Conference Agenda

Structural Heath Monitoring (SHM) systems for civil structures are usually designed with the aim to assess damage, following the consecutive levels of damage detection, localization, qualification, quantification, and, if possible, prediction. However, some SHM applications are not directly linked to the risk of occurrence of specific damage, but to the global performance of the civil structure to withstand the loads it was designed for. Thus, the measurements gathered by the SHM system can be distilled into Health Indicators (HI), the evolution of which through time shall provide an insight into the load effects and the capacity of the asset to sustain them, independently from the task of damage assessment. The definition of such Health Indicators may vary depending on the civil asset, the expected loads and the operational context.

Practical feedback is given from three operational case studies, involving continuous strain and vibration measurements over several years. In the Mont-Blanc Tunnel linking France to Italy through the Alps, the HI were computed from strain measurements of the intrados of the concrete slab which supports the road lanes inside the tunnel. The Vière Bridge in the French Alps, a masonry arch that withstands the effects from soil movement at its abutments, has been monitored with wireless strain sensors for eight years, using another definition of HI to track its evolution. In Greece, the Smart Bridges project involves the monitoring of a large portfolio of 250 bridges across the whole country, requiring a dedicated HI design to allow for comparative analysis among different bridges monitored with similar sets of strain and acceleration sensors. The data analysis concepts used by each HI to manage the large quantity of raw measurement data collected are discussed, as well as some operational decisions of asset management, to which the Health Indicators released by the SHM eventually contributed.

Most of Italy’s road infrastructures are now over 50 years old, reaching the end of their originally planned service life. Moreover, due to economic growth and technological progress, the actual loads they are subjected to exceed those for which they were originally designed. This causes a condition of fragility, where functional inadequacy is compounded by materials that are no longer suitable for their intended purpose.

Among the issues that most severely affect the transport system, one of the most significant is the large amount of documentation required to authorize an exceptional transport (i.e., one involving load exceeding the limits set by the Highway Code). These special loads have a considerable impact on structures, altering their behaviour and causing abnormal rotations, sometimes of notable magnitude. Bureaucratic procedures, though lengthy and costly, are therefore necessary to ensure safety in conditions of reduced structural capacity and high loads.

To streamline this process—burdensome both for transport companies and for the managing authorities—this project aims to demonstrate a potential procedure to manage heavy transportation which is based on the monitoring of structural behaviour associated to the real-time tracking of the heavy vehicles transiting on the bridge.

In detail, to demonstrate the feasibility of the proposed approach, a corridor is selected as a case study and suitable monitoring systems are designed and installed on a selected number of bridges belonging to the corridor itself. At the same time, GPS positioning systems are installed on selected heavy vehicles traveling along the corridor. These allows for precise real-time localization of each vehicle, enabling the correlation of any detected structural anomaly with the passage of a known exceptional load. Moreover, a Weight-in-motion system is installed in the neighbourhood of one if the instrumented bridges to allow keeping trace also of the traffic not belonging to the instrumented vehicles.

This paper reports the results obtained on one of the instrumented bridges, namely a bridge crossing river Adda close to the town of Pizzighettone, in the northern Italy. A proper monitoring system, combining static and dynamic sensors has been designed to track the evolution of natural frequencies and modal shapes over time and to estimate the vertical displacement of the bridge, induced both by the standard traffic and by heavy loads, through the measurement of a set of rotations.

A numerical model of the bridge has been developed and calibrated through preliminary tests, allowing to simulate different scenarios in terms of damages and load. By correlating the real response and that of the numerical model, it is possible to identify potential permanent damages induced by the transit of a heavy vehicle, to characterize bridge degradation by tracking the response to similar loads over time and based on the current state of the structure, to update the maximum allowable load.

The D14 bridge is a three-span prestressed concrete aircraft bridge built in 1970, with a deck wider than it is long (326 m x 59 m) that carries the first runway (09R/27L) of the Charles de Gaulle (CDG) airport over the A1 highway. Now subjected to substantial dynamic loads from modern aircraft of several hundred tonnes travelling at high speed during take-off and landing, the structure requires close monitoring to assess its long-term structural health.

A dynamic monitoring system based on vibration-threshold triggering has been deployed in 2020 to automatically record events associated with aircraft crossings. The vibration data are used to extract the natural frequencies of the deck from ambient noise and to quantify vibration amplitudes and deflections during aircraft passages. Each event is matched with ADS-B data to identify the aircraft involved and retrieve its operational parameters, particularly MTOW (Maximum Take-Off Weight) and estimated speed. The three measurement indicators – natural frequencies, vibration amplitudes, and deflections – are correlated with temperature and aircraft MTOW to establish empirical relationships between external solicitations and structural responses.

Results obtained over the monitoring period highlight a strong temperature-frequency dependency and clear relationships between strain amplitudes (encompassing both high frequency vibrations and deflections), temperature and aircraft MTOW. These stable correlations demonstrate the value of combining structural instrumentation with open data in SHM applications. They also indicate that the bridge has exhibited no detectable change in its structural condition over the monitoring period.

Shaly rock formations, particularly those rich in expansive clay minerals, pose unique geotechnical challenges for infrastructure development. These formations are susceptible to volumetric swelling and deformation when subject to water ingress, mechanical stress and salt concentration, which can lead to progressive structural damage over time. The long-term swelling effect of shale formation in combination of cyclic thermal and environmental changes induce additional stress on the structure in contact with the shale. This paper illustrates the use of a long-term monitoring program aimed at assessing crack growth and crack propagation of an underground structure situated within shale-dominated geological environments in Southern Ontario, Canada. Real-time continuous data was collected over an extended period to reveal any correlations of seasonal thermal and moisture changes and the deformation of the structure. Furthermore, short-term stress responses were determined based on crane live load tests. These provided insight into the dynamic responses of the structure. The analysis of the time-series data led to the establishment of displacement and strain threshold limits, which ultimately enhanced the structure’s long-term performance and safety. The findings highlight the importance of continuous monitoring in predicting long-term structural responses and support the development of early warning systems and mitigation strategies.