Subspace-based damage detection under changes in the ambient excitation statistics

Abstract

In the last ten years, monitoring the integrity of the civil infrastructure has been an active research topic, including in connected areas as automatic control. It is common practice to perform damage detection by detecting changes in the modal parameters between a reference state and the current (possibly damaged) state from measured vibration data. Subspace methods enjoy some popularity in structural engineering, where large model orders have to be considered. In the context of detecting changes in the structural properties and the modal parameters linked to them, a subspacebased fault detection residual has been recently proposed and applied successfully, where the estimation of the modal parameters in the possibly damaged state is avoided. However, most works assume that the unmeasured ambient excitation properties during measurements of the structure in the reference and possibly damaged condition stay constant, which is hardly satisfied by any application. This paper addresses the problem of robustness of such fault detection methods. It is explained why current algorithms from literature fail when the excitation covariance changes and how they can be modified. Then, an efficient and fast subspace-based damage detection test is derived that is robust to changes in the excitation covariance but also to numerical instabilities that can arise easily in the computations. Three numerical applications show the efficiency of the new approach to better detect and separate different levels of damage even using a relatively low sample length.

Subspace-Based Damage Detection on Steel Frame Structure Under Changing Excitation

“…Hence, the residual ζ and the corresponding test value χ 2 are influenced by changes in the ambient excitation, which may lead to false alarms. Due to these reasons, a robust variant of the presented damage detection test was derived in [6]. It is based on the property that the Hankel matrix H p+1,q and the matrix of its principal left singular vectors U 1 (see SVD in (7)) share the same left null space S -another characteristic property of the reference state can be written as…”

“…is defined [6]. It is tested if this residual is significantly different from zero or not, using the χ 2 test…”

“…In this paper we consider the subspace-based damage detection approach developed in [2,3,5,6]. With this approach, a data-driven model obtained in the reference state is compared to data from the possibly damaged state using a subspacebased residual function and a χ 2 -test built on it for a hypothesis test, without actually estimating the modal parameters in the tested, possibly damaged states.…”

“…Recently, the original algorithms have been extended and modified to be robust under such changes in the excitation in [6]. This approach has been shown to be promising under changing excitation in numerical simulations [7,12,6].…”

“…This paper is organized as follows. In Section 2, the basics of the considered damage detection approach are presented and in Section 3 the extension from [6] that is robust to changing ambient excitation. In Section 4, a numerical application is presented on a simulated truss, as well as a case study on a steel frame structure in the lab that was artificially damaged.…”