United States Department of Transportation
i
Combining Model Based and Data Based Techniques in a Robust Bridge Health Monitoring Algorithm
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2014-09-01
[PDF-17.18 MB]
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TRIS Online Accession Number:01555792
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Edition:Final Report
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Abstract:Structural Health Monitoring (SHM) aims to analyze civil, mechanical and aerospace systems in order to assess incipient damage occurrence. In this project, the authors are concerned with the development of an algorithm within the SHM paradigm for application to civil engineering structures. Vibration-based techniques are the ones considered to be the most appropriate to perform SHM of civil engineering structures. They are based on the premise that damage will alter the properties of the structure, which will be manifested in its dynamic response. Thus, by measuring and analyzing the vibration response time histories it will be possible to detect such changes. A “mixed” approach to vibration based SHM is explored in this project, combining the comparative advantages provided by “model based” and solely “data based” techniques. A damage sensitive feature (DSF) is defined using experimental modal parameters which may be obtained from operational/ambient vibration response of the structure. This DSF is proportional to the relative change in any diagonal element of the stiffness matrix of a model of the structure, with structural damage being represented as localized stiffness reduction. Although the DSF is derived in a model-based setting, necessary parametric modeling assumptions are kept to a minimum. The DSFs extracted from measured vibration response data are used to perform damage assessment in a statistical pattern recognition (data-based) framework, using empirical complementary cumulative distribution functions (ECCDFs) of the DSFs. The inherent statistical nature of the framework allows for uncertainties induced by measurement noise, environmental/ambient effects etc. Methods are discussed to perform a three-fold probabilistic structural health assessment: (a) “Is there a change in the current state of the structure compared to the baseline state?”, (b) “Does the change indicate a localized stiffness reduction or increase?”, with the latter representing a situation of verification of retrofitting operations, and (c) “What is the severity of the change in a probabilistic sense?”. Particular effort is made to account for “non-damage” related structural variations, induced, for example, by diurnal temperature changes, using lower and upper bound ECCDFs to define the baseline structural state. Such an approach is intended to decouple normal structural variations from damage induced changes. The damage assessment procedure is discussed using numerical simulations of ambient vibration testing of a bridge deck system, considering both complete and partial instrumentation scenarios.
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