Following the collapse of the steel-arch, deck-truss bridge carrying Interstate 35 over the Mississippi River in 2007 where 13 people were killed and 145 were injured, the University of Michigan will lead a $19 million smart bridge project that will help prevent tragedies of this kind in the future.
The five year project will look at an infrastructure monitoring system that uses surface and penetrating sensors to detect cracks, corrosion and any other signs of weakness that in most cases are only detected by the human eye.
At present it is nearly impossible to measure the effects of heavy trucks on bridges but with this system the scientists believe it will be possible with enhanced antennas and the Internet to wirelessly relay information to a site inspector based miles away.
The cost of bridge maintenance is certainly a problem. According to The American Society of Civil Engineers, "As of 2005, 156,335 of the USA's 595,363 bridges, or 26.3%, were structurally deficient or functionally obsolete. To simply maintain the current condition of these bridges will require an annual $7.3 billion - To eliminate all bridge deficiencies will require $9.4 billion annually for a period of 20 years. Total bridge expenditure by all levels of government for capital outlays (including system preservation and system expansion) was at $8.8 billion in 2003." More money is clearly required to keep all bridges from being structurally deficient and to prevent further problems in the future.
This project will aid the improvement and safety of the nations aging bridges by developing new technologies that will save time and money.
Electrically conducting bendable concrete
Four types of sensors will be used to help gather data. A high performance, fiber-reinforced, bendable concrete that conducts electricity has already been developed. Changes in conductivity would be measured which would send signals to indicate weaknesses in the bridge. On test bridges the deck would be replaced with this concrete.
A sensing skin
A sensing skin based on carbon nanotubes is being developed by the researchers that could be glued or painted on to hot spots on the bridge to detect cracks and corrosion not visible to the human eye. The skin's perimeter is lined with electrodes that run a current over the skin to read what's happening underneath based on changes in the electrical resistance.
Energy harvesting nodes
Low-power, low-cost wireless nodes could look for classical damage responses like strain and changes in vibration. These nodes would harvest energy from vibrations on the bridge or even radio waves in the air and are currently being developed by the team.
Sensor to measure strain
The fourth type of sensor would be housed in the vehicles that travel on the bridge. UMTRI researchers will outfit a test vehicle to measure the bridge's reaction to the strain the vehicle imposes. This information is not available today. But how vehicles, especially trucks, affect bridges is a critical piece of information that could help predict the structure's lifetime. Leading this effort is Research Professor Tim Gordon, head of UMTRI's Engineering Research Division.
The University plan to find partners who can help them commercialize the technology.
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