Bridge monitoring
structural diagnosis, monitoring and predictive maintenance of civil engineering structures
France has between 200,000 and 250,000 road bridges, of which nearly 90% are managed by local authorities. According to the Senate report "Bridge Safety: Avoiding a Tragedy", at least 25,000 structures are in poor structural condition and present safety or availability issues for users.
Five years after this report, the findings remain concerning. Evaluations conducted as part of the National Bridge Programme led by Cerema show that many structures require enhanced monitoring. Of more than 63,000 municipal structures recorded, only 28% are considered to be in good condition, while 29% show significant or major structural disorders requiring in-depth studies and subsequent repair work.
In this context, periodic inspections remain essential but do not always allow for understanding the actual evolution of a disorder between two visits.
Monitoring of cracks, inclinations, deformations or vibrations then becomes a valuable tool to complement the structural diagnosis of bridges and guide maintenance decisions.
National Bridge Programme – Cerema
State of municipal bridges in France (Cerema, 2024)
The limits of traditional inspections
Detailed inspections, IQOA visits (Image of the Quality of Engineering Structures) and structural expertise remain essential in the management of engineering structures.
They allow for :
establishing a structural diagnosis ;
identifying the pathologies ;
evaluating the level of risk ;
to prioritise interventions.
However, these inspections only provide a snapshot of the state of the structure at a given moment. Between two inspection campaigns, the actual evolution of a disorder often remains unknown.
Is a crack observed during an inspection truly stabilised or does it continue to evolve over the months? Is a pile rotation temporary or does it indicate a progressive movement of the structure? Are the observed displacements related to foundation settlement, temperature variations between summer and winter, or to stresses induced by traffic?
Only continuous monitoring can answer these questions by distinguishing normal seasonal variations in the behaviour of the structure from movements that may indicate a more concerning disorder.
What parameters to monitor on a bridge?
Crack monitoring
Crack monitoring is one of the most used indicators in the structural diagnosis of bridges. The objective is not only to observe the presence of a crack but to measure its evolution.
A stable crack does not present the same issues as an active crack whose opening progresses over time.
Monitoring of inclinations
Monitoring of inclinations allows for the detection of rotations and tilts affecting :
the piers ;
the abutments ;
the retaining walls ;
the load-bearing elements.
These measurements are particularly relevant for identifying differential settlements or geotechnical movements.
Monitoring of columns and piers
Columns, piers, and supports are critical elements in the behaviour of a structure.
Their monitoring allows for early detection of :
a loss of verticality ;
an abnormal rotation ;
a gradual displacement ;
a local deformation.
Bridge deformation
The analysis of deformations is a central element of the monitoring of civil engineering structures.
It allows for understanding the actual response of the structure to the stresses :
traffic ;
temperature ;
wind ;
ground movements ;
material ageing.
Vibrational monitoring
Vibrations represent a true signature of the structural behaviour of a bridge.
The evolution of natural frequencies or vibrational amplitudes can reveal a change in stiffness or the emergence of structural disorder.
From diagnosis to Structural Health Monitoring (SHM)
For several years, infrastructure managers have been gradually moving towards Structural Health Monitoring (SHM) approaches.
SHM involves continuously monitoring a structure using sensors to gain a detailed understanding of its actual behaviour.
The objective is no longer just to identify a disorder when it appears, but to:
track its evolution;
understand its causes;
validate the engineers' hypotheses;
improve predictive maintenance;
reduce the risks of emergency intervention.
This approach is now widely used on major engineering structures, strategic bridges, and sensitive infrastructures.
FEELBAT solutions for bridge monitoring
To support infrastructure managers, FEELBAT is developing a range of connected sensors dedicated to structural monitoring and infrastructure monitoring.
DELTA L+, DELTA L+mini & DELTA X-L100: crack monitoring
The DELTA L+ allows for the measurement of the evolution of a crack's opening over time.
The DELTA L+mini allows for the measurement of the evolution of a crack's opening over time in correlation with the impact of light.
Le DELTA X-L100 permet de mesurer l'evolution of the opening of a large amplitude crack (100mm) over time.
All connected FEELBAT sensors integrate temperature measurement.
The collected data allows for the identification of acceleration phases, seasonal behaviours, as well as the effects of traffic or thermal variations.
DELTA R: monitoring of inclinations
The DELTA R measures the rotations and angular variations affecting the piles, abutments, columns, or decks.
These measurements allow for monitoring the evolution of the stability of the structure and for early detection of certain structural movements.
FEELBAT inclinometric lines
For structures requiring a global view of their behaviour, several DELTA R can be grouped within an inclinometric line.
This representation allows for visualising deformations, rotations, and relative displacements across the entire structure and quickly identifying the most stressed areas.
A module has been specifically developed to convert degrees directly into mm to facilitate the visualisation of deformation.
DELTA V: vibrational monitoring
The DELTA V allows for monitoring vibrations induced by traffic, environmental conditions, or certain dynamic phenomena.
Frequency analysis is a valuable complement to structural diagnosis and traditional inspections.
Coming soon to the FEELBAT shop
The advantages of FEELBAT monitoring solutions
The FEELBAT sensors have been designed to be plug & play, with a quick installation achievable in just a few minutes on most structures. Without complex wiring or heavy infrastructure, they allow for easy deployment of a monitoring solution on a bridge, a retaining wall or any other structure.
Data is accessible remotely from a web and mobile application, with real-time visualisation, measurement history, automated PDF report generation and management of customisable alert thresholds. In case of abnormal changes in a crack, tilt or vibration, users can be immediately notified by email or SMS.
Thanks to support for multiple communication protocols (Sigfox, LTE-M and 4G), FEELBAT solutions can be deployed in most regions of the world while maintaining autonomy of up to several years.
Conclusion
Bridge monitoring is gradually evolving towards Structural Health Monitoring approaches that go beyond periodic inspections.
Monitoring cracks, tilts, columns, deformations and vibrations provides engineers with essential information to understand the actual behaviour of a structure, optimise maintenance programmes and anticipate interventions before critical issues arise.
In this approach, the connected FEELBAT sensors represent a simple solution to deploy for instrumenting civil engineering works and establishing a genuine predictive maintenance strategy.