Glued-in CFRP and GFRP rods in block laminated timber subjected to monotonic and cyclic loading

Abstract

Current advances in timber engineering with the use of timber at longer spans necessitate the use of high performance joints. Glued-in rods exhibit high axial load capacity and stiffness and are suitable for such applications. FRP rods can increase their durability and fire performance but ways to produce progressive failure mechanisms are necessary to enhance their resilience. In this study CFRP and GFRP rods glued in block laminated timber with epoxy are investigated under both monotonic and cyclic loading. Joints with constant glue-line thickness and variable bond-line geometry are studied to induce progressive resin failure mechanisms. A stepped wedge shaped geometry with varying glue-line thickness and a mirrored version were investigated. The effect of elastic modulus (CFRP vs GFRP) and glue-line thickness on the bond strength, stiffness and material viscous damping are explored. CFRP rods exhibit 11% higher axial load capacity under monotonic loading but GFRP rods exhibit higher bond stiffness at the serviceability stage. The cyclic loading does not discount the bond performance and results in higher stiffness due to viscoelastic creep deformation. An increase in glue-line thickness results in higher axial withdrawal capacity and viscous material damping. Specimens with a wedge shaped bond-line exhibit superior mechanical performance. An FEA model is presented for a variable bond-line geometry and the numerical results agree well with the experimental findings.