Analysis of measurement and simulation errors in structural system identification by observability techniques

Coderque

2017

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SummaryDue to the inevitable noise existing in the measured responses, structural system identification is often a challenging task in terms of the accuracy of the estimations. Structural system identification by the observability method, which is characterized by the analysis of null spaces, is a powerful tool to determine the observability of structural parameters. However, it did not cope well with measurement errors so far. In this paper, for the first time, functional relations among displacements, denoted by the term compatibility conditions, in beam-like structures are derived by the observability method. Then, compatibility conditions are imposed in an optimization procedure to minimize the discrepancy between the measured response and the compatible one. The compatible response obtained by the optimization is used to obtain the final estimations of the parameters. In a simply supported bridge example, the proposed method is thoroughly evaluated regarding the number of measurements, error levels, and load cases. In an example of a continuous bridge, different load cases are used to estimate the bending stiffnesses of different zones. The accuracy and the efficacy of the proposed method are verified by the numerical results.

Section: Example 1 Without Compatibility Conditionsmentioning

confidence: 99%

“…The worse accuracy observed in b EI 3;r compared with those results of b EI 1;r and b EI 2;r are in accordance with a previous study. [35] In fact, for a given load test, the lowest the curvature in a given area of the structure, the worst the accuracy of the estimated parameters in that zone.…”

Section: Example 1 With Compatibility Conditions: Effect Of the Nummentioning

confidence: 99%

Static structural system identification for beam-like structures using compatibility conditions

Coderque

2017

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“…However, wide applications of inclinometers can be found in civil engineering practice, such as stadiums Design Plaza Building , high‐rise buildings, and bridges . In the study of the effect of measurement types on the estimation accuracy in a four‐node simply supported beam, it was found that the rotations were much less sensitive to errors than the vertical deflections . However, systematic investigation on the effect of including rotation measurements on the estimation accuracy in static SSI is lacking.…”

Section: Introductionmentioning

confidence: 99%

“…These essential sets can be found via SSI by constrained OM . In a previous study, the estimation accuracy using essential sets are not satisfactory when measurement error exists . Hence, redundant sets (essential sets plus redundant measurements) are used to reduce estimation errors.…”

Section: Introductionmentioning

confidence: 99%

Structural system identification by measurement error‐minimizing observability method

Galant

et al. 2019

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Summary This paper proposes a method for the finite element model updating using static load tests under the framework of observability analysis. Previous works included measurement errors in the coefficient matrix of the observability equations. This impeded the obtainment of accurate estimations. To deal with this issue, the proposed method relocates the errors and incorporates an optimization procedure to minimize the square sum of these errors. This method is able to identify the structural parameters of complex structures where the axial and bending behaviors are coupled, such as inclined beams or frame structures. Its application is illustrated by three structures. First, the method was validated in a beam‐like structure by comparing it with other methods in the literature. Then the effects of different factors were investigated in a multistory frame and a rigid frame bridge with inclined piers. These factors include the curvatures, the inclusion of rotation measurements, and the constraints on the range of unidentifiable parameters. The importance of rotation measurements is demonstrated in static structural system identification.

“…The parameters of physics‐based models represent the structural characteristics, for example, elastic modulus, inertias, and mass, whereas the parameters of the nonparametric models are weight factors of the adopted basis functions, which have no physical meaning and are determined by minimizing the discrepancy between the predicted and the measured response. From a statistical perspective, SSI methods can be categorized as probabilistic methods or deterministic methods . In the probabilistic methods, structural parameters are treated as random variables and their distributions are specified using prior knowledge.…”

Section: Introductionmentioning

confidence: 99%

Constrained observability method in static structural system identification

Nogal

Galant

et al. 2017

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SummaryIdentifiability of parameters in structural system identification (SSI) is of primary importance in any SSI method. It depends on the number and the location of the measurements, which is linked with sensor configuration. In this paper, under the framework of SSI by observability method (OM), the number of necessary measurements to identify all parameters of structural system was clarified first. Then, an example was solved step by step to show the lacking constraints among unknowns in SSI by OM. In a frame example, it was found that no measurement set having as many measurements as the number of unknowns was able to identify all parameters. To further understand this phenomenon, the observability of a simply supported beam was analyzed in an exhaustive way using 252 possible measurement sets. Three quarters of these sets were not able to identify all the parameters. In order to solve this issue, for the very first time, SSI by constrained observability method (COM), which appends the nonlinear constraints to SSI by OM, was proposed. With SSI by COM applied, the observability of the structural parameters with respect to the 252 sets was greatly improved. Finally, the efficacy of SSI by COM was verified by a 13-story frame building.