Combining Model Based and Data Based Techniquesnin a Robust Bridge Health Monitoring Algorithm.

摘要

Structural Health Monitoring (SHM) aims to analyze civil, mechanical and aerospace systems in order to assessnincipient damage occurrence. In this project, we are concerned with the development of an algorithm within thenSHM paradigm for application to civil engineering structures. Vibration-based techniques are the ones considerednto be the most appropriate to perform SHM of civil engineering structures. They are based on the premise thatndamage will alter the properties of the structure, which will be manifested in its dynamic response. Thus, bynmeasuring and analyzing the vibration response time histories it will be possible to detect such changes.nA mixed" approach to vibration based SHM is explored in this project, combining the comparative advantagesnprovided by model based" and solely data based" techniques. A damage sensitive feature (DSF) is defect nusing experimental modal parameters which may be obtained from operational/ambient vibration response of thenstructure. This DSF is proportional to the relative change in any diagonal element of the stiffess matrix of a modelnof the structure, with structural damage being represented as localized stiness reduction. Although the DSF isnderived in a model-based setting, necessary parametric modeling assumptions are kept to a minimum. The DSFsnextracted from measured vibration response data are used to perform damage assessment in a statistical patternnrecognition (data-based) framework, using empirical complementary cumulative distribution functions (ECCDFs)nof the DSFs. The inherent statistical nature of the framework allows for uncertainties induced by measurementnnoise, environmental/ambient eects etc. Methods are discussed to perform a three-fold probabilistic structuralnhealth assessment: (a) Is there a change in the current state of the structure compared to the baseline state?",n(b) Does the change indicate a localized stiness reduction or increase?", with the latter representing a situationnof verification of retro#12;tting operations, and (c) What is the severity of the change in a probabilistic sense?".nParticular effort is made to account for non-damage" related structural variations, induced, for example, byndiurnal temperature changes, using lower and upper bound ECCDFs to defect the baseline structural state. Suchnan approach is intended to decouple normal structural variations from damage induced changes. The damagenassessment procedure is discussed using numerical simulations of ambient vibration testing of a bridge deck system,nconsidering both complete and partial instrumentation scenarios.