Bond-slip behaviour of CFRP-timber joints: The role of strip width, length, and anchor in historical and new wood

Abstract

The bond-slip behaviour between carbon fibre reinforced polymer (CFRP) and timber plays a crucial role in the structural performance of strengthened wood elements. This study investigates the bond-slip characteristics of CFRP–timber interfaces by evaluating the effects of wood type, CFRP strip width, strip length, and fan-type anchor arrangements, where mechanical anchors with radially expanding ends are used to improve the bonding performance. Single-lap shear tests were conducted on both historical (old) and newly sourced wood to determine the influence of material properties on bond strength and load transfer mechanisms. Digital Image Correlation (DIC) was utilized to capture full-field displacement and strain distributions along the bond interface, providing a detailed assessment of debonding mechanisms. Additionally, an analytical study was conducted to develop generalized equations for the proposed bond-slip model, offering a comprehensive understanding of interface behaviour. The results indicate that strip width has a more pronounced impact on bond performance compared to strip length, significantly increasing load-carrying capacity and energy absorption. Anchor implementation effectively delays debonding and enhances bond performance, with increasing anchor rows and columns improving stiffness and load resistance. However, beyond a certain threshold, excessive anchoring slightly reduces energy dissipation due to constrained deformation capacity. These findings highlight the necessity of optimizing CFRP strengthening configurations to maximize structural efficiency while maintaining a balance between strength, stiffness, and ductility. The insights obtained contribute to the development of more effective reinforcement strategies for both modern and heritage timber structures.