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Modal parameters of large civil engineering structures such as Modal Damping Ratios (MDRs) are determined mainly through output-only modal identification. In this paper, MDRs of a double-layer grid were obtained using output-only modal identification. For this purpose, a double-layer grid constructed of a ball-joint system was tested. Through some random tapping on the structure, the acceleration response in multiple locations was measured. The acquired data were processed using output-only modal identification to arrive at MDRs. The MDRs corresponding to the first eight modes of the grid were extracted by five output-only modal identification techniques, namely Enhanced Frequency Domain Decomposition (EFDD), Curve-fit Frequency Domain Decomposition (CFDD), and three different methods of data-driven stochastic subspace identification. To determine the appropriate model order used in SSI methods, sensitivity analysis was carried out and the resulting number of orders was 200. The proper frequency resolution of 1600 was determined to estimate the MDRs of the grid by EFDD and CFDD. The results showed that the MDRs of the grid obtained from different methods were in good agreement with each other. The grid has very low MDRs because the MDRs of the modes measured using different methods varied from 0.06% to 0.11%. [ABSTRACT FROM AUTHOR]

A great number of studies on the vibration of plates subjected to moving loads are available, which are gained by moving force and moving mass modeling frameworks. As a result, evaluating the reliability of the approximate simulation of a moving oscillator problem through moving force/mass would be of interest to engineering applications. Therefore, in this article, transverse vibration of a thin rectangular plate under a traveling mass-spring-damper system is revealed using the eigenfunction expansion method. Both moving force and moving mass modeling approaches are compared with the moving oscillator and various plate fixity cases, and load trajectories are involved to present benchmark solutions. The spring stiffness range, in which the plate response agrees closely with the corresponding moving force/mass analysis, is recommended. The results elucidate that the moving mass can be considerably unrealistic in predicting the contact force of an undamped oscillator. Moreover, errors in the orbiting force/mass simplification of the orbiting oscillator in predicting the resonant conditions of the plate vibration are not negligible. [ABSTRACT FROM AUTHOR]