Figure 1- Schematic view of RC concrete cracks

RC walls with openings

When there are openings along concrete walls, the load paths will be altered. Due to stress concentration around openings, cracks at the corners of the openings will appear. As a result, the ultimate strength of the wall and its load-bearing capacity will be reduced. Small and large openings reduce the axial strength of RC walls by about 36% – 50%. ¹ As a result, walls with openings need to be strengthened.

Traditional strengthening technique of walls with openings

One common and traditional strengthening technique is embedding steel bars at the corners of the openings (vertical, horizontal or diagonal steel bars can be used depending on the size of the opening). Note that in the corners, the steel bars used should be at least equal to the size of the original steel rebar used beneath the concrete. The total area of these steel bars should be distributed along the sides of the wall openings.
Figure 1- Typical RC wall opening reinforcement

Strengthening wall openings with externally bonded CFRP

Strengthening wall openings with externally bonded CFRP is becoming increasingly popular.
CFRP-strengthened walls increase the ultimate strength by 14% – 60% in one-way RC walls and 3% – 41% in two-way RC walls, depending on the CFRP quality and layout. ²

CFRP layout around openings at the tension face:

  • Applying CFRP at a 45° angle to the opening’s corners
  • Applying CFRP along the four sides of the opening
CFRP applied at a 45° angle to the corners of wall openings is more effective in reducing principal stress. ³ In addition, its load-bearing capacity is higher than the wall strengthened all around the openings.
Figure 2- CFRP layout around wall opening
  • However, for a one-way wall, applying CFRP all around the openings provides higher ultimate strength when compared with 45° CFRP due to the increased strengthening of the weakest parts of the wall ⁴
  • Strengthening walls with CFRP will avoid buckling of the reinforcement
  • If your wall is cracked, it will continue to get worse over the next few years. It is better to fix it when the wall is not bowing rather than after a large bow occurs
Rhino Carbon Fiber™ has products designed to fix this problem. For more information, refer to https://cutt.ly/ojAuDrZ .
Parastoo Azad and Dr. Mehrtash Soltani (February 11, 2020)
  1. Popescu, G. S. (2017). Concrete Walls with Cutout Openings Strengthened by FRP Confinement. Journal of Composites for Construction, 04016106.
  2. Lima, J.-H. D. (2019). Experimental Study on RC Walls with Opening Strengthened by Externally Bonded CFRP. Journal of Composites for Construction, 04019008.
  3. Mohammed, B. S. (2013). One way RC wall panels with openings strengthened with CFRP. Construction and Building Materials, 575-583.
  4. Lima, M. M.-H. (2016). The effects of CFRP orientation on the strengthening of reinforced concrete structures. The Structural Design of Tall and Special Buildings, 759-784.