Strength Degradation of Wood Members Based on the Correlation of Natural and Accelerated Decay Experiments

An accelerated decay test and a natural decay test were conducted synchronically to explore the strength degradation of decaying wood members under long-term exposure to natural environment.A natural decay test was carried out to measure the bending strength,compressive strength parallel to grain and modulus of elasticity of the wood members,with 6 groups of specimens decayed in natural environment for 3 to 18 months respectively.To compare with corresponding decay test,in which 6 other groups of specimens were measured under accelerated conditions.The experimental data collected were evaluated by Pearson productmoment for the correlation.The results indicate that the mechanical properties of the accelerated decay were highly correlated with those in natural environment,both of which decreased in the same trend.Under the given test conditions,the mean value of the accelerated decay test data were curve-fitted to achieve the time-dependent degradation model of the bending strength,the compressive strength parallel to grain,as well as the modulus of elasticity.Due to the high correlation,the acceleration shift factors(ASF)of the two tests were derived,where the bending strength of 2.934,the compressive strength parallel to grain of 2.519 and the elastic modulus of 2.346 were employed to formulate the strength degradation models in the long-term natural environment.The results verify that the exponential function
σ=σ0e^(-βt)enables to exactly capture the degradation of the mechanical properties of wood members decayed in natural environment.

Decay Detection of Ancient Wood Rafters in Tibet by Stress Wave Testing Method

Visual classification and stress wave non-destructive testing technology were adopted to evaluate the decay status of ancient Populus wood members (rafters) replaced from the Potala Palace. The decay status of wood members was evaluated by stress wave testing and visual observation. For most of the ancient wood members, the evaluation results by two methods were consistent with each other. Also stress wave testing techniques can find the internal wood member decay to eliminate the hidden hazard for ancient wood members, and offer relatively accurate quantitative information for the safety status of ancient wood members. Thus during the maintaining for ancient architectures, visual observation combined with stress wave testing techniques is a good way to evaluate the degradation of ancient wood members.