Structural Health Monitoring of Highway Bridges for Early Infrastructure Deterioration Detection

Executive Summary

Highway bridges are among the most valuable assets a transport network owns, and most of them are still managed on periodic inspection, which reports their condition on the day of the visit and little else. As traffic grows and the structures age, owners need to know how a bridge behaves under the loads it actually carries.

Structural Health Monitoring (SHM) covers that gap with field sensors, automated data acquisition, and analytics that report structural behaviour continuously. Instead of waiting for the next scheduled inspection, engineers see small changes as they emerge and plan maintenance against measured performance.

This case study covers an SHM system Sentra installed on a major highway bridge, what the first year of data showed, and how it moved the asset owner off reactive maintenance and onto condition-based maintenance.

Project Background

The structure is a four-lane reinforced concrete highway bridge that has carried a major transport corridor for more than three decades. About 55,000 vehicles cross it each day, a large share of them heavy freight, which puts continuous dynamic loading on it well beyond what the original design anticipated.

Routine inspections had consistently classified the bridge as structurally sound, with only minor weathering and localised surface deterioration. Each of those inspections was a snapshot. None of them said anything about how the structure responded between visits as traffic patterns shifted, weather changed, or the material aged.

So the owner went looking for continuous monitoring to fill those gaps. The brief was a reliable performance baseline to measure against, better long-term visibility of the structure, and maintenance planning grounded in measured behaviour rather than in assumption.

Challenges of Monitoring Ageing Highway Bridges

Visual inspection finds what is visible: cracks, corrosion, surface deterioration. It cannot track structural response, and it cannot pick up the gradual changes that only show themselves as a trend across many readings.

Several factors increased the need for continuous monitoring:

• Higher freight volumes and heavier axle loads put millions of additional loading cycles through the bridge every year.
• Seasonal temperature swings, rainfall, humidity, and water ingress all drive concrete deterioration, reinforcement corrosion, and material fatigue.
• After more than thirty years of service, creep, shrinkage, and fatigue begin to change how the structure behaves.
• Fixed inspection schedules force conservative decisions. With limited performance data an owner either intervenes when nothing needed doing, or waits too long.

What the owner needed was continuous structural data, early warning of deterioration, and enough of a record to plan maintenance across the bridge’s remaining service life.

Objectives of the Structural Monitoring Project

The project set out to put continuous visibility on the bridge’s structural performance. The objectives were to:

• Establish continuous monitoring of critical structural components
• Measure structural response under operational traffic loads
• Capture performance data between routine inspection cycles
• Detect early indicators of infrastructure deterioration
• Support condition-based and predictive maintenance
• Improve engineering decision-making using real-time structural data
• Extend asset lifespan while maintaining safety and operational reliability

Structural Health Monitoring Solution Overview

Sentra deployed an integrated Structural Health Monitoring system: field sensors, automated data acquisition, cloud connectivity, and engineering analytics running on one platform.

The system measures the bridge’s response to operational loads and weather without stopping. Readings are collected, processed, and pushed to a central dashboard, so engineers can assess asset performance in near real time.

Comparing current behaviour against the baseline is what separates ordinary operational movement from an abnormal response. Alert thresholds sit on top of that. When a monitored parameter crosses a predefined engineering limit, someone is notified and can investigate while the issue is still small.

The same record feeds maintenance planning, lifecycle forecasting, rehabilitation priorities, and any future engineering assessment of the structure.

Technologies Used

The system uses several sensing technologies to capture engineering parameters across the structure.

Sensor Type	Function
Strain Sensors	Measure stress variation in the primary structural members, which shows load distribution and any unusual stress concentration
Tilt Sensors	Track small angular movements in the piers and supports, the earliest available sign of settlement or displacement
Displacement Sensors	Measure vertical and horizontal movement under operational loading, tracked over the long term
Environmental Sensors	Record temperature, humidity, and other climatic conditions, so environmental effects can be told apart from structural anomalies

Every device runs into a data logger that collects readings and sends them to a secure cloud platform. Engineers work from dashboards showing live sensor data, historical trends, environmental conditions, and any open alerts.

Implementation Phases

The installation ran in four phases, structured to get accurate data while keeping disruption to bridge operations to a minimum.

