Security and Fragility: The Conservation of a Cultural Asset

Integrated Geospatial and Geotechnical Monitoring Systems

The San Michele bridge, also known as the Paderno bridge, is an iron arch bridge with mixed rail and road traffic. It connects the towns of Paderno d'Adda (LC) and Calusco d'Adda (BG) by crossing a gorge of the Adda river.

Built in 1889, it has been included among the assets protected by the Superintendency for Environmental and Architectural Heritage of the Lombardy Region since 1980, constituting a fundamental stage in the historical evolution of infrastructure in Italy. The bridge has been recognized as a masterpiece and as one of the symbols of Italian industrial archeology. In 2017 the bridge was also a candidate to be included in the UNESCO list of World Heritage Sites.

The Paderno bridge is spread over two levels: with the upper level used for vehicles, while the lower one is reserved for railway traffic. The structure is supported by seven iron piers with two symmetrical parabolic arches forming the span, giving it its iconic appearance.

Extraordinary maintenance work was started in 2021 aimed at restoring the safety standards as prescribed by local regulations. The restoration included the structural reinforcement of the bridge and the complete reconstruction of the roadway.

The Trimble S9 automatic total station.

For this reason it was closed to both road and rail traffic for over a year (see files No. 80 March/April 2010 on p. 84 and No. 139 January/February 2020 on p. 90 with https://www.stradeeautostrade.it/ponti-e-viadotti/il-ponte-san-michele-di-paderno-dadda/).

The contractor collaborated with the Tecno In Geosolutions SpA engineering firm for the necessary geospatial analysis and structural monitoring during the redevelopment phases.

Monitoring with Trimble Solutions to Ensure Infrastructure Security

Structural monitoring is the complex operation of acquiring data, either manually or automatically, of certain structural parameters in order to have real-time information on the behavior of a structure or infrastructure. Integrating static and automatic monitoring is therefore a fundamental tool for verifying real behavior with respect to the design model, updating numerical models, evaluating operating performance and analyzing the structural health. 

In this case, monitoring served the purpose of verifying the general behavior of the infrastructure, and measuring and analyzing the movements of the structural elements of the bridge. This was done to guarantee the safety of the workers working on the bridge during the extraordinary maintenance phase and to ensure the solidity and integrity of the historical infrastructure subjected to stresses deriving from the works.

An integrated monitoring system – including geospatial, geotechnical and automated instruments – was installed to guarantee a complete overview of the bridge. 

Workman carrying out work for the maintenance of the San Michele bridge.

Teams carefully chose measurement sensors developed for intensive use in an open environment, to ensure the continuity and quality of observations. 

A Trimble S9 0.5” model automatic total station was installed at a distance of about 200 m from the structure in a position with wide visibility of the bridge. It measured a total of 78 prisms, four of which were reference prisms installed on structures considered stable positioned near the bridge. The remaining 74 were monitoring prisms installed in correspondence with the structural elements whose behavior is considered significant for control purposes.

The total station was equipped with an electrical panel with IP65 rating. The accessory components necessary for the functioning of the station, such as the communication and power supply system, are housed inside.

The station was powered by a 220V mains and equipped with a buffer battery to guarantee its operation for at least 24 hours following any interruption of the electricity supply. Communication between the total station and the management software on the remote server is accomplished via a UMTS (Universal Mobile Telecommunications Service) router communication device enabling remote access and management of the system.

The hardware and software reproduction of the monitoring system used on the San Michele bridge.

Data acquired from field sensors is automatically imported into the Trimble T4D cloud software platform where it is graphed, displayed and made available for analysis and reporting.

Within the platform, alarm thresholds have also been set on three levels which, when exceeded, enable notifications to be sent via email or text message to stakeholders for awareness. The data is then made available on the platform in graphical and tabular formats in 3D coordinates. They can also be displayed on a map complete with indications regarding the geospatial displacement vectors and displacement speed.

The geodetic monitoring of the bridge was integrated with the installation of 100 micro-strain gauges and 15 tri-axial accelerometers for the analysis of vibrations, loads, frequencies, ranges and tolerances providing additional parameters for understanding the structure health. The system also acquires data from a gateway unit which records the environmental weather data. This data is essential to apply the corrections of the measurements acquired by the other field technologies.

The Software Benefits From Trimble Monitoring

The project required measurements taken at hourly intervals in order to control the effects of the work on the thermal response of the bridge. The system was installed prior to the start of maintenance to obtain a representation of the bridge’s behavior under normal operating conditions. 

This acquisition period was essential to the definition of the system baseline, the definition of the alarm thresholds and the choice of optimal processing settings for the acquired data.

The representative map of the location of the sensors of the monitoring system installed along the San Michele bridge.

The Trimble 4D web interface allowed  the construction team  to access real-time data,, each with their own access level defined according to their role (administrator, analyst or viewer).

Reports were automatically generated, reporting on the system status and movement on-site. The reports were also sent out to key stakeholders automatically as per administrator settings. 

Upon completion of the maintenance, the structure continued to be monitored for a period of time to ensure the normal behavior of the bridge following the reopening to road and rail traffic.

Conclusion

Trimble monitoring systems and software have been developed to meet infrastructure monitoring needs, specifically to guarantee the safety of workers on site by analyzing the behavior of the bridge with respect to the design parameters.

The software represents the heart of a monitoring project: activating alarms based on user-defined thresholds, checking measurements, managing data, as well as compiling and analyzing results in real time. These are all fundamental aspects to be able to recognize risk situations and take any mitigating actions with adequate notice.

The monitoring control station with dashboard, thresholds and alarms.

The Trimble monitoring system provides the ability to collect and analyze measurements from different sensors  to exploit them within a single web platform in the cloud, have a daily report available, and share as needed with project stakeholders.

These features, combined with the advanced alarm functions, make it possible to monitor and evaluate the response of the bridge with respect to the stresses that the maintenance may cause, and provide decision-makers with the information necessary to evaluate any dangerous situations that could require work and traffic stoppages.

Visit Spektra Italy - a Trimble company, providing monitoring solutions to help with the safety of bridges and viaducts.

Link to original article on Strade & Autostrade.