An experimental study of the effects of moisture variations and gradients in the joint area in steel-timber dowel joints

This experimental study examines the influence of moisture variations on the load-bearing capacity of steel-timber dowel joints. The glulam specimens used to manufacture the joints were first exposed to controlled climate changes. After being stored in the climate chambers, holes were drilled and dowels were inserted. Then, the joints were loaded to failure. The main aim of this study was to investigate how and to what extent moisture variations and gradients in the joint area affects the load-bearing capacity in tension parallel to the grain. The load-bearing capacity was found to be reduced under these conditions when compared to reference joints. Moreover, the brittleness of the joints increased with the time the joints had been exposed to drying. Moisture-induced stresses and cracks in the joint area were found to be a possible explanation of the results. A similar interpretation was given in other studies where other structural timber elements have been studied. This raises an important question of how such moisture effects should be considered in design codes. One possibility is to include the influence of moisture-induced stresses in the k mod factor used in Eurocode 5. Another way could be to consider this type of moisture effect as an equivalent mechanical load case.