The aim of the project is to monitor the detailed strain mode shapes of a full-scale civil structure, the KW51 railway bridge, in operational conditions and investigate the potential of strain mode shapes for vibration-based monitoring (VBM). To this end, the deck of the bridge is instrumented with a dense grid of multiplexed FBG macro-strain sensors as a proof of concept. For a time period of more than a year, the natural frequencies and strain mode shapes have been automatically identified every hour from the low-amplitude operational and free vibration strain data. The results demonstrate the feasibility and accuracy of the strain monitoring methodology developed by researchers of KU Leuven in field conditions. Furthermore, the temperature influence on the natural frequencies and modal strains of this full-sized civil structure with complex boundary conditions and large temperature fluctuations has been investigated. Small but clear influences are found for the natural frequencies, while the strain mode shapes are insensitive to temperature, an important conclusion, since a temperature-insensitive dynamic characteristic can be directly used for damage identification, without requiring data normalization. Furthermore, during the monitoring period, the investigated bridge underwent a retrofit. The influence of this retrofitting on the natural frequencies and strain mode shapes is investigated and compared with the temperature influence. As this retrofitting resulted in global mass and stiffness changes of the structure, it is found to have an influence mainly on the natural frequencies, except when it induces an interaction between previously well-separated modes: in that case the strain mode shapes are also affected.
- Type of the structure: Steel single-span tied arch railway bridge
- Measured parameters: Dynamic strains and temperature (temperature measured with thermocouples)
More information about the project is available in Chapter 6 of the PhD thesis of Dimitrios Anastasopoulos (link see project website).