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Dynamic Characterization of a Truss Bridge by Falling Weight Deflectometer

Several full-scale testing methods can be used to characterize and evaluate the global performance and condition of a bridge. These global methods consist of mainly static load tests and dynamic tests that use controlled or uncontrolled dynamic excitation. Each approach has advantages and disadvantages for experimental and logistical considerations, data analysis requirements, and scope and utility of the characterization results obtained. This paper presents a global dynamic characterization program based on controlled impact dynamic testing that was applied to a truss bridge. The impact testing was performed with a hand-held impact hammer and a falling weight deflectometer (FWD) as dynamic excitation sources. The objective of the project was to evaluate whether the FWD, which could produce a broadband dynamic force, could be an effective tool for the quantitative characterization of bridge performance and condition. Many transportation agencies already use FWD devices for their pavement evaluation programs, and it follows that if the device is suitable for the impact dynamic testing of bridges, then agencies also can use FWDs to evaluate bridges quantitatively. Dynamic testing approaches are discussed, and an impact dynamic testing program executed for the truss bridge is presented. The results obtained with the two dynamic excitation devices are presented and compared with each other and with the results from an analytical model of the bridge. Finally, several observations and conclusions related to the efficacy of FWD devices for the impact dynamic testing of bridges are presented and discussed.