Sensor Applications in Bridge Monitoring: A Practical Path from Data Acquisition to Safety Early Warning

Structural safety is the core objective in the full life cycle management of bridges. As bridges age, they may experience slow but continuous structural deformation due to factors such as traffic loads, environmental erosion, and geological changes. These changes are often difficult to detect through visual observation or regular inspections, and sensor-based automated monitoring systems are becoming an important technical means to ensure the long-term safe operation of bridges.

Modern bridge monitoring has evolved into a comprehensive, multi-parameter, continuous, and remote system. Its core lies in deploying various sensors to acquire critical structural status information in real time and transforming this data into analyzable and predictable engineering data. Common monitoring parameters include structural tilt, displacement, strain, vibration frequency, and ambient temperature and humidity. Each type of sensor plays a different role in the system.

Tilt sensors are used to monitor changes in the bridge's attitude, such as pier tilt, support offset, or main beam torsion. These changes are usually caused by uneven foundation settlement. In the early stages, the angle change is minimal, but long-term accumulation can affect the structural stress balance. High-precision tilt sensors can resolve angle changes within 0.01 degrees. Combined with temperature compensation algorithms, they can maintain data stability even in environments with large diurnal temperature variations. Installation locations are typically chosen at the top of piers, at the base of towers, or near expansion joints to ensure effective coverage of critical areas.

Displacement monitoring focuses on the relative movement between structural components. For example, the opening and closing of bridge expansion joints fluctuates with temperature changes. Displacement within the normal range is within design expectations, but exceeding limits may indicate support jamming or abnormal beam end constraints. Wire-type displacement gauges or non-contact laser displacement sensors are commonly used in such scenarios, offering high measurement accuracy and long-term stability, making them suitable for long-term outdoor use.

Strain sensors directly reflect the stress state of materials. By attaching or installing strain gauges in stress concentration areas such as the mid-span of the main girder, the bottom of the bridge tower, or the anchorage zone of the stay cables, stress response curves can be recorded during vehicle traffic. Analyzing strain amplitude, cycle count, and residual strain can assess the degree of fatigue damage to the structure and determine if overloading or load-bearing capacity degradation is present. This data has practical guiding significance for developing maintenance plans and traffic restriction strategies.

Vibration sensors are used to capture the dynamic characteristics of bridges. By recording the vibration response of the structure under wind loads, traffic flow, or earthquakes using accelerometers, modal parameters such as natural frequency and damping ratio can be extracted. When cracks, loose connections, or decreased stiffness appear in the structure, its natural frequency typically decreases. Long-term tracking of the trends in these parameters helps identify potential structural problems.

In addition, environmental sensors such as thermometers and hygrometers, while not directly reflecting structural condition, are indispensable for data analysis. Temperature changes cause thermal expansion and contraction of materials, affecting displacement and strain readings; high humidity environments can accelerate steel corrosion. Synchronizing environmental data with structural response data allows for a more accurate distinction between normal fluctuations and abnormal behavior.

All sensors are connected to the data acquisition system via wired or wireless means. Data is filtered, calibrated, and then transmitted to the monitoring platform. The system supports threshold alarms, trend analysis, and report generation, helping maintenance personnel to promptly grasp the bridge's status. Some systems also possess edge computing capabilities, enabling preliminary data processing locally and reducing communication overhead.

In practical applications, sensor reliability directly impacts monitoring effectiveness. Equipment exposed outdoors for extended periods must have IP68 protection rating, a wide operating temperature range (-40℃ to +85℃), and electromagnetic interference resistance. Simultaneously, low-power design supports battery or solar power, suitable for remote bridges without mains power.

An effective monitoring system depends not only on hardware performance but also on installation specifications and subsequent maintenance. Sensor placement should be tailored to the characteristics of the bridge structure to avoid interfering with traffic or affecting aesthetics; data acquisition frequency should be set reasonably according to the monitoring target, taking into account both accuracy and storage cost.