Structural Health Monitoring Flashcards
Infrastructure is the combination of fundamental systems that supports our society.
Why is infrastructure vulnerable?
- Ageing and decay of the infrastructure
- Short term hazards (e.g. natural disasters, accidental damage, terrorist attack)
- Long term change (e.g. climate change)
- Vulnerability from the interdependence of infrastructure networks (failure in one area can spread to others)
What does modern infrastructure need to be?
- Optimised in terms of efficiency, cost, carbon footprint, service quality, aesthetics
- Resilient, robust and adaptable
- Innovative
What is SHM an important part of, and where is it mainly applied to in the civil field?
It is an important part of asset management:
- important to regularly check health condition of assets
- the better condition of the structure, the longer its life is and the better its value
SHM is mainly applied to bridges, retaining walls, tunnels, dams
Define SHM and its role
An activity where actual data related to civil infrastructure is observed, measured and registered
Role:
- to manage risks associated with an asset (current and how it might develop over time)
- predict when zero spare capacity will be reached
“SHM can be used to identify what need to be monitored and how to monitor them, gather the data efficiently and carry out enough analysis to inform decisions”
Understanding the way in which infrastructure changes gives info about the current conditions AND can be used to predict the capacity + performance of the asset throughout its lifetime
What are the three different monitoring techniques for SHM of civil infrastructure?
Visual Inspection (VI):
- what can be seen (optical)
- mostly qualitative
Periodic visit-based monitoring (PVM):
- using instrumentation to test key factors
- detailed quantitative, but ‘snapshot’
Continuous sensor-based SHM (CS-SHM):
- fixed sensors continuously monitoring over defined period
- possible to identify detail, observe changes, identify patterns and trends
NB. In general, PVM and CS-SHM are used in combination with VI
What are limitations of visual inspection
- Physical constraints (access, time, type of data)
- No info on hidden details
- Subjective judgement and lack of clear quantification
When is periodic visit-based monitoring (SHM) used, and when is it effective?
Often introduced following recommendations from a VI
Effective when used to improve knowledge + understanding of some particular identified issue
What are the benefits of continuous sensor-based SHM (CS-SHM)?
- Gather high quality quantitative info in real time
- Can measure a series of events at a high frequency
- Reduce reliance on the need to visit
NB. it is important the owner and user know the purpose of the SHM system, and have a modelling proposal in place
What should be considered in the design of a CS-SHM system?
Some degree of redundancy
E.g. account for the potential loss/defect in one sensor or connection
What is the difference between structural health and structural health monitoring?
Structural health is the foundation of capacity and performance:
- structure has macroscopic (how elements are connected, their integrity + properties) and microscopic (materials, their integrity + properties) levels
- capacity and performance of asset depends on health of structure
Structural health monitoring is throughout the asset’s life:
- health of every asset must be known (quantitatively + qualitatively) for confidence that it is safe for use in the past, present, future
- structural health of all parts of an asset (including hidden) must be measured from the start, with changes monitored throughout the asset’s life
Describe the components of the physical state of an asset, relevant to the function of SHM
Inner ring:
- integrity of materials and the structure of the asset
Middle rings:
- relationship of the load capacity and performance
- provided capacity should exceed required capacity, with a surplus (which allows for deterioration over time)
Outer ring:
- time
- over time the materials will deteriorate/change
- rate of change is important to understand the deterioration
Name different ways in which a structure/materials may deteriorate over time?
- Long-term creep
- Changes in loading (causing overstressing of structural elements)
- Corrosion; can be accelerated by use of de-icing salt
- Delamination
- Large strain, or residual deformation
- Failure of cables
- Unexpected crowd loading, creating torsional response of deck
- Resonance
- Scour (removal of elements by action of water)
- Buckling
- Cracking
- Loss of tendons
- Damage at the joints
Describe a capacity/time graph for a SHM design example, including where the zero spare capacity intervention point is reached
E.g. delamination and cracking of RC before spalling and loss of section
More realistic scenario: gradient of provided capacity gets steeper over time whilst required capacity has different gradients (representing changing conditions); asset at risk earlier
At what point on this capacity/time graph for SHM has the asset been strengthened through intervention?
The asset has been strengthened at T_4
The extra provided capacity extends the asset life
Other than increasing the provided capacity, what is another way in which asset life can be extended
The required capacity can be reduced by restricting the live load in the asset
What SHM was applied to the Clifton Suspension Bridge, and why?
- There were concerns that on one tower the saddles were moving less than expected, due to excessive loading
- SHM system using displacement transducers and temperature sensors was installed in 2000s; had issues (including sensors giving ‘noisy’ results)
- New SHM system installed in 2013, informing simple maintenance (cleaning and oiling around saddle roller); was successful and follow-up monitoring showed adequate saddle movement
How was SHM used on the West Coast route modernisation project?
- Used to tune and validate bridge assessment models, for introduction of faster and heavier trains
- Several bridges identified as at risk due to resonance, potentially causing ballast liquefaction
- Accelerometers and vertical displacement sensors used
- Information from monitoring fed into FEM to accurately model the dynamic performance of the structures
- Most bridges did not need intervention
What are the two types of data in SHM?
Real-time data, used where:
- item/factor being monitored is critical
- convenient to visualise data without waiting for data gathering
Historical data, used where:
- changes over time are to be seen in context
- monitoring more for long-term planning than safety critical matters
What sampling rate should data be recorded at?
At least twice the maximum frequency component of the signal
What is the a ‘digital twin’, and what is it used for?
A mathematical model that behaves in the same way as the infrastructure:
- built using (large) data obtained from sensors
- model based on predictive analysis, machine learning, AI
Used for detailed behaviour + performance analysis and/or prediction
For this case study, what are the possible causes of defects and damages in the bridge?
- Concrete cracks
- Large strain of the section, or residual deformation
- Caused stress concentration and slippage of the anchor device for cables
- Loss of tendons
- Damage at the joints
For this case study, what monitoring needs and sensors would you install?
This is to confirm validation of the bridge design and inform asset management decisions
- Install comprehensive SHM systems
- Output from the sensors will be the input to a ‘decision support system’, to confirm validation of the bridge design and for the future inspection and monitoring regime
- “System should store and process data for real-time monitoring, have alarms that can be triggered, and automatically generate reports”
For the bridge case-study, where could potential failures occur?
