Key Technology Research On Material Performance And Damage Detection For Wooden Components Of Ancient Chinese Building

Timber-frame structures are major part of Chinese ancient buildings. Due to the biomass characteristics of wood and the situation of exposing to the natural environment, the wooden components in Chinese ancient buildings often confront the risks of material properties declining and internal defects in long-time applied process. These risks are not only cause the hidden dangers for the integral structure security of ancient buildings, but also cause many typal components which carried lots of authenticity information vanished quickly. Thus, obtaining the material properties and internal defects information of ancient wooden components by some reasonable testing method as real as possible, is a crucial and urgent way to judging the safety and health conditions, implementing the preventive conservation, conducting the scientific repairing work, and structuring the data information platform of conservation works.Based on the analysis and discussing about the current situation and the research status, some old wooden components torn down from Chinese ancient buildings were utilized as the research objects, and some research on the suitable testing technical process and data statistical method, which by the trial approach, based on non-destructive testing technology, and for the material properties and internal defects of wooden components, were carried out.Firstly, some basic theoretical knowledge of Chinese ancient timber building and its components were discussed in three levels, which are macro level(research on the Chinese ancient building), meso level(the research on the wood characteristics), and micro level(research on the damage types and their causes in wooden components). The contents includes the development course and module components of Chinese ancient timber building, the mechanical properties and material requirements of wooden components, the characteristics of structural wood and the survey of frequently-used wood species in Chinese ancient timber building, the influence factors of wooden components durability, and the common damage forms of wooden components, etc. Thereby, the research objects of this study were deeply analyzed.Secondly, the working principles and typical types of some primary non-destructive testing technologies used for wood were listed. By using the facilities screening test and considering the wood characteristics and the spot testing requirements, the research approaches which combined the Stress-waves testing technology with the Resistance testing technology were confirmed.Thirdly, the main experiment of this study was designed within two parts, some technologies for detecting the material properties and internal damages of wooden components in Chinese ancient timber building were studied respectively:1) By performing the non-destructive test and mechanical test for test-piece respectively, the prediction models between the non-destructive testing data and the main material properties of wood(Density, MOR, MOE, UCS) were built. Some diverse statistical approaches(Liner regression model, Fuzzy information diffusion model) were utilized to inspecting their feasibility and accuracy of data prediction. On this basis, the influence rules of diverse conditions(Age, Moisture content, Drill speed) on the non-destructive testing data were studied, and the conversion formulas were built respectively, to meet the spot test requirement in different conditions.2) By using the method of reverse simulation test, some artificial penetrating holes and cribriform holes making up different proportional areas of the old wooden components’ cross-section were chiseled, to simulate the hollow and decay in real situations. By stress-waves testing, the identification accuracy of 2D analog images to the different types of damage were investigated. And the function relationships were built by comparing the actual hole area and imaged area by stress-waves. And then, based on the analysis of attenuation tendency of stress wave velocities among different propagation paths, the Mahalanobis distance discrimination model was adopted, for the estimation of the internal defects present in the component’s cross-section. By using the resistance test via crossed paths, the attenuation part of resistance curves were calculated, to modify the imaged area by stress-waves test more precisely.At last, based on the research findings, and combining with the actual spot working situations, the spot testing technical process of ancient timber buildings was established, which includes the testing range and contents confirmation, sampling method and testing method confirmation, and the specific spot operational process. The spot testing work of Long Corridor in Temple of Heaven was introduced as a sample. Regarding the current situation of heritage work and testing data application,a imformation platform for ancient building conservation work was constructed,to realize the ancient building imformation(including the testing data) can be networked application. Regarding the real problems during the spot testing work, a fixed bay device dedicated for Resistograph spot testing work was developed, try to solve the problems of measurement error, holding fatigue and cannot be fixed.