Experimental Characterization and Numerical Assessment of the LONGASF Asphalt-Supported Ballastless Railway Track System

The LONGASF ballastless track system combines longitudinal WZA concrete sleepers, an asphalt supporting layer, and the ICOSTRUN-03 fastening system. Although selected elements of the concept and preliminary numerical models have been reported previously, this paper presents, for the first time, the experimental characterization of the fastening system and an integrated assessment of the track response under vertical, transverse, and longitudinal loading. Laboratory tests were conducted to determine vertical stiffness, longitudinal and transverse rail resistance, and performance under repeated loading, including dynamic rail and sleeper displacement measurements. The experimentally identified parameters were subsequently implemented in simplified dynamic models and three-dimensional finite element models. After repeated loading, changes in longitudinal rail resistance and vertical stiffness remained within the limits adopted in the experimental programme. The numerical analyses demonstrated a strong dependence of track response on foundation stiffness and model extent. In the extended three-dimensional model, the maximum calculated horizontal and vertical displacements were 2.439 and 2.434 mm, respectively, for the weakest foundation condition considered. The simplified dynamic model indicated that sleeper acceleration may exceed the adopted 1 g criterion at the highest analysed speeds. However, because the model did not include vehicle inertia or coupled wheel–rail interaction, 250 km/h should be regarded solely as a parametric calculation case rather than a validated operating speed. The results provide a preliminary numerical assessment of the LONGASF concept and identify asphalt temperature sensitivity, foundation stiffness, fastening-system optimization, and full-scale model validation as key areas for further research.