A bespoke signal processing algorithm for operational modal testing of post-tensioned steel and concrete beams

The extraction of modal properties is a difficult task, especially when output-only data is measured. The accuracy of the estimation these modal properties is compromised by noisy signals, and signal filtering is required to suppress unwanted frequency content. Care is required to avoid over-filtering of the output data, which can eliminate valid structural frequency content. This paper describes the development of a bespoke signal processing algorithm to extract the modal properties of both simply supported post-tensioned (PT) steel and concrete sections. Dynamic impact testing was conducted on a series of different PT steel and concrete beams. Acceleration time-history data was recorded. This data was subsequently processed. The Fast Fourier Transform (FFT) was applied to the signal to convert into the frequency domain and a bespoke peak-picking algorithm was used to extract the natural frequencies of the beams. A comparison is made between the accuracy of the estimation of the modal properties for filtered and unfiltered data, and a sensitivity analysis of the filtering and peak picking parameters is conducted to determine the effect on the accuracy of the estimation of the modal parameters. The results show the effectiveness of the bespoke algorithm in increasing the accuracy of the estimation of the modal properties as opposed to the raw, unprocessed signals.