Blind modal identification of structures from spatially sparse seismic response signals

Abstract

SUMMARY Response‐only identification of civil structures has attracted much attention during recent years, as input excitations are rarely measurable for ambient vibrations. Although various techniques have been developed by which identification can be carried out using ambient responses, these techniques are generally not applicable to non‐stationary excitations that structures experience during moderate‐to‐severe earthquakes. Recently, the authors proposed a new response‐only modal identification method that is applicable to strong shaking data. This new method is highly attractive for cases in which the true input motions are unavailable. For example, when soil–structure interaction effects are non‐negligible, neither the free‐field motions nor the recorded foundation responses 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 low signal‐to‐noise ratios). Thus far, the said method has been only applicable to fully instrumented systems wherein the number of sensors is equal to or greater than the number of active modes. In this study, we offer various improvements, including an extension that enables the treatment of sparsely instrumented systems. Specifically, a cluster‐based underdetermined time–frequency method is employed at judiciously selected auto‐source points to determine the mode shapes. The mode shape matrix identified in this manner is not square, which precludes the use of simple matrix inversion to extract the modal coordinates. As such, natural frequencies and damping ratios are identified from the recovered modal coordinates' time–frequency distributions using a subspace method. Simulated data are used for verifying the proposed identification method. Copyright © 2013 John Wiley & Sons, Ltd.

Responses of a Tall Building with U.S. Code-Type Instrumentation in Tokyo, Japan, to Events before, during, and after the Tohoku Earthquake of 11 March 2011

“…In this section, we present the results of a blind identification method to confirm that significant frequency shifts indeed occurred during the mainshock (Ghahari et al, 2013a(Ghahari et al, , 2014. As its title implies, this method does not require the input excitations to be known.…”

“…The responses used here are recorded during two pre-mainshock events, the mainshock itself, and eleven post-mainshock events, all of which took place between May 9, 2011 and January 2, 2014. Basic spectral analyses and system identification methods (ARX here) are supplemented by moving window analyses and the mode shapes are computed using recently developed blind identification methods (Ghahari, et al, 2013a(Ghahari, et al, ,2014. The latter (more advanced) methods had to be used in order to work with limited data, which for mode shapes provide only two points above the 1 st floor.…”

Computational modeling of a unique tower in Kuwait for structural health monitoring: Numerical investigations

“…BSS aims to recover statistically independent source signals from the recorded data, which has proven to be a successful approach for modal identification given output‐only measurements of structural systems. () Consider a s ‐DOF time‐invariant linear system with the equation of motion given by where , , and are the system's displacement, velocity, and acceleration responses; , , and are the mass, damping, and stiffness matrices; and is the input. The system response (e.g., the acceleration ) can be expressed in the modal space through modal expansion , where is the modal transformation matrix consisting of real‐valued mode shapes and is the modal acceleration response in the modal space.…”

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

“…In the field of Operational Modal Analysis (OMA), some researchers have investigated the use of strong ground motions in the Time Domain, as for instance. () Rather, the output‐only analysis in the Frequency Domain looks quite shortfall in the earthquake engineering range, especially as concerning to nonparametric algorithms (as Frequency Domain Decomposition (FDD) is). Few notable exceptions come from previous studies.…”