Behaviour of joints with bonded-in steel bars loaded parallel to the grain of timber elements

This paper presents an experimental programme conducted to investigate the structural capacity of bonded-in steel bars loaded parallel to the grain in standard straight elements of natural timber. Tensile pull-out tests were conducted to examine the effect of bar diameter, bonded length and bar type (deformed and threaded steel bars) on the structural capacity of the connection. Pull-out tests on timber blocks in which the bars were deliberately misaligned in the holes were also tested to account for the fact that in real situations bars may not be perfectly centralised in the holes. The pull-out test results showed that bar diameter, bonded length and bar type considerably affected the structural capacities of the bonded-in steel joints. The results were compared with some established design equations.

Research highlights
► The best structural performance was obtained with 16 mm threaded bar bonded 300 mm into the timber blocks.
► The 12 mm and 16 mm deformed bars recorded more splitting failures than the corresponding threaded bars.
► Average shear stress at the timber/adhesive interface decreased as the bonded length increased.
► The pull-out capacity predicted by Riberholt design equation was the most consistent with that of the experiment.