| 摘要 |
PROBLEM TO BE SOLVED: To provide a method and an apparatus especially suited to a large- sized welded structure such as a bridge or the like and capable of detecting whether a crack is generated early, certainly and easily. SOLUTION: A crack detector is equipped with a mechanism for feeding air to the interior 11a of a structural member 11 under pressure to hermetically seal the same in the structural member, a pressure sensor for measuring the internal air pressure of the structural member and a display part for displaying the internal air pressure. The structural member 11 is constituted of a hollow base material 16 and the end members 17a, 17b for closing both ends of the hollow base material 16 and the measured value P of the internal air pressure of the structural member 11 measured by the pressure sensor 4 is monitored. When a crack is generated in the structural member 11 and pierces the wall of the structural member 11, the internal air pressure lowers and the measured value P thereof lowers. The change of the measured value P displayed on a display part 15 is judged from the display of the display part 15 to detect the generation of the crack.
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