| 種別 | paper |
| 主題 | MEASUREMENT OF INELASTIC FLEXURAL DEFORMATION AT A CRACK IN A BEAM |
| 副題 | |
| 筆頭著者 | Muhammad Akram Tahir（University of Engineering and Technology, Lahore, Pakistan） |
| 連名者1 | Tamon UEDA（University of Tokyo） |
| 連名者2 | |
| 連名者3 | |
| 連名者4 | |
| 連名者5 | |
| キーワード | |
| 巻 | 12 |
| 号 | 2 |
| 先頭ページ | 831 |
| 末尾ページ | 834 |
| 年度 | 1990 |
| 要旨 | INTRODUCTION Deflection of a flexurally cracked beam is usually estimated by assuming averaged flexural stiffness over cracked zone like in the Branson's formula. Actual stiffness along beam axis, however, varies greatly. Rotation at a crack is quite different from that between cracks. How to estimate the rotation at a crack has not been commonly known yet because there is lack of experimental data largely due to difficulty in measurement of the rotation at a crack.. Recently a kind of optical metrology, "laser speckle technique", has been applied to measurement of concrete displacement. In laser light natural roughness of surface, like concrete surface, produces speckle, which is very strong contrast of light. When speckle is photographed, the image of a speckle is a pin hole on a film. If the film is double-exposed before and after movement of the concrete surface, the speckle images on the film cause an interferometry phenomenon, called Young's fringe. Magnitude and direction of the movement of the concrete surface can be measured from spacing and direction of the Young's fringe. The laser speckle technique enables to measure displacement at any point in a plane. When displacement needs to be measured at a very small interval or when location of measuring displacement is uncertain, the laser speckle technique becomes a powerful tool. The measurement of rotation at a flexural crack, which is considered to be localized at the crack, is the case in which the measurement at a very small interval is vital. CONCLUDING REMARKS (1) Flexural deflection of a reinforced concrete beam can be measured accurately with precision of 0.001mm by the laser speckle technique. (2) The laser speckle technique enables to take measurement at an interval of a couple of millimeter, so that very localized deformation like inelastic rotation at a flexural crack can be measured. (3) It was observed that inelastic component of flexural deflection in the tested beam was caused by very localized deformation, called inelastic rotation right at a flexural crack. To know the relationship between moment and rotation (or moment and curvature) at a flexural crack is very important to estimate flexural deflection. Since the observed crack spacing was unusually large in this study, the observed moment-rotation relationship may not be applied to the cases with ordinary crack spacing. The results with ordinary crack spacing as well as crack height-rotation relationship will be presented in the near future. |
| PDFファイル名 | 012-01-2140.pdf |