Modal mass estimation from output-only data using oscillator assembly

A novel single degree of freedom method is proposed to identify the modal mass or mode shape scaling of an isolated vibration mode from output-only data, using the response of the system coupled with an oscillator which can be very small in comparison. The expedient is considerably simpler than some alternatives requiring controlled input, and no prior assumption is required concerning the unknown parameter, but the frequency of the mode must be known in advance. Two proof-of-concept algorithms were developed for testing the method: a frequency domain peak picking algorithm for lightly damped systems and a time domain one that can take heavy damping into account. Tests were performed on a laboratory set-up and on a real lively footbridge (with and oscillator mass around 1% of the modal mass), assessing the viability of the method and its suitability for real applications.

► The mass or scale of a vibration mode is found by attaching an oscillating mass. ► Two algorithms are proposed to extract this information from free response. ► Tests were performed on a laboratory set-up and a footbridge.