Acoustic Monitoring
Corrosion of steel tendons in post-tensioned bridges can cause them to fracture, thereby compromising the strength and integrity of the structure. There are many post-tensioned bridges in the UK and elsewhere, so how can infrastructure owners be confident that the structure is not deteriorating? |
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Acoustic Monitoring using SoundPrint®
One method is to subject the structure to a special inspection which includes intrusive drilling into a sample of the post-tensioning ducts and visual examination of the tendons. Such inspections give an indication of risk which then has to be managed. Where there is deemed to be a risk of corrosion and fracture of tendons, interim measures such as lane closures or weight restrictions may be applied. However, these measures have the potential to increase congestion and CO2 emissions and extend journey times.
An alternative does exist: the SoundPrint® monitoring system can be applied to a structure where further deterioration can be tolerated. SoundPrint® can detect and locate wire fractures in steel tendons in grouted post-tensioned ducts, and reject non-wire break events. This was verified in a laboratory trial commissioned by the Highways Agency (HA) and conducted by TRL in 1998.
A further HA funded trial at the Huntingdon Railway Viaduct - a post-tensioned bridge in Cambridgeshire - proved equally successful. Initially, thirty-two acoustic sensors were installed on the northern cantilever span of the bridge and trials of the system, including blind trials using facsimile breaks and external wire breaks, proved the system was working as intended. Long term monitoring of the structure continues to the present day.
How does it work?
SoundPrint® uses surface-mounted sensors to detect the acoustic energy released by the fracture of a stressed steel wire and to locate the position of the break. The system is non-destructive, provides continuous monitoring of the structure and is an extremely cost effective way of monitoring a structure, saving money in unnecessary repairs and premature decommissioning.
Demand for the system is increasing in the UK: recent installations include Bowdon View Bridge - M56 Junction 7: Thorley Lane Bridge - M56 Junction 5, and a major extension to the Huntingdon Railway Viaduct.
SoundPrint® is a proven asset management tool. As well as bridges, the system has also proved to be an effective way of monitoring the fracture of wires in other structures, including buildings and car parks.
Case Study - Bowdon View Bridge
In 2007, the UK's Highway Agency approached TRL to ask them to investigate the integrity of the Bowdon View Bridge, which had been constructed in 1971. TRL subsequently assessed the structure using acoustic monitoring. To find out more details, please click here.
