Acoustic and Dynamic Characteristics of a Complex Urban Turnout Using Fibre-Reinforced Foamed Urethane (FFU) Bearers

Abstract

A special track system used to divert a train to other directions or other tracks is generally called a ‘railway turnout’. A traditional turnout system includes rails, switches, crossings (special track components), steel plates, fasteners, screw spikes, timber bearers, ballast and formation. The wheel/rail contact over the crossing transfer zone has a dip-like shape and can often cause detrimental impact loads on the railway track and its components. The large impact also emits disturbing noises (either impact or ground-borne noise) to railway neighbors.

In a brown-field railway track where an existing aged infrastructure requires renewal or maintenance, some physical constraints and construction complexities may dominate the choice of track forms or certain components. With the difficulty to obtain high-quality timbers, a methodology to replace aged timber bearers in harsh dynamic environments is to adopt a suitable material that could mimic responses and characteristics of timber in both static and dynamic situations. A critical review has suggested a field trial of an alternative material called Fibre-reinforced foamed urethane (FFU) because of its comparable characteristics to timber, high-impact attenuation, high damping property, and longer service life.

After the review of laboratory tests, a field trial of the FFU material has been implemented at an urban turnout junction in RailCorp’s suburban rail network. The effectiveness of such a method has then been evaluated using integrated numerical simulations, axle box acceleration and ride quality data obtained from the calibrated track inspection vehicle “AK Car”, and operational pass-by measurements of noise and vibration. The field trial demonstrates that using the FFU bearers in an urban turnout is effective in retaining the level of impact vibration and passenger ride comfort. It is also found that the FFU material responds to operational actions in a similar manner as timber. The material can well suppress the high-frequency impact vibration at the crossings. However, it is important to note that, in addition to lateral stability consideration, the vertical stiffness transition along the track is recommended in order to mitigate the damage of track components due to rigid body modes of track vibration.