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The mechanical property of timber is a prerequisite for the evaluation of ancient timber structures. The main mechanical properties of three kinds of timber including the old Tibetan Populus cathayana, new Tibetan Populus cathayana and new Tibetan Pine were obtained by tests in this paper. The principles and assumptions made in the determination of these strengths and the time-dependent laws on the design strength of timber in ancient Tibetan structures were discussed. It is found that the physical and mechanical properties of Tibetan Populus cathayana have degraded greatly after hundreds of years. The strength degradation of a structural component can be attributed to the decay and cracking of timber when the stress ratio is low while it can be attributed to the creep of timber caused by the load duration effect when the stress ratio is high. The new Tibetan Pine is also checked to be a good material for the restoration of ancient Tibetan building due to its higher strength compared to the old Populus timber.
Yang et al. (Sat,) studied this question.