Networked Structural Health Monitoring

Project Overview

Structural Health Monitoring (SHM) is a highly interdisciplinary area of research focused on developing techniques to detect damage in structures such as buildings, bridges, aircraft, ships and spacecraft. Most SHM research to date has focused either on global damage assessment techniques using low-resolution measurements of a structure's response to ambient excitation, or on limited independent damage detection mechanisms.

This proposal advocates a paradigm shift in SHM, using decentralized local excitation and high-resolution measurements of response to these excitations, detected and collaboratively analyzed through a spatially dense wireless network of devices. This shift promises simpler and more accurate techniques to identify and even localize damage within the structure.

Local excitations can be delivered by shoebox-sized electromagnetic exciters or by coin-sized piezo-electric patches. Such excitations will need measurements at fine spatial scales. Given the prohibitive cost of wiring large structures, these high-resolution measurements will need to be made using untethered (wireless, battery-powered) components. This is now becoming possible with the emergence of small form factor wireless computing devices containing on-board MEMS sensors. That these devices are battery-powered and use wireless communication fundamentally impacts our approach: measurements, damage inference, and damage detection are performed within the network formed by these devices.

Fundamentally, then, this proposal seeks to investigate issues in the design of a networked computer system, with distributed actuation and sensing, for SHM. The term networked SHM denotes the class of monitoring systems that will be enabled by this research. In combining local excitation with high-resolution sensing, networked SHM is quite distinct from other sensor network applications being examined today. Networked SHM promises a future where, for example, buildings are constructed using concrete mixed with several tens of thousands of embedded sensor devices as well as low-power local exciters. The network of sensors will be able to continuously monitor the structure, trigger alarms that identify the onset of damage, precisely pinpoint the location of damage and also provide a long-term history of ambient stresses imposed on the building.

Our focus is on the development of a scalable and robust software infrastructure for networked SHM. Such an infrastructure will enable rapid development of networked SHM systems for a variety of structures. This proposal plans to examine qualitatively different structures (a long-span bridge, and aerospace fuselage skins) using two methodologies: dynamic numerical simulations on structural finite element models interconnected with a network simulator, and experimental studies on scale models. This examination will focus on the principles underlying networked SHM: What health assessment techniques work? For what kinds of structures? How do they impact network design and evaluation? How can robotic elements, and careful positioning of exciters, enable accurate and efficient damage assessment? What kinds of data storage and access issues arise in damage assessment of structures with dense sensor arrays?

Health monitoring and preventive maintenance on large structures will significantly reduce operational costs and increase the lifetime of structures. By enabling early detection of damage, networked SHM systems can promote public safety as well. The associated educational and outreach plan is designed to amplify this impact, and increase the country's economic competitiveness in structural health monitoring, by introducing networked SHM at various levels of the educational system: into the graduate curriculum to broaden engineering students' exposure to multidisciplinary ideas, to the undergraduate research experience to foster interest in graduate studies, to the research experience for school teachers to enable them to instill interest in science among children, and to the academic research community by making datasets, benchmarks and tools readily available.

Faculty

Students

Publications

N. Xu, S. Rangwala, K. Chintalapudi, D. Ganesan, A. Broad, R. Govindan, D. Estrin, A Wireless Sensor Network for Structural Monitoring, In: Proceedings of the ACM Conference on Embedded Networked Sensor Systems (Sensys), pp. 13--24, ACM Press, November 2004. [PDF]

Software

Wisden is a wireless structural data acquisition system. Here is code that integrates ToSSIM (the TinyOS simulator) with a structural simulator.

Acknowledgements

This material is based upon work supported by the National Science Foundation under Grant No. 0325875. Any opinions, findings and conclusions or recomendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).