Some advances in extensive bridge monitoring using low cost dynamic characterization

Dynamic measurements will become a standard for bridge monitoring in the near future. This fact will produce an important cost reduction for maintenance. US Administration has a long term intensive research program in order to diminish the estimated current mainte- nance cost of US$7 billion per year over 20 years. An optimal intervention maintenance pro- gram demands a historical dynamical record, as well as an updated mathematical model of the structure to be monitored. In case that a model of the structure is not actually available it is possible to produce it, however this possibility does not exist for missing measurement records from the past. Current acquisition systems to monitor structures can be made more efficient by introducing the following improvements, under development in the Spanish research Project "Low cost bridge health monitoring by ambient vibration tests using wireless sensors": (a) a complete wireless system to acquire sensor data, (b) a wireless system that permits the localiza- tion and the hardware identification of the whole sensor system. The applied localization sys- tem has been object of a recent patent, and (c) automatization of the modal identification pro- cess, aimed to diminish human intervention. This system is assembled with cheap components and allows the simultaneous use of a large number of sensors at a low placement cost. The engineer's intervention is limited to the selec- tion of sensor positions, probably based on a preliminary FE analysis. In case of multiple set- ups, also the position of a number of fixed reference sensors has to be decided. The wireless lo- calization system will obtain the exact coordinates of all these sensors positions. When the selection of optimal positions is difficult, for example because of the lack of a proper FE mod- el, this can be compensated by using a higher number of measuring (also reference) points. The described low cost acquisition system allows the responsible bridge administration to ob- tain historical dynamic identification records at reasonable costs that will be used in future maintenance programs. Therefore, due to the importance of the baseline monitoring record of a new bridge, a monitoring test just after its construction should be highly recommended, if not compu lsory.