Structural strengthening Q&A

Question: 

The effect of the thickness of adhesive layer on the shear stress at the interface of concrete beams strengthened with prestressed CFRP plate

Answer: 

In the technology of reinforced concrete beams with prestressed carbon fiber plate, the shear stress concentration at the plate end interface will be caused when the carbon fiber plate is laid. Excessive shear stress will cause cracks or even peeling at the bonding interface, which will cause prestress failure and peeling damage of the entire structure.

The main factors affecting the magnitude of shear stress at the bonding interface include

(1)Carbon fiber plate initial prestress level,

(2)Modulus of elasticity of carbon fiber plate

(3)Carbon fiber plate thickness

(4)Shear stiffness and thickness of adhesive layer

Through the prestressed carbon fiber plate relaxation test on the nine concrete beams, the size and distribution of the carbon fiber plate strain and the interface shear stress after prestressed relaxation were analyzed. The result shows:

(1) With the increase of the initial prestress level of carbon fiber plate, the interface shear stress at the end of the reinforced beam and plate increases, and the interface shear stress has a positive correlation with the initial prestress.

2) The thickness of the adhesive layer has a significant effect on the shear stress at the interface between the reinforced beam and the plate.

When the thickness of the adhesive layer increases from 2mm to 4mm, the interface shear stress decreases and the corresponding effective transfer length decreases. When the thickness of the adhesive layer increases to 6 mm, the interface shear stress increases instead, and the transfer length also increases accordingly.