Bridge safety, no strings attached
An earthquake strikes a large city, wrecking roads and bridges, stranding rush-hour commuters, trapping office workers inside high-rise buildings.
As director of the city's transportation authority, you have minutes to make a momentous decision. What is the safest, fastest route that rescue teams can take to travel to hard-hit areas of the city? Which bridges, even if damaged, can still support traffic loads?
The answers, says Yunfeng Zhang, can be provided by sensors – networks of tiny sensors embedded in computer chips that are attached to a bridge to monitor its structural integrity and performance.
Sensors deployed strategically on a bridge, says Zhang, assistant professor of civil and environmental engineering, can provide a high-resolution, multidimensional picture of a critical part of the structure, giving engineers vital information about the bridge's performance and, in the aftermath of a catastrophe, its reliability.
To be useful in the event of an earthquake or other emergency, says Zhang, sensors must be able to transmit data in real time, virtually without delay, to the processing centers where data is interpreted.
Zhang this year received a five-year NSF CAREER Award to develop wireless sensor networks for bridges and other structures and thus improve the transmission, storage and retrieval of sensor data. The project is titled "Integrated Research and Education in Smart Sensing and Intelligent Structures Technology."
Wireless sensor networks, which are relatively new, avoid many of the problems that plague wired sensors. But they face obstacles. The relatively narrow communication bandwidth available for civil-engineering wireless sensors can reduce download rates to 1 kilobyte per second, not nearly fast enough to crunch the enormous amounts of data generated by a bridge in operation.
To overcome this limitation and improve data transmission and management, Zhang is developing high-performance data-compression algorithms for structural monitoring. His algorithms incorporate structural system information to remove redundancies and maximize the data's usefulness. Zhang also uses data-mining techniques to more efficiently extract key information from data.
Zhang's research draws on computer science, information technology and electrical engineering, as well as structural engineering.
As part of his NSF project, Zhang plans to implement a wireless sensor network on a cable-stayed suspension bridge in eastern China to monitor its structural health and operating condition. The bridge, built in 2000, was accidentally damaged during construction, and its actual operating condition is thus different from its design condition. The bridge was repaired and is operating, says Zhang, but aggressive monitoring is needed to ensure that it can continue to be safely used by traffic.
Using wireless sensor networks that he will help develop, Zhang and Chinese engineers are planning to conduct a full-scale validation test on the Chinese bridge in 2009.
Zhang says the data he collects from testing the Chinese bridge will also be useful for bridge operators in the U.S., where cable-stayed bridges have only recently come into use and have not yet generated a large body of data.
As part of his NSF award, Zhang is incorporating his research into his classes. Last spring, Zhang taught an upper-level undergraduate course in smart structure technology that he first taught as a graduate course in 2004.
In the course, students constructed a Japanese pagoda and attempted to shed light on an ancient mystery – why, in earthquake-plagued Japan, the wooden temples have for centuries withstood seismic forces much better than any other type of structure.
Zhang believes the smart structure technology course is the first civil engineering course in the U.S. to integrate sensors, communications, data-mining, information technology, structural engineering and structural health monitoring. Twelve senior civil engineering majors and five grad students enrolled in the course.
"I want to educate the next generation of engineers about an exciting technology that has broad future applications," says Zhang. "Smart structure technology is only in its developmental stages, but as educators, we need to plan ahead so that when this technology is available in 10 years, our graduates will know how to utilize it."