In the field of structural rehabilitation, Carbon Fibre Reinforced Polymer (CFRP) has revolutionized how we approach the strengthening of reinforced concrete (RC) structures. However, while the short-term benefits of CFRP are well-documented, its performance under sustained, long-term loading presents unique challenges—specifically regarding interface stiffness and deflection.
When an RC beam is strengthened with an external CFRP layer, the effectiveness of the reinforcement depends entirely on the bond at the concrete-composite interface.
Structural engineers must account for two primary phenomena:
- Interface Slip: The gradual reduction in stiffness at the interface between the concrete and the carbon fibre.
- Deflection Growth: The increase in beam curvature over time due to concrete creep, shrinkage, and the loss of composite action.
Standard epoxy bonding may not be sufficient to maintain optimal interface stiffness over extended periods. The introduction of additional anchorage systems (such as U-wraps or mechanical anchors) significantly alters the performance profile:
- Mitigating Slip: Additional anchorage limits the relative slip of the external layer, ensuring that the CFRP continues to carry its intended share of the tensile load even as the concrete undergoes long-term deformation.
- Stiffness Retention: Beams with robust anchorage configurations exhibited a more stable interface, resulting in a lower rate of deflection increase compared to beams with inadequate end-treatments.
- Serviceability Limit State (SLS): Proper anchorage design is not just about preventing ultimate failure; it is a prerequisite for satisfying deflection limits in aging infrastructure.
For engineers and contractors involved in structural strengthening, it is clear: Anchorage is not an optional extra. To ensure the sustainability and durability of a CFRP intervention, the design must prioritize the effectiveness of the anchorage system to counteract long-term interface degradation.