Health detection techniques for historic structures

The protection of historic buildings has drawn increasing attention and usually requires a sound nondestructive testing (NDT) technique. This paper first describes the significance of and the status on the protection of historic structures followed by a summary of common damage and repair measures for such structures. Lastly, the principles, characteristics, and applications of NDT techniques for historic wooden and masonry structures, including ultra-CT testing, stress wave testing, micro-drilling resistance meter, radar detection, and X-ray diffraction, are described and compared. This study concludes by providing a guide for studying the structural damage of historic structures and for the selection of a detection technique.

Comprehensive Evaluation Method of Historical Timber Structural Building Taking Fujiu Zhou House as an Example

Physical and mechanical properties of timber components are the basis of developing the technical measures for the conservation and restoration of historical timber structural buildings. By means of integrating on-site investigation (such as a visual survey, moisture content test, micro-drilling resistance test, and material samples collection of historical timber components) and laboratory tests, this study proposed a series of methodologies for comprehensively evaluating the physical and mechanical properties of timber. This method can be quickly mastered by various non-professionals and can help the cross-learning of various disciplines engaged in the research of architectural heritage protection. As a trial, the methodologies were applied to survey and assess a typical historical Chinese timber structural building named the Fujiu Zhou house (the house is located in No. 19, Qinglian lane, Yangzhou city, Jiangsu province, China). The paper studies the 224 components of the main structure of the building, including 128 columns and 96 beams. With the help of the components’ defects and damage status, GB/T13942.2-1992 and the National Lumber Grades Authority (NLGA), the grade of timber components was distinguished. The modulus of elasticity (MOE), modulus of rupture (MOR), and other related material properties parameters of timber components were also obtained. The trial results verify that the proposed methodologies are reasonable, and they can be helpful for the conservation of a historical timber structural building.

Assessment of Wooden Foundation Piles after 125 Years of Service

Buildings on piles have been constructed in Ljubljana since the Bronze Age. The piles were made of different types of wood. In the present study, piles that were erected about 125 years ago were investigated. Investors tend to renovate a building; therefore, the piles were analysed to assess the structural condition of the building. The building showed no signs of damage. To gain access to the piles, a 2 m thick layer of soil was removed. On-site, the following analyses were carried out: drilling resistance with a resistograph and a screw withdrawal test. Part of the piles was isolated and light microscopy, scanning electron microscopy, infrared spectroscopy, dynamic vapour sorption, density analysis, and chemical analysis were performed. Microscopic analysis revealed that the piles were made from the wood of Scots pine (Pinus sylvestris). The results indicate that the wood was severely degraded, mainly by soft-rot fungi and bacteria, resulting in a significant deterioration of its mechanical properties.

Friction correction when predicting wood basic density using drilling resistance

Basic density is a fundamental wood property of pulp and sawn wood. An IML Resi PD 400 drilling resistance tool (IML System GmbH, Wiesloch, Germany) was used to evaluate the basic density of Eucalyptus nitens discs and the impact of needle friction on basic density prediction. To determine the accuracy of that prediction with the commonly used linear drill bit shaft friction correction and determine whether this correction is linear, 40 discs were drilled radially, then cut into segments which were measured for basic density. Drilling resistance had a strong relationship with basic density in the outer wood; it was weaker at the pith but this did not compromise prediction accuracy. When using a linear friction correction, the drilling resistance underpredicts basic density by 7.6% in the first 2–3 cm after stem entry, after which the prediction error ranged from 0.6–1.9%. The friction correction was found to be nonlinear, especially at the first few centimeters. To apply this friction correction, basic density values from the model should be added to predict basic density values until 2.9 cm from Resi entry point and after that subtracted to account for the drill bit shaft friction.

Research of On-Site Screening and Non-Destructive Testing for Damaged Wooden Components of the Long Corridor in Temple of Heaven

Take the Long Corridor in Temple of Heaven as an example, some screening and testing process for its wooden components which have damaged was recommended. By pre-knocking survey, the wooden components which probably have damaged were screened out and as the important focus. Then, some non-destructive testing methods such as stress-wave testing and micro-drilling resistance testing were utilized. By the comparison, analysis and interaction correction for the testing images, the internal damaged situation of wooden components were obtained. Three typical types of wooden components were selected in this study, and some specific and suitable non-destructive testing methods which adapt to their position characteristic were discussed. Thus, it can give some useful suggestions and data supporting for the later repairing and management works.