A dimensionless feature for continuous bridge health monitoring with tiltmeter measurements

Abstract

Structural Health Monitoring (SHM) is an essential tool for bridges especially if they have a long period of activity. The bridge considered in this work allows the crossing of the river Po between Lombardia and Emilia-Romagna in Italy. It is about 1.2 km long and has 35 main spans: 25 simply supported beams and 10 cantilevers. The bridge, in use since 1958, underwent a closure period and extraordinary maintenance in 2019 due to severe structural problems. After reopening, the bridge is continuously monitored with a system of 88 bi-axial tiltmeters installed in May 2022. The sensors measure static inclinations (< 1Hz) providing information on the deflection and torsion of the bridge spans. The monitoring system returns a set of summary statistics for each inclination signal gathered in the last hour. Statistics like the mean are used to examine anomalous span drifts in the long term. Instead, the Interpercentile Range is used to evaluate span movements in the short term. In fact, the latter proved to be a good indicator of the hourly traffic load on the bridge, assuming a constant structure stiffness. Therefore, an SHM strategy is to monitor span movements, on a daily basis, using traffic as an active load. This makes it possible to identify any increases in bridge oscillations in relation to a reference condition, calculated over a given monitoring period. For this purpose, a dimensionless metric is proposed as monitoring feature. First, a theoretical analysis of metrics is presented. Then, results obtained from experimental bridge monitoring data are shown.