ABSTRACT

Economic barriers to the replacement of bridges and other civil structures have created an aging infrastructure and placed greater demands on the deployment of effective and rapid health monitoring methods. To gain access for inspections, structure and sealant must be removed, disassembly processes must be completed and personnel must be transported to remote locations. Reliable Structural Health Monitoring (SHM) systems can automatically process data, assess structural condition, and signal the need for specific maintenance actions. They can reduce the costs associated with the increasing maintenance and surveillance needs of aging structures. The use of in-situ sensors, coupled with remote interrogation, can be employed to overcome a myriad of inspection impediments stemming from accessibility limitations, complex geometries, the location of hidden damage, and the isolated location of the structure. Furthermore, prevention of unexpected flaw growth and structural failure could be improved if on-board SHM systems were used to regularly, or even continuously, assess structural integrity. A research program was completed to develop and validate Comparative Vacuum Monitoring (CVM) sensors for crack detection. Sandia National Labs, in conjunction with private industry and the U.S. Department of Transportation, completed a series of CVM validation and certification programs aimed at establishing the overall viability of these sensors for monitoring bridge structures. Factors that affect SHM sensitivity include flaw size, shape, orientation and location relative to the sensors, along with operational environments. Statistical methods using one-sided tolerance intervals were employed to derive Probability of Flaw Detection (POD) levels for typical application scenarios. Complimentary, multi-year field tests were also conducted to study the deployment and long-term operation of CVM sensors on aircraft and bridges. This paper presents the quantitative crack detection capabilities of the CVM sensor, its performance in actual operating environments, and the prospects for structural health monitoring applications on a wide array of civil structures.