Table of Content
- Stages of SHM in INS and Ports
- SHM Approaches for INS and Ports
- Sensors and Sensing Systems
- Classification of INS and Port Facilities
- Factors Affecting Seaport Facilities
- SHM of General Port Structures
- SHM of Coastal Structures
- SHM of Waterway Protection Structures
- SHM of Navigation Locks
- SHM of Accessory Structures
- Value of SHM Systems for INS and Ports
- Key Takeaways
- FAQs
Structural Health Monitoring (SHM) is the assessment and maintenance of the structural integrity of test subjects by continuously monitoring their condition. Parameters such as strain, displacement, and vibrations are inspected by deploying various sensors and analytical tools to track them.
The global SHM market was valued at USD 5.87 billion in 2023 and is projected to grow significantly, reaching approximately USD 27.06 billion by 2034. This growth is driven by increasing awareness of infrastructure safety, advancements in sensor technology, and the need for cost-effective maintenance strategies.
Stages of SHM in INS and Ports
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Ports and their associated infrastructure are vital components of the global economy, facilitating the movement of goods and contributing to international trade. Their functionality directly impacts economic stability and growth. SHM of Inland navigation structures (INS) and ports ensures these critical structures remain operational, safe, and efficient.
Data Collection:
Here, various sensors are deployed to capture real-time data on structural parameters. These sensors measure strain, displacement, temperature, and vibration, providing a view of the structure's condition.
Performance Assessment:
The data is analysed to identify damage-sensitive features and evaluate the structure’s performance and safety. This involves interpreting the data to detect probable issues and assessing the overall health of the structure.
Infrastructure and port facilities can be maintained by implementing effective SHM strategies that mitigate risks and ensure their continued contribution to the global economy.
SHM Approaches for INS and Ports
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SHM uses diverse approaches tailored to specific monitoring needs, each offering unique benefits and challenges in practical applications. These include:
1. Strain-Based Approaches:
Strain correlates with stress and deflection, where abnormal strain indicates potential damage. This approach utilises traditional strain gauges (SGs) and advanced optical sensors. It is effective in global SHM and decision support under increased loads.
2. Displacement-Based Approaches:
This method monitors structural displacements (e.g., settlement, tilt) as indicators. LVDTs, LiDARs, InSARs for capturing static and dynamic displacements. It monitors geotechnical phenomena and hard-to-visualise deformations.
3. Vibration-Based Approaches:
Vibration characteristics reflect structural condition changes. This method uses accelerometers and FBG-based sensors for multipoint measurements. Frequency domain methods (OMA) assess modal properties during regular operations.
Physics-Based vs. Data-Driven Approaches:
- Physics-Based: This uses FE models to simulate structural behaviour, requiring extensive data and computation.
- Data-driven: It relies on machine learning and historical data, offering real-time insights with minimal structural knowledge.
The SHM approach directly influences the selection and deployment of sensors and sensing systems.
Sensors and Sensing Systems
Sensors, along with emerging technologies in remote sensing, enhance the accuracy and effectiveness of SHM. Sensors can be classified as follows:
A. Contact Sensors
1. Displacement Sensors:
- Linear Variable Differential Transformers (LVDTs)
- Crack Meters
- Vibrating Wire Sensors
- Multi-Point Bore-Hole Extensometers (MPBXs)
- Eddy Current Sensors
2. Strain Gauges (SGs):
- Traditional SGs
- Vibrating Wire SGs (VWSGs)
3. Accelerometers
4. Inclinometers/Tiltmeters
5. Load Cells
6. Pressure Sensors
7. Fiber Optic Sensors (FOSs)
8. Temperature, Humidity, and Corrosion Sensors
B. Non-Contact Sensors
1. Computer Vision (CV)
2. Synthetic Aperture Radar (SAR)
3. Sonar:
- Echo Sounding
- Side-Scan Sonar
4. Geophysical Methods:
- Electrical Resistivity Tomography (ERT)
- Ground-Penetrating Radar (GPR)
C. Remote Sensing
1. Interferometric SAR (InSAR)
2. Global Positioning System (GPS)
Recent advancements in remote sensing and satellite-based techniques like InSAR enhance the accuracy of SHM for large and complex structures. These technologies promise improved monitoring and data analysis capabilities for civil infrastructure.
