Analysis of loading frequency in flexible pavement using fast fourier transform

Accurate calculation of traffic loading frequency plays a major role in mechanistic design of flexible pavements. Previous studies have highlighted the need for a paradigm shift in determining frequency through frequency domain analysis rather than conventional time domain-based methods. However, limited studies have experimentally investigated the impact of contributing factors including response type, depth and vehicle speed on calculated frequencies in frequency domain approach. This paper presents the results of controlled vehicle testing that focused on frequency analysis of in-situ measured pulses using Fast Fourier Transform (FFT). The tests were conducted in the Integrated Road Research Facility (IRRF) in Edmonton, Alberta, Canada. Longitudinal, transverse and vertical strains at the bottom of the Hot Mix Asphalt (HMA), as well as the vertical stresses recorded at different depths within unbound layers, were taken into account for this purpose. This study showed that dominant frequencies associated with longitudinal strain were the highest amongst those of other considered responses. Besides, the impact of speed and depths on obtained frequencies were clearly reflected. Finally, comparisons were made between the accuracy of HMA dynamic modulus prediction when using FFT-calculated frequency versus using of four well-established frequency calculation methods in time domain. © Chinese Society of Pavement Engineering.