Lifetime assessment and structural health monitoring
There is a wide industrial need for predictive systems that can monitor structures and inform the asset holder on its state of health. These structures could include bridges, buildings, power plant, aircraft, chemical plant etc. Even just considering bridges, a simple clear indication of the structure’s health will provide substantial economic benefits since there are over 10,000 bridges worth more than £1M each in the UK alone. Recent events in the USA and the publicised current state of major suspension bridges in the UK highlights the potential impact of scientific research in this area.
To achieve this aim NPL has created a demonstrator - a 15 tonne, 5 metre high, 20 metre long concrete bridge and the largest specimen ever created at NPL (pictured right). Built in the mid-1960s, and used for more than 40 years, it has recently been moved to create a test bed for many different techniques for monitoring structures. It is important to realise that the real value of this structure is as a specimen; the structure is no longer 'live' and therefore can be artificially aged.
The bridge, which is truly representative of many bridges currently used in the UK's transport infrastructure in terms of construction, age and exposure to corrosion, is currently being subjected to accelerated ageing and loading until it fails. At the same time it is being surveyed and continuously monitored using established and new innovative methods developed by NPL and partners, including Imperial College, City University and many UK SMEs.
By using the structure in this way allows several aims to be achieved. The structure can be used as a demonstrator to show the benefits of SHM to the wider civil engineering community, the structure can also be used as reference specimen to allow sensor suppliers a test bed to assess the performance of their techniques and it can be used to provide information suitable for lifetime predication as the structure undergoes accelerated ageing.
Sensing types planned for NPL demonstrator monitoring
| Sensor Identification | Continuous Monitoring or Surveying Technique | Measurand | Comments |
| NPL DIC | Both | Full field strain, displacement | Will use various camera positions to get full coverage of bridge structure |
| Laser scan | Survey | Shape | University of Liverpool 3D laser scan |
| Scisite | Survey | Rebar corrosion | Survey bridge before accelerated ageing starts |
| FBG | Continuous | Strain | EPSRC project with City University |
| Sensornet | Continuous | Strain | Distributed fibre optic strain sensor |
| Imetrun | Continuous | Strain, displacement | Optical strain gauge technique |
| Acoustic Emission | Continuous | Cracking | Physical Acoustics, Cardiff University to provide data to investigate crack initiation and extension |
| Strainstall | Continuous | Cracking | Innovative sensor |
| SensorBox | Continuous | Crack opening, tilt | Wireless sensor |
| Senscieve | Continuous | Tilt | Wireless sensor |
| Soil Instruments | Continuous | Strain, tilt | Foil and vibrating wire strain sensors, tilt sensors |
Contact
Customer Service tel: +44 20 8943 8681
E-mail: materials_enquiries@npl.co.uk