It seems like a sophisticated signal processing might be able to detect changes in resonance frequency of stuctural membors as a crack propogates. At least of the crack is not right at the end of the piece (where most cracks are likely to initiate!). I like the idea of something like this. I agree, strain is probably impossible to implement effectively.
The variety of sensor measurements that could be made is quite extensive. Strain might be one of the more difficult measurements to make (and identifying the locations to make the measurement might be a problem). If we can find some smart materials where things like strain could be easily measured because the 'strain gage' is 'integrated' into the material that would be fantastic. Anyone know of any work going on it that area that might apply?
I think these sensor networks would be continuously monitoring many factors affecting the structural integrity of the bridge, including strain, tilt, deformation etc., as well as vibration, making sudden failure scenarios under any normal circumstances seem quite remote.
We had a bridge collapse here in WA State a couple of months ago. Part of the issue was repeated strikes by 'oversized' trucks to the upper girders. A sensor array that could just measure some 'out of specification' vibrations would probably have helped identify an issue which could have been corrected prior to failure. Now, if the failure happens RIGHT AFTER a quick series of strikes, maybe it doesn't help much, but if the strikes happen over a period of time thats when sensors would help.
I should think this (i.e., sensors embedded in all manner of infrastructure along with public access to the data) will become commonplace at some point. We are increasingly using them in vehicles, buildings and even our bodies to vastly improve monitoring of real-time "operating conditions." The benefits for doing so with infrastructure are equally clear - just on a larger scale.
@docdivakar, Interesting about MEMS sensors and earthquakes. USGS (United States Geological Survey) has been using MEMS for a while now. Here's a paper from 2005: "TREMOR: A wireless MEMS accelerograph for dense arrays" and additional info here. I don't have time to search for more right now, but if you find an interesting link, feel free to post it in this discussion forum.
@Susan: Regarding "What would these MEMS sensors do in an earthquake?", they can provide VERY valuable data on transmissibility of the ground motions to the structure which is dependent on the structure's toplogy, mass and support conditions. That is the most valuable data input needed for prognostics.
@Peter: I agree and I think that is what Susan, I and some of us are mentioning about. This is the direction to which the world is moving - Prognostics: proactive health checking and planning necessary maintenance schedule well in advance to safeguard the structures.. As you said, surely there will be companies providing this kind of services. This is certainly not aiming towards frightening the travelers with warning that something bad could occur.