Abstract
Abstract Structural identification using dynamical parameters (such as the natural vibration frequencies and mode shapes) is an important issue, especially in bridges or high-rise buildings. However, incorrect decisions could happen on the Structural Health Monitoring (SHM) strategy and the Structural System Identification (SSI) analysis that makes the sometimes expensive and time-consuming process useless due to the large uncertainty of the resulting estimations. This paper discusses the role of the SHM strategy and the SSI analysis based on the constrained observability method (COM) and decision trees (DT) in reducing the estimation error. Here, the COM uses subsets of natural frequencies and/or modal-shapes to deal with the nonlinearity of the SSI derived from the operational aspects of the methods, and combines the unknown items including frequencies and mode shapes into an optimization process. Next, a decision-support tool based on decision trees is applied to help engineers to establish the best SHM + SSI strategy yielding the most accurate estimations. The principle and steps of this new method, the combination of constrained observability m,ethod and decision trees, are presented for the first time. After that, a numerical model of a bridge case is used to show how to choose the optimal strategy, when factors such as the structure layout, span length, measurement set, and parameters of the COM are included as decision variables. The importance ranking of these four factors is the layout, measurement set, parameters of the COM, and length through the sensitivity analysis of the COM estimated. Last, a real bridge is used to validate this methodology under the undamaged and damaged scenarios by comparing an Error Index, which shows the optimal SHM + SSI strategy works well no matter the bridge is damaged or not. The presented analysis leads to significant insights that can help the decision-making of the optimal SHM + SSI strategy, avoiding erroneous decisions if this tool is not used beforehand.
Highlights
Structural system identification (SSI) is the process of modeling/ updating an unknown or not perfectly known system [1] and identifying its unknown structural parameters based on the analysis of the structure’s performance when excited statically or dynamically [2]
This paper discusses the role of the Structural Health Monitoring (SHM) strategy and the System Identification (SSI) analysis based on the constrained observability method (COM) and decision trees (DT) in reducing the estimation error
The devices should be located aiming at determining the unknown parameters; (3) measure records given by the SHM are simulated by considering, for each combination of measurement devices, the theoretical values of deforma tion and rotation distorted by a random error consistent with the cor responding device’s lack of accuracy
Summary
Structural system identification (SSI) is the process of modeling/ updating an unknown or not perfectly known system [1] and identifying its unknown structural parameters based on the analysis of the structure’s performance when excited statically or dynamically [2]. The dynamic COM combines the unknown parameters including the theoretical frequencies and mode shapes into an optimization process that minimizes the objective function obtained as the squared sum of the frequencies- and mode shape-related errors. Whereas the SHM focuses on monitoring the actual structural response, SSI aims at determining the actual mechanical properties of the structure based on the observed response Both the monitoring strategy and SSI analysis play an essential role in the uncertainty level of the estimated features. References [27,28,29] show how the sensors’ accuracy, the optimal placement of sensors, and how they are combined highly influence the quality of the estimation These analyses do not consider both the monitoring setting and the characteristics of the method used for SSI as design variables at the same time.
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