Wireless warning for earthquakes

US research could lead to a network of wireless sensors mounted on bridges that will continually report their safety and performance in everyday use and after catastrophes.

Yunfeng Zhang, an assistant professor of civil and environmental engineering at Lehigh University, Philadelphia, is setting out to prove that sensors deployed strategically on a bridge can provide a high-resolution, multi-dimensional picture of the health of a structure, giving engineers vital information about a bridge's performance and, in the aftermath of a catastrophe, its ability to carry traffic.

To be useful in the event of an earthquake or other emergency, said Zhang, sensor data must be transmitted in real time to remote processing centres for interpretation and then sent on to decision-makers.

Zhang’s research aims to improve the transmission of sensor data and ease of access to the data. Wireless sensor networks avoid many of the problems that hamper wired sensors, such as degradation, interference and damage. But the relatively narrow communication bandwidth available for civil engineering wireless sensors can reduce download rates to one kilobyte per second, not nearly fast enough to crunch the enormous amounts of data generated by a bridge in operation.

To improve data transmission and management, Zhang is developing high-performance sensor data compression algorithms for structural health monitoring applications. His algorithms incorporate structural system information to remove redundancies from sensor data and maximise the compression rates for sensor network data. Zhang also uses data-mining techniques to extract key information more efficiently from data.

As part of his project, Zhang plans to implement a wireless sensor network on a cable-stayed bridge in eastern China to monitor its structural health and operating condition. The bridge, built in 2000, was accidentally damaged during construction, so its actual operating condition is different from its design condition. The bridge was repaired and is operating, but aggressive monitoring is needed to ensure that it can continue to be safely used by traffic.

Using wireless sensor networks that Zhang will help develop, Zhang and the Chinese engineers are planning to conduct a full-scale validation test on the Chinese bridge in 2009.