Blind modal identification of non-classically damped structures under non-stationary excitations

Abstract

Summary In the present paper, we extend a previously developed blind modal identification method to systems with non‐classical damping, which have complex‐valued mode shapes. Unlike conventional output‐only identification methods, blind modal identification method can provide modal property estimates when the input excitations are unknown and non‐stationary (e.g., for systems equipped with added dampers or soil–structure problems). In earlier work, we have developed a technique that can be used for non‐classically damped systems, but it is only applicable to stationary (i.e., ambient) excitations. Herein, we present an extension to non‐classically damped systems under non‐stationary (e.g., seismic) excitations. The proposed method yields mode shapes, natural frequencies and damping ratios, sequentially. A critical ingredient in this new method is a combination of generalized eigen‐decomposition and rough–fuzzy c‐means clustering techniques, which are employed to identify the complex‐valued mode shapes. The accuracy of the proposed method is verified through a simulated but realistic example. Copyright © 2016 John Wiley & Sons, Ltd.

Optimum Tuning of Passive Tuned Mass Dampers for the Mitigation of Pulse-Like Responses

“…In Table 1, the percentage magnitudes of analytical response reduction, in terms of x 1 (t) ∞ and x 1 (t) 2 norms have been gathered, which, for the SDOF primary structure alone, are represented by Eqs. (13) and (14) respectively (Section 2.2), for values ζ 1 = [0, 0.03, 0.05] and µ = [0.02, 0.05, 0.1]. One may observe that the peak response abatement is rather small, also for significant values (from an engineering application point of view) of mass ratio µ, and it exhibits a high insensitivity on structural damping ratio ζ 1 .…”

“…The assumption of ground motion in terms of absolute base displacement shall provide two main considerable advantages: a) it allows for an easier formulation than that in the case of a relative ground acceleration; b) it is more suitable from the viewpoint of real dynamic response measuring, which turns out to be feasible when focused on the detection of absolute coordinates rather than on the relative motion between the masses of the system. These reasons may even look more important in the case of a MDOF primary structure, which may reflect real engineering contexts and represent a generalisation scenario of the present SDOF analysis, maybe also involving the adoption of Multiple TMDs [5,7,9] or the issue of TMD positioning along the structure [16] and of structural system identification related contexts [13,[29][30][31], possibly in the contextual presence of vibration control devices [47], and/or of specific characteristic structural effects, like Soil-Structure Interaction [15-17, 32, 40].…”

Damage detection in structural systems utilizing artificial neural networks and proper orthogonal decomposition

“…53 Ghahari et al performed an investigation of ICA for nonstationary signals using Rough-fuzzy, c-means clustering . 13 The focus was on extraction of damage features from short-term, nonstationary, external excitations that potentially occur at discrete single intervals, such as during passage of heavy truck or train across a bridge. Although the methodology was sound, ICA required complicated and timeconsuming, algorithmic solutions.…”

“…In many cases such assumptions might be violated, and consequently, modal properties would not be identified in a consistent manner. Research to address issues caused by nonstationary external inputs is in progress …”

“…Research to address issues caused by nonstationary external inputs is in progress. 13,14 In addition to uncertainties stemming from modal identification, modeling errors also affect damage estimates. Moaveni et al performed shake table tests of a full scale, seven story reinforced concrete building to study uncertainties in common damage detection methods.…”