Response‐only modal identification of structures using strong motion data

Abstract

SUMMARY Dynamic characteristics of structures — viz. natural frequencies, damping ratios, and mode shapes — are central to earthquake‐resistant design. These values identified from field measurements are useful for model validation and health‐monitoring. Most system identification methods require input excitations motions to be measured and the structural response; however, the true input motions are seldom recordable. For example, when soil–structure interaction effects are non‐negligible, neither the free‐field motions nor the recorded responses of the foundations may be assumed as ‘input’. Even in the absence of soil–structure interaction, in many instances, the foundation responses are not recorded (or are recorded with a low signal‐to‐noise ratio). Unfortunately, existing output‐only methods are limited to free vibration data, or weak stationary ambient excitations. However, it is well‐known that the dynamic characteristics of most civil structures are amplitude‐dependent; thus, parameters identified from low‐amplitude responses do not match well with those from strong excitations, which arguably are more pertinent to seismic design. In this study, we present a new identification method through which a structure's dynamic characteristics can be extracted using only seismic response (output) signals. In this method, first, the response signals’ spatial time‐frequency distributions are used for blindly identifying the classical mode shapes and the modal coordinate signals. Second, cross‐relations among the modal coordinates are employed to determine the system's natural frequencies and damping ratios on the premise of linear behavior for the system. We use simulated (but realistic) data to verify the method, and also apply it to a real‐life data set to demonstrate its utility. Copyright © 2012 John Wiley & Sons, Ltd.

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

“…The presented results can be compared to those from previous literature works, especially those from previous study,() compared to which frequencies appears to be very consistent, with average deviations of about 4.14 % and 5.97 % for the pre‐NO and NO segments subsets, respectively. This proves again the efficacy of the rFDD algorithm in detecting modal parameters with real earthquake‐induced structural response signals.…”

“…One may notice that the treated subject of identifying modal properties by employing output‐only short duration and nonstationary response time histories with heavy structural damping, such as the ones encountered in real earthquake response records, appears very challenging in the dedicated literature. Moreover, the present method seems to compete with a rather small number of approaches available on the subject, such as, for example, from one study() itself, devoted to the analysis of the Van Nuys building too, and rather recently from previous studies,() in a different context related to wind engineering. Then, the overall investigation globally sets as a contribution on the stated challenging output‐only identification scenario of short duration, nonstationary, and seismic response signals of heavy‐damped structures, where current methods are not well developed yet, as instead it shall be for the widely treated case of long duration, stationary, and output‐only response time histories of lightly damped structures.…”

“…The structure under analysis for the first part of the present numerical validation is a fixed‐base five‐storey shear‐type frame, taken from one study. () Table summarizes stiffness and mass properties for all the floors. As it concerns damping, two different cases are considered: Stiffness proportional damping ( ζ s ); first mode modal damping ratio is set to 0.5 % . Mass proportional damping ( ζ m ); first mode modal damping ratio is set to 10 % . …”

Spatiotemporal video-domain high-fidelity simulation and realistic visualization of full-field dynamic responses of structures by a combination of high-spatial-resolution modal model and video motion manipulations

“…It has been recently established [32][33][34][35][36][37][38][39][40][41] that there is a one-to-one mapping between the modal superposition model and the linear mixture model of the blind source separation (BSS), which can perform output-only modal identification efficiently. Among a family of BSS techniques that are suited for output-only modal identification, the complexity pursuit (CP) algorithm [36] was shown to be efficient and able to identify closely-spaced and highly-damped modes with little expert supervision and parameter adjustments; it is therefore adopted in this study.…”

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

“…2 The adoption of identification input channels coming from exceptional (nonstationary) earthquake-induced structural output response signals has been considered only a few times in the dedicated literature, either in the Time Domain (e.g. in studies [3][4][5][6] ) or in the Frequency Domain (e.g. in works [7][8][9] ).…”