Issues in health monitoring for intelligent infrastructure

The US Federal Reserve Board has concluded that the failure of civil infrastructure systems to perform at their expected level may reduce the national gross domestic product (GDP) by as much as 1%. Intelligent-infrastructure systems and components hold promise for improving performance with an excellent cost/benefit ratio. A recent National Science Foundation (NSF) workshop demonstrated the state of the art in research and applications on intelligent materials and structures in Japan and the US. Major investments have been made by the leading Japanese construction companies into developments for enabling intelligent-structure applications for mitigating earthquake and wind damage. A number of innovative concepts and ideas have been developed by American researchers; however, a lack of applications has also become apparent.

This paper reports on the research of a multidisciplinary team working at the University of Cincinnati Infrastructure Institute to conceptualize a wide spectrum of issues in infrastructure condition assessment, health monitoring and intelligent systems by conducting exploratory research on actual operating highway bridges. The writers have made much progress towards developing an intelligent-bridge application. Such an application requires advances in sensors, communication and information technology, global non-destructive evaluation technologies of a rigorous and objective nature and fundamental knowledge on state parameters, loading environments, damage and deterioration mechanisms and performance of actual highway bridges. The writers initiated a strong university-government-industry partnership a decade ago and have explored a global condition assessment methodology based on the structural identification concept. After a decade, they have reached an in-depth realization of the complex multisystem identification and integration which must accompany any `intelligent' systems approach to the infrastructure problem.

The writers are currently maintaining three `typical' steel-stringer highway bridge overpasses as generic test-sites for intelligent structures, condition assessment and health monitoring. One of these bridges, which is forty years old, has been decommissioned. This specimen is being tested to understand damage limit-state behavior. Another ten year old specimen has been tested and monitored for five years to understand operating loading environment and behavior at service limit-states. The third bridge is being monitored during its construction to understand the causes and magnitudes of intrinsic forces. After commissioning, this bridge will have a built-in monitor with 300 embedded/attached sensors, a weigh-in-motion scale and sufficient on-site hardware and software to create an intelligent-bridge prototype. By taking advantage of the linkages provided by research at all three test-sites, it has been possible to understand the complete life-cycle spectrum of loading effects and behavior of the medium length steel-stringer bridge type.