techniques of reinforcing URM walls.

Retrofitting Masonry Walls Using CFRP
Retrofitting Masonry Walls Using CFRP

Figure 3: CFRP-strengthened masonry wall by Rhino Carbon Fiber™ products

Retrofitting Masonry Walls Using CFRP

Figure 4: CFRP-strengthened masonry wall by Rhino Carbon Fiber™ products

Authors

Parastoo Azad and Dr. Mehrtash Soltani (April 8, 2021)

References

1. S. H. Farooq, M. I. (2012). Response of Masonry Walls Strengthened with CFRP and Steel Strips. Arabian Journal for Science and Engineering volume 37, 545–559.

2. Mohamed A. ElGawady, M., Lestuzzi, P., & Badoux, a. M. (2005). In-Plane Seismic Response of URM Walls Upgraded with FRP. Journal of Composites for Construction.

3. Ehsani, M. R., Saadatmanesh, H., & Velazquez-Dimas, a. J. (1999). Behavior of Retrofitted URM Walls under Simulated Earthquake Loading. Journal of Composites for Construction.

4. Schwegler, G. a. (1996). Earthquake resistance of masonry structures strengthened with fiber composites. World Conf. on Earthquake Engneering.

5. Abrams, D. P. (2001). Flexural behavior of retrofitted masonry piers. KEERC-MAE joint seminar on risk mitigation for regions of moderate seismicity.