Dynamic monitoring of a long span arch bridge

A new multi-channel dynamic monitoring system was recently installed in a long span concrete arch bridge that crosses the Douro River in the city of Porto, Portugal: the “Infante D. Henrique” bridge. This paper describes the experimental and numerical studies developed shortly after construction of the bridge, characterizes the installed monitoring system and presents the results achieved with the software developed to process the data that is continuously received through the Internet. Preliminary studies included the development of an ambient vibration test and the construction of a numerical model of the bridge that was “tuned” to fit the bridge dynamic properties identified by the ambient vibration test. The routines implemented include the on-line automatic identification of the bridge’s natural frequencies with the Frequency Domain Decomposition method, enabling the tracking of the bridge’s first 12 natural frequencies. This unique feature is only possible due to the combination of high-quality acquisition equipment with state of the art processing algorithms.