ABSTRACT
Deterioration of bridges nationwide has prompted the search for new methods to rehabilitate, repair, manage, and construct bridges. As a result, smart structure concepts utilizing structural health monitoring strategies have emerged to help improve bridge construction and management of bridges. By using conventional sensors and robust data processing algorithms, bridge owners are equipped with more timely information on structural performance parameters and maintenance needs. In the case of timber bridges, traditional evaluation and maintenance efforts are typically determined by visual inspection. This report discusses an SHM system currently being developed to continuously monitor the performance parameters of a demonstration timber bridge.
The report details the development of strain and moisture monitoring sensors for inclusion into glued-laminated (glulam) timber components and the monitoring system. A point moisture measurement sensor (PMM) was selected for inclusion in the system because of its reasonable accuracy, excellent survivability under repeated loading, and the ability to be wired into a complete data logging system. Laboratory testing led to the development of strain sensor attached via a metal shim, i.e. the Shim Method, and was found to be simple to fabricate and install and quite robust in field applications.
A data processing technique and specialized algorithm were also developed to identify changes in structural stiffness in timber bridges. The system uses statistical control chart techniques to observe changes in distribution factors and neutral axis locations. The effectiveness of the system was demonstrated by collecting, reducing, and analyzing ambient strain data from the demonstration timber bridge. The developed algorithm allowed for the detection of an applied stiffness change with a 72% violation rate and a 0% violation rate before the stiffness change was applied. The system uses strain measurements to report on the bridge condition and is capable of detecting and zeroing truck events, determining approximate transverse truck position, calculating distribution factors and neutral axis locations, establishing control limits on the stiffness factors, as well as other functions.
Lastly, a bridge weigh-in-motion detection system, utilizing the same strain sensors and monitoring system is under development and testing for incorporation into the timber bridge structural health monitoring system.
The continuous monitoring approach detailed in this report would provide bridge owners with real-time structural integrity information regarding their bridges which would facilitate making maintenance decisions earlier and more effectively. Furthermore, introducing structural health monitoring technologies into the timber bridge industry should result in improved safety, longer service life, and improved load ratings.
