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Bridge health monitoring...a radical approach using Wi-Health to structural defect detection

14 February 2012
Bridge health monitoring 1

The Wi-Health project aims to develop an autonomous, wireless and self-powered sensor network that will provide long term and continuous structural health monitoring (SHM) of bridges using a minimal number of network nodes and sensors.

The objectives of this EU funded collaborative project are to improve structural defect detection at an early stage before the defects cause serious damage, and this should greatly reduce the costs of repairing damage.

Maintaining the structural integrity of safety critical items of bridges becomes increasingly difficult as they age. A vital part is the periodic inspection for detecting defects such as fatigue cracks and corrosion that are not always visible during a typical manual or visual inspection but may lead to catastrophic failure.
There are several aspects that need to be considered in periodic inspections solely using traditional techniques.

However defects may grow to failure between inspections. Access to conduct the inspection may be poor and it may be difficult to determine the significance of any defect that has been detected. Is failure imminent or can the defect be left until a more propitious time for repair?

So there is strong interest in replacing periodic inspections with continuous structural health monitoring (SHM), using networks of sensors, which are permanently installed on the structure and sensitive to the defect. Where these structures are very large, wireless sensor networks offer significant benefits.

The proposed sensor network will be multi-purpose. The acoustic emissions (AE) that are a consequence of active defect growth will be detected by sensors in network nodes permanently installed at damage-prone areas of the bridge such as welds, plates and expansion joints.

The AE will be used to activate ultrasonic guided wave (UGW) transducers at the same nodes that will flood the source of the AE with ultrasound in such a way that UGW reflections can be used to determine the nature, size and exact location of the defect. This information is needed to assess the defect in terms of the structure’s fitness for purpose.

As data streams are very dense, they will have to be processed and reduced by an order of magnitude in a central processing unit (CPU) at the network node before being transmitted wirelessly. Innovative embedded software will be able to drive the structural health monitoring system for defect identification by incorporating the use of trend analysis and data processing.

The Wi-Health concept will give much greater confidence that catastrophic failures will not occur. It will replace unreliable periodic inspections with a continuous early warning system for structural irregularities that are not visible by external inspection alone.

The Wi-Health Project is a collaborative project, funded by the European Union under the FP7 framework, under grant agreement no 283283.

For further information on the Wi-Health Project please contact Mrs Kamer Tuncbilek, TWI Ltd on +44 (0)1223 899197 or email Email: kamer.tuncbilek@twi.co.uk or www.wi-health.eu.