Bridge safety: System uses acoustic emission to detect compromised suspension cables

As part of a range of measures to safeguard the M48 Severn Suspension Bridge, authorities plan to install a full acoustic emission wire-break detection system for 1,673 meters of each suspension cable. See photo.
By Control Engineering Staff August 28, 2008

Princeton Junction, NJ Physical Acoustics Limited (PAL), 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 in the UK.

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 1,673 m (5,487 ft) 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 36 m along the cable. These passive sensors detect and amplify signals from within the main cable. These data are then processed automatically by one of six local “sensor highway” systems distributed along the bridge on an optical fiber 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 synchronized 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
Control Engineering
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