| Summary: | 博士 === 國立成功大學 === 建築學系碩博士班 === 95 === Wooden structural frames of historical buildings in Taiwan, such as those used in wood truss houses of Japanese and western styles and the traditional buildings of the Han people, are the main structures affecting the structural safety of the buildings. In order to maintain the historical importance of the buildings, it is therefore very important to use proper methods to maintain the structures for conservation. In addition, the styles of the master carpenters are substantially expressed in the design and construction of wooden frames, the architectural forms, and the materials and decorations used in the buildings. In particular, the color-rich paintings on the wooden structural components represent the excellence of the art of traditional craftsmen and artists and are very valuable historical masterpieces. However, these objects to be preserved often need to be repainted onto new wood materials due to the damage to the old wooden components, leading to the loss of historical and cultural treasures. One of the keys to this issue is the conservation of wooden structural frames. They are not merely principal structures but are also very valuable pieces of traditional art, and represent an index of the life of historical buildings.
To preserve such important cultural properties, an inspection of the wooden structural frames is required before conservation. Only when the damaged area and degree of destruction have been located and examined, and the condition of the wooden structural frames verified, can an appropriate procedure for conservation be proposed. Following preservation principles, the use of Nondestructive Evaluation (NDE) techniques can meet the demand for assessment of structural safety without damage to the materials, which are then allowed to maintain their integrity for the future.
This study first discusses the damage appearance, types and location, and the common materials and structure material dimensions used for the wooden structural components of historical buildings. Several common NDE techniques currently used in Taiwan are then reviewed, to form an appreciation of their limitation and validity. Furthermore, this study attempts to establish useful information for quantitative evaluation of the wooden structural frame via practical experiment using scientific devices and by comparison of their practicability and convenience. The results are then optimized and applied to the structural safety analysis of full-scale structural timber to generate useful procedures for the evaluation of preservation and conservation methods for historical buildings
For the application of the ultrasonic wave testing technique for examination of wooden structural frames, this study performed static bending testing on stimulated damaged specimens or small clear specimens. Other comparisons include the differences between different testing methods, the effect of the different outer materials coated on the wooden structural frames, and the application of different pressures on the transducers of the devices for a change of ultrasonic wave velocity, which are used to evaluate effective applications and their drawbacks. The results showed that ultrasonic wave technology can be effectively used in the evaluation of new materials, but it is unreliable for the old materials used in historical buildings.
For the drill resistance method, this study tested the compression perpendicular to the grain on small clear specimens. Using nondestructive inspection, a total of 18 groups of specimens with treatments of different drilling directions, different materials and grain angles of wood were tested to find their compression perpendicular to the grain. In addition, another group of specimens was used in static bending testing. The results provide a comparison of the relationships between drilling resistance values and mechanical properties, and the information can be useful for the evaluation of wood quality and testing of full-scale structural timber. The results also revealed that drilling resistance values and several mechanical properties of wood, such as crushing strength perpendicular to the grain (fc), modulus of elasticity perpendicular to the grain (Ec), and bending strength (fb), have a medium to high correlation in some groups. Regression analysis showed that between the drill resistance values and fc of the material the density prediction models can be established for the groups. An analysis of the relationship between the 45-degree radial drilling resistance value and the modulus of elasticity in static bending showed an optimal explanation model when the variable of ultrasonic wave velocity was analyzed with multiple regression analysis.
In the nondestructive evaluation of full-scale structural timber, this study applied the drill resistance and static bending tests with 40 new timbers of 15 and 18 cm in diameters and 34 used waste ones to compare the relationship between resistance values and the modulus of elasticity in static bending tests. The results showed that the 45-degree radial drilling resistance value and the modulus of elasticity in static bending of full-scale structural timber have a medium to high correlation, showing that this technique is an excellent method for the evaluation of the wooden structural frames of historical buildings. The experiment data from this study can also form the basis of relevant research on the conservation of traditional architecture.
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