Seismic FDD modal identification and monitoring of building properties from real strong-motion structural response signals

Abstract

Summary In the present study, output‐only modal dynamic identification and monitoring of building properties is attempted successfully by processing real earthquake‐induced structural response signals. This is achieved through an enhanced version of a recently‐developed refined Frequency Domain Decomposition (rFDD) approach, which in the earlier implementation was adopted to analyse synthetic seismic response signals only. Despite that short duration, nonstationary seismic response data and heavy structural damping shall not fulfil traditional Operational Modal Analysis assumptions, the present rFDD response‐only algorithm allows for the effective estimation of strong‐motion natural frequencies, mode shapes, and modal damping ratios, with real seismic response signals. The present rFDD enhancement derives from a preprocessing time‐frequency analysis and from an integrated approach for Power Spectral Density matrix computation, which constitute crucial innovative issues for the treatment of real earthquake response data. A monitoring case study is analysed by taking the real strong‐motion response records from a seven‐storey reinforced concrete building in Van Nuys, California, from 1987 to the latest 2014 events (Center of Engineering Strong Motion Data database), as recorded before, during and after the 1994 Northridge earthquake, which severely damaged the building (then retrofitted). This paper proves the effectiveness of the proposed enhanced rFDD algorithm as a robust method for monitoring current structural modal properties under real earthquake excitations. This shall allow for identifying possible variations of structural features along experienced seismic histories, providing then a fundamental tool towards Earthquake Engineering and Structural Health Monitoring purposes.

Earthquake‐induced structural response output‐only identification by two different Operational Modal Analysis techniques

“…16 This is calculated through a routine of the rFDD algorithm (Section 2.1), by adopting Welch's modified periodogram. 17 Such proposed integration of SSI and FDD information demonstrates here to provide a reliable tool to support the individuation of the stable SSI poles within the stabilization diagram, especially when dealing with earthquake-induced structural response signals and at concurrent heavy damping. • The most severe issue in the present SSI identification keeps lying in the fact that seismic response signals are characterized by rather short durations (specifically with respect to operational vibration recordings).…”

“…In Pioldi et al, 12,13 the theoretical validity and efficacy of the present rFDD technique has been discussed, through the use of synthetic seismic response signals within the linear response range. Trials with real earthquake responses and damage scenarios in the nonlinear response range have been effectively performed in Pioldi et al 17 In Pioldi and Rizzi, 14 further rFDD computational strategies have been introduced, by adopting the complete FEMA P695 earthquake database. In Pioldi et al, 18 the rFDD technique has been also applied to frames under Soil-Structure Interaction (SSI) effects, towards flexible-and fixed-base modal parameter identification.…”

“…16 This is calculated through a routine of the rFDD algorithm (Section 2.1), by adopting Welch's modified periodogram. 17 Such proposed integration of SSI and FDD information demonstrates here to provide a reliable tool to support the individuation of the stable SSI poles within the stabilization diagram, especially when dealing with earthquake-induced structural response signals and at concurrent heavy damping.…”

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

“…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].…”

Denoising Corrupted Structural Vibration Response: Critical Comparison and Assessment of Related Methods

“…This may open up to new perspectives in the post-processing of such signals; in fact, although these techniques have been already tested, for instance, on gravity and magnetic signals, biological signals such as electrocardiograms (ECG) or electroencephalograms (EEG), or even acoustic signals and pressure signals, their application on structural vibrational signals, typical of the civil engineering field, has not been deeply inspected yet. Furthermore, structural response data are crucial for SHM purposes, as their observation over time, also supported by the wide development of modal identification techniques for the acquisition of the structural modal features [14][15][16], may reveal variations in the physical properties of the monitored structure. This might be related to the possible appearance of damage and, consequently, it could lead to a decay of the structural performance characteristics.…”