Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/12988
標題: 以應力波檢測巨積混凝土結構物之表面裂縫
Use of Stress Waves for Measuring Surface Cracks in Mass Concrete
作者: 郭世芳
Fang, Kuo Shih
關鍵字: mass concrete;巨積混凝土;time-of-flight diffraction method;artificial cracks;impactor;繞射波傳輸時間法;人工裂縫;敲擊源
出版社: 土木工程學系
摘要: 
本論文的主要目的,在於延伸表面裂縫深度檢測之應用,由一般建築結構、橋樑等,到巨積混凝土結構上。為了解大粒徑骨材及深裂縫對於應力波動訊號的影響,本研究擬規劃製作三個混凝土塊體並加入直徑大於三英吋的骨材,同時預埋數道垂直裂縫,最淺為0.25m最深是1.1m,用以模擬巨積混凝土中產生的深裂縫,再對這些預埋裂縫由淺到深實施非破壞性檢測,以探討應力波動行為是否仍然適用,同時輔以數值分析。試驗結果將以時間領域為主的敲擊式繞射波傳輸時間法呈現,從紀錄到的波形觀察是否有明顯的繞射波產生,並加以變換敲擊源尺寸,探討敲擊能量是否足夠。研究結果顯示,在繞射波行經的路徑中,粗骨材所佔的比例較低,對於整個應力波波速影響不大,應力波行為與一般裂縫檢測相近;由於裂縫的深度較深,波傳路徑增長,造成直徑小(3mm~5mm)的敲擊源所導入的應力波能量明顯不足,造成的擾動振幅與雜訊相近,更加深判斷的困難度,因此,必須使用直徑較大的敲擊源進行施測。由實驗室及現場壩體之檢測,可證明敲擊式繞射波傳輸時間法對於巨積混凝土產生的深裂縫進行檢測,深具可行性及實務應用性。

The objective of the thesis is to extend the application of the detection of the depth of surface-opening cracks from general building and bridge structures to mass concrete .In order to evaluate the influences caused by big aggregates and deep surface-opening cracks on the signals, three concrete blocks were constructed as specimens. In construction of the specimens, aggregates with diameter lager than 3 inches were used. Several artificial cracks with depths ranging from 0.25 to 1.1 meters were created by inserting wooden plates into concrete. A technique called the time-of-flight diffraction method with impact-generated stress waves is adopted in this study. Numerical and experimental studies are performed to investigate the behavior of the stress waves and to ascertain if the technique is still suitable for this application. Study parameters include effect of coarse aggregate, impact energy and the displacement caused by the diffracted waves.
Numerical and experimental results show that the coarse aggregate has less influence on wave speed due to its low volumetric ratio. In addition, big steel spheres are used as impactors to generate stress waves with low frequency and enough energy for detection of deep cracks. As a result, the coarse aggregates are transparent to the low frequency waves and the displacement caused by the diffracted waves is significant and easy to identify so that there is no difficulty in detection of deep cracks. Experimental results obtained from laboratory and field show that the time-of-flight diffraction method can be successfully applied to detection of deep cracks in mass concrete.
URI: http://hdl.handle.net/11455/12988
Appears in Collections:土木工程學系所

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