Estimation of Creep Limit of Screw Joints between Timber and Structural Plywood under Constant Shear Loading

In a situation where the development of various novel wooden structural materials continues, it becomes necessary to understand the creep properties of wooden screw joints under shear loading. Therefore, shear creep tests for joint specimens were conducted. Screw joint specimens consisting of solid wood (Japanese cypress) and structural plywood made of softwood were used for the tests. The tests were conducted in a testing room controlled at 20 °C temperature and 65% relative humidity. The shear load was applied for over 40000 hours. The stress levels were determined as 39.0-70.2% of the standard yield load obtained by monotonic-loading tests. The slip-time relationships were obtained by the tests. This study proposed a method for estimating the creep limit by analyzing the slip-time relationships. By applying the proposed method, the creep limit of the screw joint specimens was estimated as 27.6% of the yield load.