The effect of displacement rate on the axial load capacity of steel rods glued into glulam beams

Glued-in rod (GiR) timber connections are being increasingly used for structural connections due to their high stiffness, axial load transmission, and connection efficiency. Studies have been conducted on various factors impacting the performance of glued-in rods, such as glue-line thickness, moisture content, and rates of loading for small loading rates. The impact of higher rates of loading is less known and is critical for understanding the connection performance under accidental loading scenarios. This study investigated the relationship between the rate of loading (ROL) and the axial withdrawal capacity of steel threaded rods (M12) bonded into softwood glulam (GL24) with a structural two-part adhesive (glue-line thickness of 2 mm). The specimens were tested in a ‘pull-pull’ configuration under four rates of loading: 1, 10, 100, and 1000 mm/min, with the latter ROL representing accidental loading. The axial withdrawal load capacity and stiffness at the serviceability and ultimate limit state were found to increase with an increase in ROL. The stiffness was found to be more sensitive to loading rates, as determined by a one-way ANOVA analysis. The design equations for the axial withdrawal load capacity and stiffness at the serviceability from the new draft version of Eurocode 5 did not agree well with the experimental findings. Rate of loading modification factors were proposed to account for instantaneous loading scenarios.