Acoustic Emission monitoring of bridge structures
Cardiff University have developed techniques in conjunction with Physical Acoustics Limited, to enable a wide range of bridges and bridge components to be monitored for damage.
The bridge work completed was supported throughout by extensive laboratory investigations; from small concrete steel specimens to half scale models of bridge sections. All work completed has contributed to a data base of signals for source identification and information on test parameters for field instrumentation.
A 12m I-beam was used to assess signal attenuation in steel. A fatigue crack was grown in the end of the beam and monitored by sensors up to 12m away. The experiment was repeated by repairing the crack and a fatigue crack re-grown .
Scale Model Box Girders
Three scale models of box girders were fabricated at Cardiff. The models were loaded to simulate normal traffic loading conditions. AE results showed it was possible to accurately locate internal fatigue cracks from sensors mounted to the outer web.
Steel reinforcement bars encased in concrete were loaded in tension to simulate expected bridge load conditions. The test showed that it was possible to distinguish between concrete and steel cracking using sensors mounted to the steel reinforcement bar.
Shear Stud Testing
As part of a Teaching Company Scheme with Physical Acoustics Limited a method for detecting shear stud failure in composite box girder bridges was developed. The technique allowed damaged shear studs to be identified without the excavation of structural concrete.
Completed Bridge Investigations
A preliminary research investigation of acoustic emission signals in steel bridge structures was completed in January 1996 on Trecelyn Viaduct, Newbridge. Information on attenuation, wave propagation and noise on a road bridge was collected and allowed the requirements for monitoring steel bridge structures to be defined.
A second investigation was completed in August 1997 on Saltings Viaduct, Neath. Sensors fixed to the external beam were used to monitor four 30m spans of the bridge structure. The results identified regions of activity coinciding with internal diaphragm positions. Sensors mounted around the diaphragm were then used to locally monitor the diaphragm. A number of regions of possible fatigue cracking were identified.
A commercial investigation of the Bescot Viaduct (M6 Junction 9) followed in February 1999 in association with Physical Acoustics Limited. 34 sensors were used to monitor a 38m span of the bridge structure. After one day of monitoring, two of the most active sources were chosen for local monitoring, and a crack of approximately 250mm was identified and located in a sealing weld.
River Usk Crossing
September 2002 was the first investigation by Cardiff into a steel reinforced concrete bridge; previous work had been confined to steel box girders. A hinge joint on the River Usk Bridge was monitored for a period of 15hrs under normal traffic loading and no damage was detected by Acoustic Emission, this was subsequently confirmed using X-rays