Distribution of stresses along the length of BFRP rods glued-in to Irish Sitka Spruce

Glued-in rods (GiR) present a viable alternative to traditional steel moment connections in both new build and retrofit of timber structures. Limited research has been carried out on the distribution of stresses along the... [ view full abstract ]

Glued-in rods (GiR) present a viable alternative to traditional steel moment connections in both new build and retrofit of timber structures. Limited research has been carried out on the distribution of stresses along the glued length of a rod under a load combination of axial force and bending moment. Previous research has found that under an axial-only load with short embedded lengths the entire length of the rod reaches peak stress at once and fails at a relatively low load with high peak stress. At longer embedded lengths failure is more gradual, with one end reaching peak stress before the other leading to a higher failure load and lower peak stress. This research aims to confirm that this holds for combined loading also; that stresses are not distributed evenly along the embedded length of a GiR and that failure arises at the loaded end due to a peak in stress concentration at this location. Electrical Resisting Strain gauges and Draw Tower Grating fibre optic sensors were used to capture the stress profile along the length of the GiR. Embedded length and edge distance were varied to investigate the effect of these variables on stress distribution. Specimens were tested under a pull-bending test set-up. Generally, a linear increase in strain was observed at each measured location until failure. In all specimens, failure was observed to occur with a stress peak towards the loaded end. In a number of specimens peak stress was observed to move away from the loaded end as the specimen approached failure, suggesting the bond at this end had failed.