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橋梁模態頻率與運營環境作用的相關性

Correlation of modal frequency variation for a bridge with operational and environmental actions

  • 摘要: 橋梁模態頻率隨運營環境作用的變化規律是結構健康監測的研究主題之一.根據東海大橋6 a監測數據的周期變化特性,識別了運營條件下主梁豎彎、側彎、扭轉基頻變化的影響因素,采用偏相關系數和周期平均法對比了各因素的影響程度.研究發現,東海大橋的模態頻率存在1 a、1周、1 d、12.42 h等變化周期,與結構溫度、交通荷載、風荷載、海面高度等的變化周期相吻合;結構溫度和交通荷載是引起該橋頻率變化的最主要因素,它們在各周期上的相對影響大小不同;周期平均法可有效分離監測數據中的年、周、天周期成分,揭示不同運營環境作用與頻率變化的相關性.研究結果有助于加深對橋梁運營期頻率變化的理解,從而更準確地評估結構性能.

     

    Abstract: In the vibration based structural health monitoring (VBSHM) field, the modal frequency of a structure is commonly used as an indicator for the global health condition of the structure. However, field measurements have shown that the modal frequency of a bridge varies with structural anomalies and the operational and environmental actions, e. g., temperature and traffic loading. Moreover, the latter variation usually exceeds the frequency shifts induced by the small and medium structural anomalies. To highlight the anomaly-induced frequency changes, the variability of modal frequencies of bridges with the operational and environmental actions must be investigated, and then, the action-induced frequency variations need to be eliminated. According to the periodic characteristics of the six-year monitoring data of the Donghai Bridge, this research identified the main actions that affected the modal frequencies of the first vertical/lateral bending modes and torsional mode of the girder of this bridge, and further, it compared the relative contributions of actions to the variability of frequencies through the partial correlation coefficients and the proposed cyclic averaging method. The results show that the modal frequencies of the Donghai Bridge vary at cycles as 1 a, 1 week, 1 d, and 12.42 h, which coincide with the inherent predominant cycles of structural temperature, traffic loading, wind loading, and sea levels, respectively. Structural temperature and traffic loading are the most influential factors for the frequency variation, and their relative importance is different for each individual cycle. The results also show that the cyclic averaging method can effectively separate the components in periods of 1 a, 1 week, and 1 d and can disclose the inherent correlation between actions and modal frequencies. This study helps in enhancing the understanding of the frequency variability for operational bridges and may lead to a more reliable evaluation of structural performance.

     

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