Classification of INS and Port Facilities
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Port facilities consist of various components that ensure the structural integrity and functionality of the infrastructure. It is imperative to understand the classification of these components and the primary stressors affecting them. The components of seaport facilities include:
- Tetrapod Concrete Armor
- Quay Wall
- Harbor Piers
- Wharf
- Rock Armor Revetment
- Rubble Breakwater
- Sheet Pile Wall
- Caisson Breakwater
- Stressors Leading to Structural Deterioration
INS and Port Facilities are classified as follows:
- General Port Structures
- Structures Extending Out from the Shore: Caissons and Piers
- Coastal Structures
- Structures Parallel to the Shore: Port Wharves and Quays
- Waterway Protection Structures
- Groynes and River Banks
- Dikes
- Navigation Locks
- Lock Gates
- Local Monitoring
- Global Monitoring
- Accessory Structures
- Storm Surge Barriers
- Navigable Aqueducts (Bridges for Waterways)
- Ship Lifts (Lift Locks)
Image Credit: Wikipedia
We can classify the applicability of different NDT methods, as they prove effective in the SHM of such structures, as follows:
Factors Affecting Seaport Facilities
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Maintaining the structural integrity of port facilities is a complex task that requires careful consideration of the components and the stressors that affect them. It is possible to achieve comprehensive monitoring and early detection of issues using NDT methods. The factors affecting seaport facilities include:
1. Scouring:
Sediment removal around foundations which leads to potential instability.
2. Sulphate Attack:
Chemical degradation of concrete components due to exposure to sulphate-rich environments.
3. Corrosion:
Degradation of steel reinforcements and other metallic components caused by the extreme marine environment.
4. Wave Action:
Continuous wave impact leads to mechanical wear and erosion of coastal and harbour structures.
5. Ship Impacts:
Physical damage due to accidental collisions or berthing operations.
These stressors can result in both global and local changes in foundation structures. Global changes, such as uneven settlement, overturning, and sliding, often manifest as visible cracks or heaving on deck surfaces. Local changes, such as scouring at the foundation structure interface, require more detailed monitoring.
SHM of General port structures
General port structures, including concrete, steel, and geotechnical components, require specialised inspection and monitoring techniques due to their exposure to marine environments and the complexities of port operations.
- Environmental Stressors: Marine conditions lead to corrosion, thermal errors, and short circuits in conventional electrical sensors. Water levels fluctuate, affecting the natural frequency and damping ratios of structures.
- Design and Structural Issues: Inconsistencies in prior designs may require targeted retrofitting measures. Post-extreme event damage necessitates special investigations to identify structural flaws.
Methods for Monitoring General Port Structures:
1. Conventional Displacement Measuring Techniques:
Contact sensors are limited by single-location measurements, which are not ideal for comprehensive monitoring. Accessibility issues may also arise in submerged locations, such as caissons.
2. Vision-Based Monitoring:
This is effective for monitoring 6-DOF displacements (slope, deflection, slip) at multiple points, and it extends beyond infrastructure to monitor ship berthing.
3. Vibration-Based SHM:
This monitors vibrational parameters to assess structural conditions. It requires adjustments for water level fluctuations that alter natural frequency and damping.
Structural Health Monitoring (SHM) of general port structures demands tailored approaches due to the challenges posed by marine environments and the complex nature of these infrastructures. To understand the structural health of general port structures we can separate these structures into two groups: structures parallel to and extending out from the shore.
SHM of Structures extending out from the shore: Caissons and piers
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Structures extending out from the shore, such as caissons and piers, are vulnerable to soil-structure interactions and environmental stressors. Damage at the soil-structure interface, including scouring and slippage, can lead to significant issues such as tilting, displacement, and settlement, especially during seismic events.
The factors affecting Caissons and Piers include:
- Soil-Structure Interaction: Slippage at the soil-structure interface is a primary source of damage. Seismic activity can cause significant displacement, rotation, and settlement.
- Environmental Stressors: Wave actions and scouring are key contributors to structural deterioration. Temperature fluctuations impact the stability of quay walls during dredging activities.
