Mechanical characterization of wooden dowels with emphasis on shear strength : An experimental study on birch and beech dowels

The most common way to join timber members in structural applications is by using steel fasteners and plates offers a lot of advantages. One of the disadvantages is the environmental impact, where the production of steel contributes to a lot of emissions. An alternative solution would be to substitute the steel fasteners with wooden dowels. The next generation of Eurocode 5 (prEN 1995-1-1, 2023) proposes design equations for joints with wooden dowels. This study investigates the mechanical properties of hardwood dowels made out of birch and beech. The mechanical properties were evaluated by assessing the stiffness of the dowels experimentally in a modal analysis. Then, the shear strength of the dowels were evaluated experimentally by performing static tests in a set up made out of aluminum with two shear planes. In total, 60 birch dowels and 30 beech dowels were tested in different configurations.The results showed that the highest strength was in the radial direction, as expected. The results also showed that the beech dowels possessed higher strength compared and that the yield stress of the dowels were not depending on the diameter of the dowel. It was also found that the shear span that simulates the plastic hinges that forms in the embedment material, denoted Lfree, had a rather large impact on the material behaviour and the yield strength of the dowels, showing that the strength decreased as Lfree increased. By comparing with previous studies that performed similar tests with wood as embedment, it was found that Lfree = d is usually the length of the plastic hinges and that the results using Lfree = d were similar regardless of embedment material. The correlation between the shear strength and the axial modulus of elasticity EAX and the bending modulus of elasticity around the radial and tangential axis EBR and EBT were generally above 50%, although some outliers affected the correlations and it was therefore difficult make conclusions. It was evident that the density is a good predictor of strength, as the correlation was high and consistent. Design equations in the next generation of Eurocode 5 (prEN 1995-1-1, 2023) was compared with the experimental results, and it was concluded that prEN 1995-1-1 (2023) results in conservative values, which can be explained due to the actual failure mode that occurs in the dowels is a combination of both shear and bending, which seems to be disregarded in prEN 1995-1-1 (2023).