Bridge monitoring systems
Fiber optic system for bridge monitoring
Let's prevent tragic events!
Dozens to hundreds of bridges in the Czech Republic are in poor, if not critical, condition. How is it possible to determine which bridge can still last and which, on the contrary, needs immediate repair? The ideal solution is the implementation of fiber-optic sensors and the measurement of structural stress along with other parameters in real time.
Measurement of existing bridges
The most important measurement on bridges is the determination of the relative strain of the reinforced concrete structure. Using fiber-optic sensors, it is possible to measure changes in length with high frequency and sub-micron resolution, making it possible to evaluate the time-dependent behavior of the bridge and thus detect potential deficiencies or even critical structural conditions.For existing bridges, it is appropriate to carry out these measurements on the surface of the bridge structure using external optical strain gauges, which typically range in length from 0.3 m to 1 m. The specific placement and the required number of sensors are always determined by a specialist designer or structural engineer.
Surface sensors are anchored at a shallow depth and therefore do not compromise the structural integrity of the bridge. In the case of chamber girder bridges, installation is carried out inside the chamber. The most important information about a bridge’s development comes from long-term continuous measurements, which make it possible to assess its condition, predict its future behavior, and determine its maximum permissible load. In the case of reconstruction of existing bridges, surface optical strain gauges are also used to monitor the structure’s behavior throughout the reconstruction process.
Real-time measurement 24/7
Online monitoring provides comprehensive information about the behavior of bridge structures under the influence of traffic and weather conditions.
Measurement of segmental bridges
A special type of structure is represented by bridges from the 1960s and 1970s, which were made of girders composed of post-tensioned precast girders. The vast majority of these bridges have already exceeded half of their intended service life and are often in unsatisfactory technical condition. The causes of critical failures are mainly insufficient protection of the prestressing reinforcement and its anchorage, the absence of grouting, subsequent corrosion, and minimal or even no conventional reinforcement. As a result, the girders effectively become elements of plain concrete prestressed with unbonded tendons and gradually lose their load-bearing capacity due to corrosion. Contributing factors also include a significant increase in traffic over recent decades and neglected maintenance. Only the timely detection of the initial opening of cracks, followed by measurement of crack width, provides the bridge operator with crucial information on whether it is necessary to restrict traffic, reduce the bridge’s maximum permissible load, or even close the bridge altogether. Only continuous online monitoring can prevent further extraordinary events.
We have therefore developed specialized fiber-optic sensors for detecting the initial opening of cracks as well as for subsequently measuring their widening. The sensor detects crack initiation at a width of approximately 100 μm (this threshold can be adjusted depending on the girder length). Since most of these bridges do not have access to electrical power, the evaluation unit is battery-powered and, at a set interval (e.g., twice a day), checks the cracks and transmits data indicating whether an initial crack opening has occurred. The battery life is up to 6 months, and it is possible to monitor up to 32 cracks simultaneously.
First crack opening between segments
A key moment in terms of the bridge's service life. From this point on, the crack opening must be measured continuously.
Measurement of newly constructed bridges
For newly built bridges, optical strain gauges designed for direct embedding in concrete are primarily used. These sensors are installed progressively on the reinforcing steel before the concrete is poured. They are placed in bridge pilons, pilon foundations, and mid-span sections. The number, placement, and measurement range of the sensors are determined by a bridge engineer who can then compare the collected data with simulation models and predict the bridge’s behavior.It is advantageous to monitor the bridge already during construction, especially at highly stressed locations, such as measuring pilons deformation or the deformation of cantilever segments during balanced cantilever construction. The sensors can be gradually connected to a preliminary distribution rack with evaluation electronics, allowing data to be collected already during the construction phase. The evaluation electronics are housed in climate-controlled cabinets, which can be installed inside the bridge chamber, on the bridge surface, or even remotely from the bridge, depending on the client’s requirements and site conditions.
Measurement of dynamic events
In addition to long-term static measurements, it is also advisable to monitor dynamic events that occur on bridges, particularly due to traffic. Using our system, it is possible to measure the amplitude of such events at frequencies of up to 50 kHz, making it possible to assess how these rapid phenomena affect long-term measurements and whether permanent damage to the bridge structure has occurred as a result of a single transient event.
Temperature measurement
For a complete analysis of bridge behavior, it is also important to know the temperature profiles at defined locations, especially for arch bridges. Our fiber-optic strain gauges measure temperature as part of their internal temperature compensation; for additional temperature monitoring, we offer surface-mounted and immersion point sensors, as well as sensors for temperature gradients.The temperature distribution within the structure, together with relative strain, provides a comprehensive picture necessary for assessing the bridge’s condition. The operating range of the temperature sensors is from −30 °C to 70 °C.
