Feb 15, 2008Last August, 13 people died and about 100 were injured when the I-35W bridge over the Mississippi River in Minneapolis collapsed. The bridge had undergone regular, mandated inspections, and it had been noted that the bridge's bearings and footings were weakening and would need repair. But the inspections relied only on visual checks, so the extent of any damage or weakness was merely an estimate. To better determine a structure's integrity, two Japanese companies have developed a system that uses RFID and sensors to measure strain and deformation from within the concrete.
The Strain Sensing System, developed by Oki Electric Industry Co. and Taiheiyo Cement Corp., includes sensor-integrated steel—basically, standard commercial-grade steel with sensors attached—that can be embedded within concrete. The sensors detect strain levels, deformation and temperature, and communicate their findings to 13.56 MHz passive RFID tags, which are also affixed to the steel and embedded within the concrete, about an inch or two from the concrete structure's front.
Using a handheld RFID reader/writer that leverages an OKI Electric-developed, proprietary air-interface protocol to read the tags, an inspector will be able to collect the structure's precise metrics, as determined by the sensors, and encode onto the tag the date and time the reading occurred, creating an electronic trail of inspections. Software, which is still being developed, will let inspectors, builders and others analyze the current and historical data so they can more accurately determine a structure's integrity.
The two companies demonstrated the prototype system in Tokyo at the Maintenance Techno Show 2007 in November. The system is undergoing on-site testing at Taiheiyo Cement, and a commercial version should be ready in the second quarter of 2008, according to Koichi Sakanashi, manager of the Sensor Network Venture Unit at Oki Electric. The system will initially be marketed to general contractors in Japan by Taiheiyo Consultant Co., which provides consulting and engineering services.
The Strain Sensing System is designed for new construction, so it won't help inspections of the thousands of aging bridges around the world. But with the system, "one can easily measure the burden on the structure or the status of deformation directly," says Sakanashi, making inspections of future bridges and structures more of a science and less of an art.