Experimental study on track irregularity of straddle-type monorail

As straddle-type monorail systems evolve toward higher operational speeds, steeper gradients, and more diverse structural configurations, the design of guideway beams has become increasingly complex. Surface irregularities on the guideway beams have emerged as major sources of excitation in the vehicle-guideway interaction system, making it imperative to investigate the characteristics of track irregularities specific to straddle-type monorail lines. Although track irregularity profiles can be acquired through field measurements, the large volume of data collected poses challenges for numerical modeling. In current dynamic simulations, irregularities on the running, guidance, and stabilization surfaces are often approximated using standard spectra such as ISO 8608 Class A road profiles or empirical railway spectra, due to the scarcity of high-fidelity measured data. To improve the operational performance of monorail vehicles and to refine the boundary conditions used in dynamic modeling, a field test was conducted on a revenue-service straddle-type monorail line. Dedicated onboard measurement equipment was installed to collect real-world track irregularity data. A full-length spectral analysis of the test line was carried out and compared against U.S. Class 3, 4, 5 and 6 railway spectra and ISO 8608 Class A and B reference levels. The vertical irregularity spectra, along with the lateral irregularities on the guidance and stabilization surfaces, were quantitatively assessed and fitted using numerical methods. Sections with both relatively smooth and rough track profiles were selected for detailed power spectral density (PSD) analysis and spectral fitting. Based on amplitude distributions, the measured spectra were categorized into two quality levels: Class A (excellent) and Class B (poor). Corresponding spectral fitting coefficients were proposed for each category. This study characterizes the spectral features of straddle-type monorail track irregularities and provides critical reference data for the coupled dynamic design and optimization of vehicle-guideway systems.