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Bridge safety

01 September 2008

Physical Acoustics Limited (PAL), an international division of MISTRAS Group Inc, has teamed up with Severn River Crossing (SRC) and the Highways Agency to monitor the main cables of the M48 Severn Suspension Bridge, which links England to South Wales.

The M48 Severn Suspension Bridge, which opened in September 1966, has recently undergone invasive investigation of the main cable that revealed corrosion in the individual steel wires and a small number of broken wires. As part of a range of measures to safeguard the structure, SRC appointed PAL to supply and install a full Acoustic Emission (AE) wire-break detection system over the whole 1,673m of each cable.

The acoustic monitoring system listens continuously for sounds from individual wires within the main cable to keep track of the rate and location of any further wire breaks. It uses 90 acoustic emission sensors attached to cable clamps every 36m along the cable. These passive sensors detect and amplify signals from within the main cable. This data is then processed automatically by one of six local ‘sensor highway’ systems distributed along the bridge on an optical fibre network.

PAL says the use of distributed monitoring systems significantly reduces the amount of cabling required, installation cost, and weight. The six sensor-highway systems are synchronised and report to a base-station on the network, which further processes data and automatically reports time and location of potential wire breaks through a secure Website by email, enabling very efficient, low cost, long term monitoring.

The monitoring system will enhance the ability of the Highways Agency to evaluate the health of this structure and pinpoint regions that might require further invasive cable investigation, currently planned for 2010.

— C.G. Masi, senior editor


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