PSI - Issue 64

Lim Boon Xuan et al. / Procedia Structural Integrity 64 (2024) 791–798 Lim et al./ Structural Integrity Procedia 00 (2019) 000–000

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Fig. 3. (a) Time series of temperatures; (b) Time series of deflections.

3. Data preprocessing and analysis 3.1. Bridge profile and monitoring data

The data of this paper is collected from the Xiamen bridge, the first strait bridge constructed in China, linking Xiamen Island to the Jimei District of Xiamen. This multi-span box girder bridge consists of a total of 46 spans, each 45m in length, separated into 5 independent parts. The bridge SHM system is installed at the third part of the bridge as shown in Fig. 2, which consists of 12 spans. In this paper, data collection focuses on temperature data and deflection data. The deflection sensors and girder temperature sensors are installed inside the girder at the midspan, while the ambient temperature sensor is installed on the guardrail of the bridge. A total of 90 days of data were collected across July, August and September in 2022, at a sampling rate of 1 seconds. The different types of temperature data are illustrated in Fig. 3(a), while deflection data are illustrated in Fig. 3(b). To prove the effectiveness of the model for deflection prediction across different spans of the bridge, span-1 and span-6 which are located at the outermost and middlemost span respectively, are selected for validation. The ambient temperature is denoted as ܶ ௔ , girder temperature of span-1 and span-6 are denoted as ܶ ௦ and ܶ ௜ respectively, while the span-1 deflection and span-6 deflection are denoted as ܦ ௦ and ܦ ௜ respectively. 3.2. Separation of temperature-induced deflection Despite prior papers using hourly or minutely averaging method to extract temperature-induced deflection (Yue et al., 2021; Sun et al., 2019; Yang et al., 2018), in this paper, to avoid eliminating valuable information from the deflection data during the separation of temperature-induced deflection, hourly averaging or minutely averaging will not be considered. Therefore, EMD was adopted to separate the temperature-induced deflection. The EMD processed deflection outputs multiple IMFs, each containing a different range of frequencies. For instance, Fig. 4(a) shows the different IMFs output from the EMD-processed deflection of span-1. The first IMF comprises the highest frequency component in the original signal, with frequencies decreasing in the subsequently IMFs. Fig. 4(b) and Fig. 4(c) illustrate the comparison between the EMD-processed deflection and the raw deflection of span-1 and span-6

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Fig. 4. (a) Intrinsic mode functions (IMFs) of span-1 deflection; Extracted temperature-induced deflection of: (b) Span-1; (c) Span-6.