Phase 1: Structural Assessment

Sentra’s engineers reviewed the existing design drawings, historical inspection reports, traffic data, environmental conditions, and maintenance records to work out which structural components needed continuous monitoring. That review set the baseline for sensor placement and system configuration.

Phase 2: Sensor Deployment

Sensors went onto the primary girders, piers, bearings, expansion joints, and the deck sections carrying the highest operational loads. Each one was calibrated and validated on site so it would hold its accuracy in field conditions.

Phase 3: System Integration

The devices were connected to the central platform through data loggers and secure communication links. Dashboards, automated alerts, and performance thresholds were configured from the design criteria and the expected structural behaviour.

Phase 4: Continuous Monitoring

After commissioning, monitoring ran 24/7. Engineers had unbroken visibility of bridge performance across changing traffic and environmental conditions, on a framework that scales to further structures as the owner adds them.

Results from Continuous Structural Monitoring

The first year produced a full dataset on how the bridge behaves under real operating conditions: a record of structural performance through the daily traffic cycle and across the seasons, rather than a handful of isolated observations.

Traffic Load Performance

The bridge responded predictably to normal traffic and stayed within its design limits. Monitoring did show that certain girders carry consistently higher strain during peak freight movement. Those values sit within acceptable engineering thresholds, but they are the clearest measure available of what growing commercial traffic is doing to the structure, and they go straight into maintenance planning.

Environmental Behaviour

Environmental conditions correlate clearly with structural movement. Temperature swings produced the expected thermal expansion and contraction, and prolonged rainfall changed bearing behaviour and support movement. Reading the structural and environmental data together is what lets engineers separate ordinary seasonal behaviour from a real concern.

Long-Term Performance Trends

Overall structural performance held stable. Some components did show gradual variation in strain and displacement. None of it is an immediate safety risk, but it is the early signature of deterioration, and those components stay under observation.

Engineering Evaluation of Bridge Performance

What continuous monitoring really buys is evidence in place of assumption.

Instead of relying solely on periodic inspection reports, engineers gained access to continuous performance data that allowed them to:

• Evaluate actual structural behaviour under operational loading
• Compare measured performance against original design assumptions
• Assess the impact of increasing freight traffic on critical structural elements
• Quantify the effects of temperature and environmental conditions
• Identify gradual performance changes before visible deterioration occurred

Maintenance is then prioritised on measured condition rather than on the inspection calendar. Resources go to the components that are actually changing, which also cuts the interventions that were never needed.

The historical database the system has built is now the reference point for future inspections, rehabilitation projects, and lifecycle assessments.

Impact of Structural Health Monitoring Solutions

The system changed how the owner runs the asset in several concrete ways.

• Subtle structural changes are identified before they become visible defects or expensive repairs.
• Maintenance planning, rehabilitation priorities, and lifecycle management now run on objective structural data instead of engineering judgement alone. Explore how asset monitoring and facility management changes infrastructure oversight.
• Work is scheduled against actual asset condition rather than a predetermined inspection interval, which removes maintenance that was not needed and improves reliability.
• Budgets and engineering time go where the measurements say they are worth spending.
• Automated alerts trigger investigation as soon as a monitored parameter crosses its threshold, and the bridge stays open while that happens.
• Intervening early reduces long-term deterioration risk, which extends operational life and improves the return on what was originally invested in the structure.

Conclusion

Periodic inspection on its own is not enough to manage a bridge. Traffic patterns, weather, and material ageing all act on the structure between inspection cycles, and all of them change how it performs.

Continuous monitoring closes that gap. Sensing plus analytics gives owners what they need to catch deterioration earlier, plan maintenance better, and keep lifecycle cost under control. See how similar monitoring principles were applied in our IoT Bridge Monitoring on Railway Bridges case study.

Transport infrastructure keeps ageing and the demand on it keeps rising, which is why continuous asset monitoring is moving from optional to standard practice.

Related Resources

Explore Sentra’s related products, solutions, and case studies:

• Structural Health Monitoring Solutions: our full SHM service offering
• Strain Gauges: high-precision strain measurement sensors
• Tiltmeters: angular displacement monitoring devices
• IoT Bridge Monitoring on Railway Bridges: a related case study
• Asset Monitoring & Facility Management: a blog on end to end IoT implementation