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Use of Stress Waves for Measuring Surface Cracks in Mass Concrete
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:||
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.
|Appears in Collections:||土木工程學系所|
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