A proof-of-concept study on a proposed ambient-vibration-based approach to extract pseudo-free-vibration response. (1st June 2020)

• Record Type: Journal Article
• Authors: Moghadam, Amin; Melhem, Hani G.; Esmaeily, Asad
• Is Part Of: Engineering structures. Volume 212(2020)
• Publication Date: 2020-06-01
• Subjects: Damage detection -- Ambient-vibration-based approach -- Fundamental frequency -- Pseudo-free-vibration response -- Frequency-domain; Structural engineering -- Periodicals; Structural analysis (Engineering) -- Periodicals; Construction, Technique de la -- Périodiques; Génie parasismique -- Périodiques; Pression du vent -- Périodiques; Earthquake engineering; Structural engineering; Wind-pressure; Periodicals; 624.105
• DOI: 10.1016/j.engstruct.2020.110517
• Languages: English
• ISSNs: 0141-0296

Abstract

Highlights: This random-vibration-based approach extracts a structure free-vibration response. Two steel frames with different stiffness are tested and numerically modeled. The structure may subject to any ambient vibration regardless of the excitation. Reduction in the structure stiffness causes a decrease of fundamental frequencies. Fundamental frequency is the same under different vibrations for constant stiffness. Detecting a reduction of the fundamental frequency can be an indication of damage. Forced vibration and the use of complex equipment and instrumentation are not needed. Abstract: This paper reports the results of an analytical, experimental and a numerical study (proof of concept study) on a proposed method for extracting the pseudo-free-vibration response of a structure using ambient vibration, usually of a random nature, as a source of excitation to detect any change in the dynamic properties of a structure that may be caused by damage. The structural response contains not only a random component but also a component reflecting the dynamic properties of the structure, comparable to the free vibration for a given initial condition. Structural response to the arbitrary excitation is recorded by one or several accelerometers with a desired data-collection frequency and resolution. The free-vibration response of the structure is then extracted from this data by removing the random component of the response by the method proposed in the paper. The features of the free-vibration response of the structure extracted by a suitable method, namely FFT in this study, can be used for change detection. Possible change of the pattern of these features is dominantly linked to the change in dynamic properties of the system, caused by possible damage. To show the applicability of the concept, besides an analytical verification using Newmark's linear acceleration method, two steel portal frames with different flexural stiffness were made in the steel workshop of the structural laboratory for an experimental study. These structures were also numerically modeled using a finite element software. A wireless accelerometer with a sampling frequency rate of 2046 Hz was affixed on the top of the physical structure, at the same location where the acceleration was recorded for the corresponding numerical model. The physical structure was excited manually by an arbitrary hit and the response of the structure to this excitation, in terms of the acceleration on the top of the structure, was recorded. The pseudo-free-vibration response was extracted and transferred into frequency domain using FFT. The frequency with the largest magnitude which is the fundamental frequency of the structure was traced. This was repeated for several independent excitations and the fundamental frequencies were observed to be the same, showing that the process can correctly identify the natural frequencies of the structure. Similarly, the numerical model was excited and for several base excitation cases, the fundamental frequencies were found to be the same. Considering the acceptable accuracy of the results from the two numerical models in simulating the response of their corresponding physical models, additional numerical models were analyzed to show the consistency and applicability of the proposed method for a range of flexural stiffness. The results confirm that the proposed method can precisely extract the pseudo-free-vibration response of the structures and detect the structural frequencies regardless of the excitation. The fundamental frequency is tied to the stiffness and a larger stiffness leads to a higher frequency, as expected, regardless of the simulated ambient excitation.