Methods for Monitoring Caissons and Piers include:
1. Vibration-Based SHM:
Modal Strain Energy (MSE): Highly sensitive to damage, particularly effective for interconnected caissons.
Dynamic centrifuge tests and harmony search methods: Utilised to monitor foundation-level damage.
Vibration monitoring is sensitive to water level fluctuations, requiring corrections for accurate damage detection.
2. Fiber-Optic Deformation Sensors:
These monitor strains and displacements in quay walls and piles, particularly during dredging activities. It is effective in correlating environmental stressors like temperature with structural stability.
3. Wireless Sensor Systems:
These monitor natural excitation through waves and wind, aiding in damage assessment without forced excitations.
Caissons and piers demand specialised monitoring techniques for complex soil-structure interactions and environmental stressors.
Structures parallel to the shore: Port wharves and quays
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Port wharves and quays are susceptible to deterioration, including settlement, displacement, and structural damage, as they are subjected to harsh marine environments and significant load-bearing stresses. The factors affecting port Wharves and Quays include:
1. Load-Bearing Stresses:
Piled wharves are particularly vulnerable to permanent tilting or settlement due to the load they bear on the soft soils. Dynamic loading during construction and operation can strain the structural integrity of piles.
2. Environmental Stressors:
Seismic activity and liquefaction pose significant risks, as experienced in the 2010 Haiti earthquake, which caused major displacements at the Port-au-Prince wharf. Water level fluctuations and marine conditions accelerate deterioration, particularly in quays along canals. The methods used in monitoring port wharves and quays include:
1. Fibre Bragg Grating (FBG) Sensors:
Strain and Temperature Monitoring: Used extensively in marine environments due to their resistance to electromagnetic noise, moisture, and radio interference.
- Dynamic Strain Measurement: Effective in monitoring strain during pile driving in high-piled wharves, as demonstrated in the Tianjin Port, China.
- Ground Anchor Force Monitoring: FBG sensors serve as stable load cells for long-term monitoring of quay wall stability.
2. Fibre Optic Sensors (FOS):
- Disruption Monitoring: Applied at the Port of Genoa, Italy, to monitor quay wall stability during dredging activities.
- Tie-Rod Monitoring: Used in long-term studies to understand the in-service behaviour of quays, with sensors configured to measure only longitudinal strains.
3. Geophone-Based Surface Wave Monitoring:
- Groundwater Condition Assessment: Efficient in identifying groundwater conditions near sheet pile quay walls, although limited by cost and practicality for long sections.
4. Remote Operated Underwater Vehicles (ROUV):
- Visual and Sensor-Based Inspections: ROUVs equipped with cameras and sensors offer a safer alternative to human divers for monitoring underwater sections of quays.
5. Satellite-Based InSAR Monitoring:
- Displacement Measurement: InSAR techniques have shown promise in detecting structural deformations along quays, with improved accuracy when calibrated with ground observations.
Monitoring port wharves and quays involves a combination of advanced sensing technologies to detect and assess structural health.
SHM of Coastal structures
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Coastal structures such as breakwaters and revetments protect shorelines from wave action and other marine forces. Due to their exposure to harsh conditions, these structures are prone to various forms of damage, including shifting between interlocking blocks and structural failure.
Factors affecting coastal structures:
1. Wave Action:
Long-wave action can cause armour layers to shift, exposing the inner core to more damage. Storms and tsunamis significantly impact the stability of these structures.
2. Structural Integrity:
Sliding of the superstructure, overtopping, toe instability, and excessive settlement are common failure modes. Scouring at the foundation level leads to displacement and settlement issues.
Methods used to monitor coastal structures:
1. Vibration-Based SHM:
These measure forces and accelerations caused by waves, aiding in the assessment of structural stability. Useful in evaluating the impact of storms and docking vessels on breakwaters.
2. Image-Based Monitoring:
This includes aerial photographic surveys (using UAVs) and underwater inspections: This helps identify breakages in armour protection but is time-consuming.
3. Image Analysis:
It detects the displacement of rock blocks in rubble-mound breakwaters, though its field application remains challenging.
4. Visual Inspection and Line Survey
Coastal structures like breakwaters and revetments require robust monitoring systems to withstand the harsh marine environment.