We know where and what to measure
A chronic issue in bridge measurement and monitoring is the lack of input from specialized experts in bridge engineering when determining the types, quantities, and placement of measurement points. As a result, monitored bridges are often equipped with various sensors positioned in unsuitable locations and in inappropriate numbers. The outputs of such measurement systems then lack sufficient informational value regarding the behavior and development of the monitored structure. Our systems are always implemented based on an analysis of the specific bridge structure carried out by leading bridge engineering specialists, ensuring the acquisition of sufficient relevant data for a responsible assessment of both the current condition and the expected development of the structure. Before the actual configuration and installation of the sensor system, simulations, calculations, and analyses of the expected behavior of the bridge are performed. Based on these, the sensor system is then designed, assembled, and installed. The system is thus tailored to the monitored structure and provides designers, contractors, and subsequently operators with a comprehensive tool for diagnostic monitoring of all significant phenomena occurring within the bridge structure, in correlation with external influences (e.g., temperature, wind force and direction, traffic intensity). Based on this, the system is able to evaluate non-standard structural behavior and generate warnings and alarms.
Data processing and visualization
The data obtained from measurements is processed by evaluation electronics and sent via an 4G/5G interface to a server, which collects and stores the data using the MQTT protocol over a secure line (TLS/SSL) in SQL database. This is a complete solution for collecting data from evaluation units with automated storage in a database. The data is presented to users in the form of web visualization with a wide range of options, such as trend display or export for further processing. Remote data access to the system allows its integration into commonly used add-on systems and is always secured against unauthorized use. The system allows to set detection levels or data transmission frequency, offers the transmission of information about static and dynamic events, and collects and archives sorted values in a database. The cloud solution provides access to current and historical data via a web interface (also possible in the form of a private cloud on your own servers).
Measurements during load tests
We also offer a system for temporary measurement of chamber, segment, girder and other bridge structures in order to observe the effects of traffic, weather conditions, or load testing. This allows the customer to obtain measurement and data-processing services without the need to purchase the entire system. Sensors are temporarily installed at predefined locations and connected to the evaluation electronics. Through continuous measurement of strain, crack opening, and temperature, it is possible to monitor bridge behavior under various weather conditions, traffic loads, or during load test, and thus verify whether the structure behaves elastically and to what extent it can continue to sustain operational loads. In the case of load testing, the highly accurate surface-mounted FBG strain gauges make it possible to monitor strain changes with sub-micron resolution.
Measurement of non-systemic pilots
Static load tests carried out on non-system piles to verify pile load-bearing capacity under specific geological conditions are often an essential step before the start of bridge construction works. In addition to settlement measurements, these tests typically also include the measurement of pile strain. Fiber-optic FBG strain gauges can continuously measure the relative strain of piles at several height levels under varying loads, thereby enabling assessment of the adequacy of shaft friction acting on the pile. In addition to load testing, it is also possible to measure concrete shrinkage during curing, including temperature monitoring.
Turnkey monitoring system – from design to condition assessment
A combination of bridge construction experts and precision measurement specialists.
- We offer comprehensive solutions from A to Z.
- Individual solutions for every bridge
Our goal is not just to sell components and install them, or to supply row "DATA" that no one understands!
Our goal is to design, implement, and operate a comprehensive monitoring system that can, based on current and historical data:
- provide information about the condition of the bridge structure,
- alert you to the need to address the situation in the event of deterioration or detection of non-standard behavior
We offer complete solutions
- Design
- Project documentation
- Implementation
- Data acquisition
- Data evaluation
- Data archiving
- Service & Maintenance
Additional supplementary measurements of external influences
Traffic data measurement
- traffic intensity
- vehicle speed and direction
- vehicle weight
- vehicle category 8+0 / EUR13
Measurement of meteorological variables
- air temperature, dew point, pressure, wind direction and speed, precipitation...
- temperature and characteristics of the road surface
Camera monitoring
- visual tracking of objects
- matching image data with measured events
- video analytic functions
Advantages of the FBG sensors:
- High sensitivity, accuracy, repeatability, and stability of measurements.
- Long service life of FBG sensors compared to electromechanical sensors.
- Completely passive sensors, no power supply required.
- Resistance to chemically aggressive environments, radiation, low and high temperatures.
- possibility of placing sensors several kilometers away from the evaluation electronics,
- immunity to electromagnetic interference and stray currents,
- continuous real-time measurement
