Under sleeper pads: field investigation of their role in detrimental impact mitigation

Under sleeper pads (USPs) are the component installed under the concrete sleepers generally to improve railway track resilience. Initial development in Europe, particularly in Austria, has encouraged the adoption of the component around the world. In practice, the component has commonly been used in certain applications, mainly to moderate track stiffness in special locations such as turnouts, crossings, and level crossing. In heavy haul operation, the heavier wagons result in sturdier bogie structures, higher unsprung mass, and then higher level of wheel-rail interaction forces. Accordingly, the application of USPs to mitigate detrimental impact load consequence on track structure is presented in this paper. A field trial aimed at mitigating rail joint impacts using the USPs with a thickness of 10mm and bedding modulus of 0.2 N/mm3 has been conducted in NSW Australia since October 2011. It was found that the track structure and its heavy-duty components were designed to cater heavy load burden of 30t axle load with rail pad stiffness of 800 MN/m (HDPE pads). \u27Big Data\u27, obtained from both the track inspection vehicle and the sensors installed on tracks, demonstrate that track surface quality (top) of the section was improved after the track reconstruction. Fourier analysis results showed that the track surface (or vertical deviation) tends to deform at larger displacement amplitude and resonates at a lower wavelength of track roughness. Interestingly, the operational pass-by vibration measurements show that the resiliency of USPs has resulted in an increased vibration of both rail and sleeper with USPs. Although the studies have found that the sleepers with USPs tend to have lesser flexures, the field data also confirms that a railway track with USPs could experience a large amplitude vibration, especially when excited by a high-frequency impact force. These behaviours imply that the use of USPs to alleviate the impact force onto track substructure is a trade-off measure that could aggravate noise radiation due to track components

Blast Effects on Hyperloop’s Cylindrical Thin-Shell Structures

Super-high-speed guided systems such as hyperloops and MagLev are highly at risk of cyber and physical threats from either natural or man-made hazards. This study thus adopts a nonlinear finite element method to investigate and analyse blast responses of a spatial thin-shell structure formed as an essential part of the Hyperloop tunnelling system. The thin-shell structure is a longitudinal cylindrical tube used in hyperloop rail concepts that will have the capability to carry passenger pods travelling at speeds in excess of 1000 km/h. A robust parametric study has been carried out on a thin-shell metallic cylinder in accordance with experimental results to validate the blast simulation modelling approach. In addition, case studies have been conducted to simulate the effects of varied charge loading (TNT equivalent) of 10 kg, 15 kg and 20 kg. Since the hyperloop system is in its development stages, potential design modifications to adjust the thickness of the thin-shell cylinder are also simulated. Our findings demonstrate that thicker walls of 30 mm yield almost negligible dynamic displacements with lower blast pressures. However, this modification can cause serious ramifications in terms of infrastructure costs. On this ground, venting ports for blast mitigation have been proposed to alter and alleviate blast effects on the tube deformations. The novel insights reveal that increased venting port sizes can significantly increase the impulse deformations of the hyperloop tube but are key in reducing blast pressures within the asset infrastructure. These findings will inform hyperloop engineers about potential design solutions to ensure safety and reliability of future hyperloop rail travels amid the risks and uncertainties of cyber and physical threats

Vibration Attenuation at Rail Joints through under Sleeper Pads

Modern railway tracks require electrification to power the trains and signaling systems to detect near real-time location of trains on railway networks. Such systems require the rail to carry and return the residual electricity back to substation, while enable signals to transfer within a track circuit. This track circuit requires rail jo ints to divide and insulate each loop of the circuit. Such the rail joints often generate impact transient dynamics to track systems. This paper presents the filed investigation into the vibration attenuation characteristic of under sleeper pads (USPs), which are the component installed under the concrete sleepers generally to improve railway track resilience. The field trial is aimed at mitigating rail joint impacts in a heavy haul track under mixed traffics. \u27Big Data\u27, obtained from both the track inspection vehicle and the sensors installed on tracks, demonstrate that track surface quality (top) of the section was improved after the trac k reconstruction. Fourier analysis results showed that the track surface (or vertical deviation) tends to deform at larger dis placement amplitude and resonates at a lower wavelength of track roughness. Interestingly, the operational pass-by vibration measurements show that the USPs has resulted in an increased v ibration of both rail and sleeper with USPs. Although the studies have found that the sleepers with USPs tend to have lesser flexures, the field data also confirms that a railway track with USPs could experience a large amplitude vibration, especially when excited by a high-frequency impact force. These dynamic behaviours imply that the use of soft to moderate USP could p otentially induce dilation of ballast whilst the use of hard USP may reduce sleeper-ballast friction. In the end, these could then w eaken lateral track stability over time

Design of holes and web openings in railway prestressed concrete sleepers

As the crosstie beam in railway track systems, the prestressed concrete sleepers (or railroad ties) are principally designed in order to carry wheel loads from the rails to the ground. Their design takes into account static and dynamic loading conditions. It is evident that prestressed concrete has played a significant role as to maintain the high endurance of the sleepers under low to moderate repeated impact loads. In spite of the most common use of the prestressed concrete sleepers in railway tracks, there have always been many demands from rail engineers to improve serviceability and functionality of concrete sleepers. For example, signalling, fibre optic, equipment cables are often damaged either by ballast corners or by tamping machine. There has been a need to re-design concrete sleeper to cater cables internally so that they would not experience detrimental or harsh environments. Accordingly, this study will investigate the design criteria and effects of holes and web openings on structural capacity of concrete sleepers under rail loading. The modified compression field theory for ultimate strength design of concrete sleepers will be highlighted in this study. The outcome of this study will enable the new design and calculation methods for prestressed concrete sleepers with holes and web opening that practically benefits civil, track and structural engineers in railway industry