SHM of Waterway Protection Structures
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Navigation waterways require regulation through dikes, groynes, revetments, quays, and locks to maintain navigability by ensuring sufficient width, depth, and controlled currents. These structures also protect residential areas from floods and prevent bank erosion caused by ship-generated waves.
1. Groynes and River Banks:
Groynes are geotechnical structures designed to deflect river flow away from vulnerable zones. They are made from stones, gravel, or soil and exposed to high currents during floods and ship wakes. Monitoring techniques include:
- GIS and Remote Sensing
- TLS and LiDAR
- CV-based Systems
2. Dikes:
Dikes protect against floods, and their monitoring is crucial for assessing structural stability. Monitoring methods include:
- Soil Parameter Monitoring
- AI and Early Warning Systems
- Geophysical and Remote Sensing Techniques
Long dikes (e.g., 17,000 km in the Dutch flood defence system) are challenging to monitor. Remote sensing techniques like LiDAR and InSAR provide critical data for immediate interventions and are essential, especially in unsafe conditions. Advances in UAV-mounted sensors and AI systems promise to enhance the effectiveness and efficiency of monitoring waterway protection structures.
Image Credit: Flickr
Navigation locks enable vessels to traverse water bodies with varying levels by raising or lowering water within a lock chamber using movable gates and control valves. Navigation lock gates can be classified based on the hydraulic load transfer mechanism. The three most prevalent types are:
- Miter Gates
- Vertical Lift Gates
- Rolling Gates
These structures are critical for maintaining efficient and safe inland waterways but are susceptible to deterioration and damage. The common damages and issues encountered include:
1. Structural Wear and Tear:
- Gates: Prone to fatigue cracking, corrosion, misalignment, and mechanical failures.
- Lock Chambers and Walls: Subject to scouring, erosion, and material degradation due to water turbulence and vessel movements.
2. Scouring:
Caused by turbulent water flow during lock operations and vessel movements, leading to erosion beneath approach channels and foundations.
3. Operational Failures:
Malfunctions due to mechanical issues, human errors, and environmental factors can result in temporary closures and significant economic impacts.
The monitoring Techniques for Navigation Locks include:
1. Local Monitoring:
- Visual Inspections: The challenges in using VI include the need for dewatering and limited effectiveness in detecting underwater or incipient damages.
- Underwater Inspections: These are conducted by skilled divers or using remotely operated vehicles (ROVs). They use Acoustic Cameras (Sonars) that work in turbid waters for detecting cracks, corrosion, biological growth, and sediment deposition without dewatering.
- Sensor-Based Monitoring:
I. Strain Gauges
II. Growth Meters and Extensometers: These detect structural expansions due to phenomena like alkali-aggregate reactions in concrete components.
2. Global Monitoring:
- Structural Health Monitoring (SHM) Systems:
I. Strain Measurements
II. Laser Scanning
III. Computer Vision (CV)
IV. Accelerometers
- Predictive Modeling
I. Markov Chain Models
II. Artificial Intelligence
Integrating modern sensor systems, predictive models, and remote monitoring techniques can improve early damage detection, reduce operational disruptions, and extend the service life of these essential infrastructure components.
SHM of Accessory Structures
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Accessory structures facilitate navigation and protect waterways from floods in inland waterway networks. These structures include surge barriers, navigable aqueducts, and ship lifts. Although these structures are not as prevalent as dams or locks, their importance necessitates robust Structural Health Monitoring (SHM) systems to ensure their functionality and safety.
1. Storm Surge Barriers:
Surge barriers, or flood barriers, are constructed at the mouths of rivers or tidal inlets to prevent storm surges or tides from flooding protected areas. They safeguard ports and coastal cities from flooding when sea levels rise.
Due to rising sea levels and frequent storms, barriers like the Maeslantkering are closed more often than anticipated. This increases the likelihood of operational failures and the need for regular SHM.
The Maeslantkering has sensor systems that monitor the hydraulic system and structural stresses. Data is collected quarterly and after each annual test closure. This monitoring has allowed the postponement of major maintenance, reducing costs significantly.
Operational since 1982, the Thames Barrier is monitored by a system installed by Monitran, UK. This includes sensors for displacement, pressure, inclination, and vibration.
