Bridge rehabilitation: Monitoring a 40-year-old bridge in real-time before renovation

Author: T/F/D

The Edgar Cardoso bridge in Figueira da Foz, Portugal, is named after the famous civil engineer and professor of bridge construction. Cardoso was a pioneer of the experimental analysis of structures and developed his own high-precision measurement instruments. André Melrinho, Engineer Surveyor from Infraestruturas de Portugal (IP), believes that Cardoso would approve of the new technology used to monitor the bridge before its latest refurbishment. Melrinho and his team used Leica Geosystems monitoring solutions to collect and process data to show its structural behaviour. Maintenance plans for the bridge were prepared based on the results obtained, ensuring that it meets current safety standards and continues to support travellers across the Mondego river.

IP is a state-owned organisation that manages transport infrastructure in Portugal. Its purpose is to plan, design, construct, maintain and operate the national road and railway networks and rehabilitate, extend and modernise them when necessary. The Edgar Cardoso Bridge – 1421 m long, including a cable-stayed bridge and two approach viaducts – was completed in 1982. It is subject to regular maintenance. During the latest evaluation of the bridge, IP assumed the monitoring project to support and prepare recommendations for structural work. According to the IP surveying team, “measurements were essential to define the structural behaviour, and plan a proper and more efficient maintenance intervention.”

Choosing precise tools for measurement

A bridge is an ever-changing structure that poses unique challenges for engineering surveyors. Equipment needs to be precise and sensitive, yet robust and weather-proof. Having used Leica Geosystems equipment on a previous similar project, the team chose a Leica Nova TM50i total station and 44 GPR112 reflectors; a meteorological sensor to monitor temperature and atmospheric pressure; and GeoMoS Monitor, GeoMoS Analyzer and GeoMoS Now! software for data processing and analysis. The total station measurements are used to quantify the bridge's movements with millimetre precision. Accurate information is crucial to this project, and the volume and accuracy of the displacements resulting from the solution were a determining factor for choosing the technology.

Forming structural predictions from comprehensive data

The IP team says that the data collected during monitoring is critical, “allowing [us] to understand the bridge's behaviour at each step consistently.” They explain some of the comprehensive measurements taken: “The TM50i collects horizontal, vertical angles and distances, properly corrected from the atmospheric effects and given displacements after processing all observations. The objective is to evaluate the structure displacements”. The team needed to measure over an extended period to see how the bridge responded to different conditions, to “better define [the] structure’s behaviour when it’s under external factors, such as heavy traffic loads, severe atmospheric conditions, etc..” Being a cable-stayed construction, the behaviour of the bridge towers is of critical importance. “The vertical component will have a very relevant impact since more significant fluctuations in this component are expected.”

In addition to the movement data, meteorological information from the weather sensor was gathered and processed by the Leica GeoMoS software. Graphics and reports were generated by the GeoMoS Now! web application which the team used to communicate results to other IP colleagues.

Remote information and assistance

With numerous solutions for remote access, it is easy to access the Leica solution, check, modify, or adjust the processing and download the data from the database created by Leica Geosystems. The total station performs continuous measurements, which were automatically processed via GeoMoS Monitor and GeoMoS Analyser. Results were made available round the clock via GeoMoS Analyzer and GeoMoS Now! web-based application. Once set up, the team could monitor the bridge without needing to be on-site, saving considerable time. The IP team said that the system was “precise, continuous and automatically remotely accessible.”

The IP team also received fast remote assistance from the Leica Geosystems support team for a firewall issue. “It was necessary for a specialist Leica Geosystems technician to access IP services, from offices in Switzerland, to identify and resolve a firewall conflict. Everything went very efficiently, and in a few minutes, a solution was found.” The team was also pleased with the training, which made sure they used the system to its fullest potential. “We promoted joint training sessions with the Leica Geosystems team and conducted internal training sessions, an ongoing process. The initial learning process was very accelerated; [we] achieved the automation of the process in less [than] 3 to 4 days.”

Trusted partner and technology

When working on infrastructure, it is essential to trust your instruments. Following the successful completion of the monitoring, the surveying team at IP will use the Leica Geosystems solution on their next projects. They say, “the equipment, processes, and other accessories show great robustness and reliability. Due to the system's ease of integrating the various components and time saving, we expect to replicate this solution soon, namely in road and rail infrastructures.”

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