Determining Wood Density And Mechanical Properties Of Ancient Architectural Timbers With Micro-Drilling Resistance

Inspection and evaluation of timber members in ancient architectures is different from the traditional testing of wood materials in that the original state of the ancient structure should be maintained to the maximum degree by avoiding any destructive procedures. During the ancient structure inspection, in addition to detecting the internal defects of the timber members, a major challenge is to determine the wood density and residual mechanical properties of the timber members and provide an accurate data base and technical guidance for the repair and rehabilitation work of the structure.The objectives of this study were to investigate the use of a micro-drilling technique (resistograph) in the inspection and evaluation of ancient wood structures and establish empirical models for predicting wood density and mechanical properties of the timber members.Larch (Latin name) is one of most common species used in the ancient architectures in Beijing. In this study, wood samples obtained from both new and old larch timbers were chosen for laboratory experiments. Wood specimens were prepared based on GB/T1929-2009、GB/T1936.1-2009、GB/T1933-2009and GB/T1935-2009standards. Physical measurements and micro-drilling tests were first conducted on all specimens, followed by mechanical tests (bending and compression) to obtain the modulus of elasticity and modulus of rupture in bending as well as the compressive strength. Based on the experimental data, regression relationships between the micro-drilling resistance and the wood density, modulus of elasticity, modulus of rupture and compression strength were established. The results were also analyzed to examine the influences of wood moisture content, grain orientation, and decay on wood property prediction. It was found that micro-drilling resistance can be used to predict the density and compressive strength of the ancient timbers, and it can also provide reasonable reference values for the modulus of elastic and bending strength of the ancient timbers.Following the laboratory investigation, field inspection case studies were carried out on two ancient architectures in Beijing-Xiannongtan God Warehouse and Temple of Heaven Slaughter Pavilion. It has been shown through the case studies that the resistance micro-drilling technique and the regression equations developed from the experimental data can be used in field for evaluating the wood density and mechanical properties of the timbers in ancient architectures.