Scaling of mode shapes from operational modal analysis using harmonic forces

• Published in: Journal of sound and vibration Vol. 407; pp. 128 - 143
• Main Authors: Brandt, A., Berardengo, M., Manzoni, S., Cigada, A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 27.10.2017; Elsevier Science Ltd
• Subjects: Actuators; Component parts; Coupled modes; Experiments; Harmonic analysis; Harmonic excitation; Harmonic forcing; Modal analysis; Modal identification; Mode scaling; Operational modal analysis; Resonant frequencies; Scaling; Signal processing; Sine waves; Test procedures; Vibration; Signal processing; Mode scaling; Modal identification; Harmonic forcing; Operational modal analysis
• ISSN: 0022-460X; 1095-8568
• DOI: 10.1016/j.jsv.2017.06.033

This paper presents a new method for scaling mode shapes obtained by means of operational modal analysis. The method is capable of scaling mode shapes on any structure, also structures with closely coupled modes, and the method can be used in the presence of ambient vibration from traffic or wind loads, etc. Harmonic excitation can be relatively easily accomplished by using general-purpose actuators, also for force levels necessary for driving large structures such as bridges and highrise buildings. The signal processing necessary for mode shape scaling by the proposed method is simple and the method can easily be implemented in most measurement systems capable of generating a sine wave output. The tests necessary to scale the modes are short compared to typical operational modal analysis test time. The proposed method is thus easy to apply and inexpensive relative to some other methods for scaling mode shapes that are available in literature. Although it is not necessary per se, we propose to excite the structure at, or close to, the eigenfrequencies of the modes to be scaled, since this provides better signal-to-noise ratio in the response sensors, thus permitting the use of smaller actuators. An extensive experimental activity on a real structure was carried out and the results reported demonstrate the feasibility and accuracy of the proposed method. Since the method utilizes harmonic excitation for the mode shape scaling, we propose to call the method OMAH. •New method for scaling mode shapes from operational modal analysis.•Method based on mono-harmonic excitation of the structure with low forces.•Single- and multi-degree-of-freedom scaling procedures.•Extended experimental validation.