Detection of Fracture in Steel Members of Building Structures by Microstrain Measurement
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International Journal of Steel Structures (2020) 20(5):1720–1729 https://doi.org/10.1007/s13296-020-00408-3
Detection of Fracture in Steel Members of Building Structures by Microstrain Measurement Jun Iyama1 Received: 2 September 2019 / Accepted: 8 September 2020 / Published online: 16 September 2020 © The Author(s) 2020
Abstract This paper discusses a possibility of detecting structural damage caused by an earthquake, by measuring the time history of the strain of beams and columns before and/or after the earthquake. An index called “local stiffness” is defined as the ratio of section force amplitude to representative displacement amplitude, and this ratio can be physically interpreted as stiffness. By calculating section force amplitude at a section or node from the measured strain amplitude under a microtremor or small aftershocks and comparing it with the results of a static pushover analysis, it becomes possible to detect any structural damage, such as fractures. This methodology was applied and the microstrain data of a steel moment frame were measured in a large-scale shaking table test; beam-end fractures were observed after some excitation tests. After the beam-end fracture formed, the measured local stiffness dropped significantly below the analysis value, indicating the possibility of employing this value to detect fractures using the analysis value as a threshold value. Keywords Structural health monitoring · Strain gage · Shaking table test · Microtremor
1 Introduction Structural health monitoring (SHM) is a research field that has received considerable attention. SHM has been applied especially for bridge structures, and many projects that monitor the dynamic behavior of large bridges, such as Akashi Kaikyō Bridge (Sumitro et al. 2001), and Tamar Bridge (Cross et al. 2013), have been carried out. SHM of building structures too is gradually gaining popularity. For example, in recent years, some commercial monitoring systems for building structures have been marketed and increasingly applied to high-rise buildings and large-scale structures. However, compared to bridge structures, the application of SHM for building structures is still limited. One possible reason may be the limited monitoring information obtained considering the high cost of such measurement. In such monitoring systems, the floor response acceleration of a building is measured, and the displacement or other indexes are calculated. It is possible to detect some change in the * Jun Iyama [email protected]‑tokyo.ac.jp 1
Department of Architecture, Graduate School of Engineering, The University of Tokyo, 7‑3‑1 Hongo, Bunkyo‑ku, Tokyo 113‑8654, Japan
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natural frequency, the damping factor of the building, or the mode shape of the vibration. However, understanding the kind of structural damage indicated by the change and determining whether the building is damaged still remain a challenge. Arakawa and Yamamoto (2004) performed long-duration monitoring of response floor acceleration of a 120-m-high 23-story steel
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