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Creep of timber joints

J.W.G. van de Kuilen
Delft University of Technology, The Netherlands
CNR Trees and Timber Research Institute, San Michele all'adige (TN), Italy

A creep analysis has been performed on nailed, toothed-plates and split-ring joints in a varying uncontrolled climate. The load levels varied between 30% and 50% of the average ultimate short term strength of these joints, tested in accordance with ISO 6891. The climate in which the tests were performed varied between about 40% and 90% relative humidity, which coincides with Service classes 1 and 2 of Eurocode 5 for timber structures. A large scatter in creep factors was found with the highest average creep values for the 30% load levels. In order to analyse the influence of moisture variations, a creep model was developed containing the effects of mechanical creep, the influence of yearly shrinking and swelling as well as mechano-sorptive creep. Furthermore, a method has been presented in order to be able to derive creep factors to be applied in design calculations, based on the creep factors determined in laboratory creep tests, taking into account the design stiffness values for these joint types.

Key words: Nails, toothed-plate, split-rings, joints, mechano-sorptive effects, creep factors