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古蹟建築木材含水率測定法之相關係數及其對超音波傳遞速度之影響

Relationship between Moisture Contents Measured by Different Methods and Effect of Moisture Content on Ultrasonic Velocity of Wood Species Used in Listed Historical Buildings of Taiwan

摘要


本研究採用高週波式含水率計、電阻式含水率計與超音波等非破壞檢測儀器進行國內古蹟建築木材含水率與超音波縱向傳遞速度之檢測,一方面探究不同含水率計所測得含水率與應用絕乾法反推所測得含水率之間的相關性,結果可應用於古蹟建築木構件損壞調查時含水率之檢測與校正,以提供古蹟建築木構件含水率的正確訊息;另方面探討含水率變化對超音波速之影響,提供挑選不同含水率下古蹟修復用新木料力學性質評估之依據與校正。研究結果顯示,在纖維飽和點(含水率約25~35%)以下,以電阻式含水率計檢測所得之含水率與應用絕乾法反推所測得之含水率較為接近,所以舊木料含水率之檢測以電阻式含水率計較為適當。隨木材之脫濕過程進行,其超音波速度會隨含水率之下降而增加,二者呈一顯著之二次式相關。隨木材含水率之下降,其超音波速度之增加,在纖維飽和點以上範圍較緩,而在纖維飽和點以下範圍則增加較為明顯。本研究中採用之木材含水率與超音波傳遞速度校正之研究方法,可適用於古蹟建築木料材種之研究。

並列摘要


The main purpose of this study was to better understand the relationship between moisture contents measured by different methods and the effect of moisture content on ultrasonic velocity of wood species used in the listed historical buildings of Taiwan. Various nondestructive testing instruments were performed in this study. The results from our research could be applied for the moisture content investigation (and correction) of used wood members and for the mechanical investigation (and correction) of new wood members in the restoration of our listed historical buildings in Taiwan. Results are summarized as follows: (1) Below the fiber saturation point of wood (about 25~35%), the predicted moisture content from electrical resistance moisture meter (Delmhorst RDM-2S) was closer to the moisture content measured by oven-drying method according to CNS 452. Thus, Delmhorst RDM-2S could be suitable for investigating the moisture content of used wood member in the listed historical buildings of Taiwan. (2) In the moisture desorption process of wood, the ultrasonic velocity increased with the decrease of moisture content of wood and this relationship could be significantly regressed by a 2nd polynominal equation. (3) Above the fiber saturation point, the ultrasonic velocity increased slowly with the decrease of moisture content of wood. However, the ultrasonic velocity increased significantly with the decrease of moisture content of wood within the fiber saturation point. (4) The research methods for the investigation and correction of moisture content and ultrasonic velocity of tested wood species could be applied for other common wood species used in the listed historical buildings of Taiwan.

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