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PAL PROVIDES SEVERN RIVER CROSSING WITH AE MONITORING FOR LONG-TERM EVALUATION OF SUSPENSION BRIDGE CABLES
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PAL PROVIDES SEVERN RIVER CROSSING WITH AE MONITORING FOR LONG-TERM EVALUATION OF SUSPENSION BRIDGE CABLES

Princeton Junction, NJ - July 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 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, which include the installation of a main cable dehumidification system, SRC appointed PAL to supply and install a full Acoustic Emission (AE) wire-break detection system over the whole 1673 meters 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. The Physical Acoustics monitoring system will enhance the ability of the Highways Agency to evaluate the health of this structure and to pinpoint regions that might require further invasive cable investigation, currently programmed to take place in 2010. This work is all part of the effort by the Highways Agency and Severn River Crossing to ensure the continued integrity and safety of the M48 Severn Bridge.

The monitoring system 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, which are then processed automatically by one of six local Sensor Highway systems distributed along the bridge on an optic fibre network. The use of distributed monitoring systems significantly reduces the amount of cabling required, and installation cost and weight. The six Sensor Highway systems are synchronized and report to a "base-station" on the network. This further processes the data and automatically reports the time and location of potential wire breaks through a secure website by email, enabling very efficient, low cost, long term monitoring.

AE is a global non-destructive evaluation (NDE) and structural integrity monitoring technique. A key advantage of the method is its ability to detect and locate only active flaws, making it a prime candidate for real-time continuous health monitoring of highway bridges. This method is also able to direct local NDT straight to potential problem areas, while ignoring inactive flaws that are not a threat to integrity. Physical Acoustics Ltd installed the monitoring system with subcontract services from CAN Structures Ltd, EPL Access, DCI Electrics Ltd and Electra-Net (UK) Ltd.

Physical Acoustics Ltd offers a wide range of structural monitoring services to bridge and structural engineers which includes fatigue assessment, concrete microfracture and post tension in concrete wire break detection. Monitoring techniques used include Acoustic Emission, vibration, displacement, rotation, strain and temperature. Non destructive testing techniques practiced by Physical Acoustics include ultrasonics (A-scan, B-Scan, C-scan, TOFD, and shear wave), ACFM, eddy current, and Impact Echo.
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