Structural Health Monitoring of An Aged Arch Dam Using Long-Term Continuous Observation of Ambient Vibration/Seismic Motion

Abstract eng:
Structural health monitoring technique was applied to an aged arch dam, where long-term continuous observation of ambient vibration/seismic motion was performed over a span of three years and a half and where the predominant frequency variation along time was detected, the variation during ambient vibration/seismic motion. As the result, the following was made clear; 1) The predominant frequency of the observed arch dam perpendicular to the dam axis varies with a period of one year, correlating highly with the dam surface temperature, that is, basically high in summer and low in winter. The predominant frequency of the dam in winter tends to be lower as the compressive stress is inferred to become lower caused by the contraction of the dam concrete due to the dam temperature drop. 2) The reservoir water level also affects the predominant frequency of the dam. The predominant frequency becomes lower as the reservoir water level becomes higher when the water level is higher than a certain level due to the effect of added mass. On the other hand, when the water level is lower than a certain level, the predominant frequency tends to be higher as the water level becomes higher as the joints between the dam concrete blocks close due to the water pressure increase. 3) During the main shock of the 2011 Off the Pacific Coast of Tohoku Earthquake, the observed record with very large maximum acceleration of about 630 gal was obtained at the crest of the dam. The duration of the seismic motion of the main shock ranged about three minutes. 4) Spectral analyses of the main shock record of the 2011 Off the Pacific Coast of Tohoku Earthquake and of the ambient vibration records before/after the main shock revealed that the predominant frequency during the main shock became remarkably lower than the one from the ambient vibration before the main shock, and that the predominant frequency during the ambient vibration after the main shock returned back to the one before the main shock, on the whole. 5) Thus, the following important matters were made clear, which are significant from the viewpoint of the structural health monitoring; a) The structural health of an aged arch dam can be evaluated through the monitoring of the predominant frequency variation which is detected as the result of the long-term continuous observation of ambient vibration/seismic motion and its data analysis. b) It was shown objectively by the numerical value of the predominant frequency that the structural health of the observed aged arch dam was maintained even after the main shock of the 2011 Off the Pacific Coast of Tohoku Earthquake, and also lots of its large-scale aftershocks. c) It was confirmed that the structural health of the observed arch dam was maintained and also that the seismic load unchanges through the fact that the predominant frequency of the observed arch dam unchanged before and after the large-scale earthquakes, which shows that the seismic back-check on the observed aged arch dam is unnecessary even after suffering from large-scale earthquakes.

• Export as: BibTeX | MARC | MARCXML | DC | EndNote | NLM | RefWorks
• Add to your basket