BACKGROUND: Civil and environmental engineers from the University of Michigan embedded wireless sensors in a bridge this summer. The sensors can self-diagnose cracks after an earthquake without the need for human intervention. They took measurements for three days, recording vibrations made by different sized trucks driving over the bridge, and found that a wireless network of 14 sensors performed as well as traditional cable-based monitoring systems.
HOW IT WORKS: Miniature computers are integrated into the sensors, so that they can both collect data and monitor the structure for signs of damage. The sensors send electrical signals into the structure. If there is a crack or other damage, it will disrupt the electrical current, and the system will detect and analyze the disruption. The researchers estimate that by 2020, inspectors may no longer need to manually check bridges for damage -- an expensive and labor-intensive process.
BENEFITS: Wireless sensors are potentially much less expensive, more functional and take less time to install and keep up. Each sensor processes data itself, and only the most important data points are sent to a central computer. The sensors can also detect damage that may not be clearly visible to the naked eye. Smart wireless sensors could be fitted into new buildings to give firefighters, for example, early warning of potential structural collapse following explosions.
WHAT'S NEXT: The Michigan Department of Transportation will use the same set of wireless sensors this summer to measure potential crack patterns in a slab of a new concrete material that will be used to retrofit a section of the Grove Street bridge deck in Ypsilanti.
ABOUT STRUCTURAL DESIGN: All modern high-rise buildings and most bridges feature something called redundant design: when one section fails, the entire structure should still be able to stand. It's a bit like a net: lose one string and the net will be weakened, but as a whole, the net still functions. Most high-rise buildings and bridges also are designed to sway in the breeze, because if the structure is too rigid it can snap under too large an impact. The World Trade Center was designed to withstand strong winds striking it from the side, and was even able to absorb the initial impact of an airplane colliding with it on 9/11, although the Twin Towers ultimately collapsed.
The American Society of Civil Engineers contributed to the information contained in the TV portion of this report.