| Popis: |
It has been discussed for many years whether GNSS is viable technology for Structural Health Monitoring (SHM) of super-large bridges. At present, there are two divided opinions: the first one is that GNSS is very expensive and useless because of its poor performance in structural health monitoring due to high noise level, and the opposite opinion is that it is indeed useful but needs to address some inherent issues of GNSS for high precision positioning. This paper will show how GNSS is used for SHM of the Forth Road Bridge (FRB) in Scotland during its repair cycle due to a major structural failure and re-opening. A feasibility project called GeoSHM (GNSS and Earth Observation for Structural Health Monitoring) was funded by the European Space Agency (ESA) in 2013 and led by the University of Nottingham in the UK with the objective of offering an integrated solution for assisting the maintenance decision-making process of different types of assets. It is the first time that GNSS has played a role on a service bridge during its repairing cycle: operational, failure, load tests, repair, load tests and re-opening. Thus, the real-life GNSS monitoring data under the different loading conditions, such as extremely strong wind, known traffic and testing loads, are processed and then a quasi-real time GNSS data strategy based on Fast Fourier Transform (FFT) has been developed for time-frequency analysis, with an attempt to reveal the structural health conditions of the FRB. The results demonstrate that the main natural frequencies of the FRB are quite stable in the time domain under normal or even extremely abnormal loading. Meanwhile, the FFT amplitude time series of each frequency can clearly display the influence caused by different kinds of loading respectively, such as vehicles and wind etc., which would be a reliable indicator to assess the structural health conditions and improve the serviceability of the FRB in the future. |