2. Navigable Aqueducts:
Image Credit: Wikimedia
Navigable aqueducts, or water bridges, carry waterway traffic over obstacles such as valleys, rivers, or other waterways. They are essential for maintaining continuous navigation routes.
The Magdeburg Water Bridge, the longest navigable aqueduct in the world, has been operational since 2003. Its SHM includes monitoring the settlement of piers, temperature changes in the steel structure, forces in bearings, and anchor systems. Geodetic monitoring and accelerometers are used to assess dynamic behaviour and stability.
Major stressors in aqueducts include changes in water level and temperature, which can lead to structural deformations.
Image Credit: Flickr
3. Ship Lifts:
Ship lifts, or lift locks, are mechanical structures designed to raise and lower vessels between water bodies at different elevations. They replace multistage locks in regions with significant elevation differences, reducing passage time by 3–5 times.
Notable ship lifts include the Three Gorges Ship Lift (China), the Niederfinow Boat Lift (Germany), and the Strépy-Thieu Boat Lift (Belgium).
Ship lifts use electromechanical systems, including counterweights, winches, and electric motors. Regular monitoring prevents operational failures and ensures structural integrity, especially in seismically active regions.
Ship lifts in harsh environments or near large dams are subject to additional stressors, such as vibrations from spillways during floods.
Accessory structures such as surge barriers, navigable aqueducts, and ship lifts require continuous monitoring and regular maintenance to ensure long-term safety and functionality.
Image Credit: Flickr
Value of SHM systems for INS and ports
SHM comes with many merits, some of which include:
1. Enhanced Condition Assessment:
SHM systems provide precise structural data, especially in inaccessible areas, complementing periodic visual inspections that offer qualitative assessments.
2. Safe Operations:
SHM monitors the impact of larger vessels and operational conditions, aiding in policy decisions for vessel usage and infrastructure impact.
3. Facility Expansion Monitoring:
SHM tracks structural changes during expansions, including excavation and water diversion effects, ensuring safe construction and operations.
4. Post-Event Assessment:
SHM offers detailed insights after adverse events (e.g., floods, storms), critical when areas become inaccessible for traditional inspections.
5. Monitoring Repairs and Retrofitting:
SHM evaluates the effectiveness of repairs and optimises maintenance by providing quantitative performance data.
6. Service Life Extension:
SHM supports decisions on extending a structure's use beyond its design life and aids in planning for replacement or repairs.
7. Reducing Downtime Costs:
SHM minimises direct repair costs and indirect losses from freight delays and cascading effects by preventing sudden breakdowns.
Image Credit: Flickr
Key Takeaways
- Structural Health Monitoring of inland navigation structures and ports employs various approaches such as strain-based, displacement-based, and vibration-based methods. Each approach offers unique advantages and is tailored to specific structural monitoring needs.
- The integration of advanced sensor technologies, including contact sensors like strain gauges and non-contact methods such as LiDAR and InSAR, enhances the precision and efficiency of SHM. These technologies are critical for detecting and assessing structural health across diverse environments.
- INS and port facilities are classified into port structures, navigation locks, and coastal structures. Non-destructive testing methods like ultrasonic testing and ground-penetrating RADAR are essential for evaluating the condition of these structures and ensuring their longevity.
FAQs
1. What methods are primarily used in Structural Health Monitoring (SHM) of port structures?
A: The primary methods include strain-based approaches using traditional strain gauges and fiber optic sensors, displacement-based techniques like LiDAR and InSAR, and vibration-based methods employing accelerometers. Each method provides valuable data for assessing structural health and integrity.
2. How does sensor technology impact the monitoring of inland navigation structures?
A: Advancements in sensor technology, such as sensitive, receptive and versatile sensors like fiber optic sensors and remote sensing techniques (e.g., LiDAR and SAR), improve the accuracy and efficiency of monitoring. These technologies allow for real-time data collection and more precise assessment of structural conditions, leading to better maintenance and risk management.
References
Prateek Negi, R. K. (2024). Structural health monitoring of inland navigation structures and ports: a review on developments and challenges. Structural Health Monitoring, 23(1):605-645. doi
Precedence Research. (2024, July). Precedence Research. Retrieved from Precedence Research
