Turnouts for the Taipei - Kaohsiung high speed line have been developed using kinematic gauge optimisation to improve ride quality when diverging at higher speeds. Better design should help to reduce wear and improve life-cycle performance

Johannes Rohlmann
was Project Manager for Taiwan High Speed Railways and is now Managing Director, WBN Wisselbouw Nederland.

Josef Heß
Head of Technolgy Development & Slab Track, BWG GmbH

RAISING TRAIN speeds above 200 km/h on conventional track results in higher maintenance costs for turnouts and rail expansion joints. Studies and research projects led to the development of a new generation of turnouts and expansion joints with geometric design features suited for ballasted or ballastless track (p225). These were specified for use on the Taipei - Kaohsiung high speed line in Taiwan.

BWG supplied 147 main line switches for the project. Of these 120 are installed on the Rheda 2000 ballastless station track (p218), and the rest on ballasted track in the southern rolling stock depot at Tsoying in Kaohsiung (Table I). BWG also supplied expansion joints for the 410 m long steel bridge structures just south of Taichung station. All rail, including turnouts and plain track, employs the JIS60 section used on Japanese Shinkansen slab track.

To oversee preassembly, logistics and installation, and to provide technical advice and documentation, BWG, Pfleiderer Infrastruktur GmbH (now Rail.One) and Eichholz AG formed a joint venture known as Taiwan Track Consultants. During the busiest phases, up to 55 experienced trackwork engineers were working for TTC JV, supervising work at up to 12 separate construction sites simultaneously.

Supply and delivery challenges

All turnout and rail expansion joints were produced, tested and approved in Germany, and then dismantled for shipment to Taiwan. The turnouts were re-assembled at the China Steel Machinery Corp premises in Kaohsiung, with Taiwanese technicians working on up to six assembly benches preassembling switch yokes, blade units, intermediate pieces and crossing units.

Following acceptance by the customer, the assemblies were temporarily stored pending just-in-time delivery to suit construction schedules. Modules up to 55 m long weighing as much as 50 tonnes were transported by road for distances of up to 300 km. Taiwanese logistics company Sea & Land developed a special road trailer for the largest assemblies. All routes had to be assessed in advance, and obstacles such as walls and traffic lights removed temporarily to allow for the passage of the vehicle. Special permits had to be obtained to carry out these movements at night to ensure that the material was available on-site for the next morning.

At some locations, soft ground requried extensive earth-moving work so that the transporter could reach the worksite. Special equipment was developed in Germany to unload the individual parts and manoeuvre them onto site. In some places two 200 tonne cranes were needed to lift the largest and heaviest switch units onto the viaducts under the supervision of TTC staff.

Installation and alignment

Working with the other TTC partners, Eichholz developed a technique to make the installation of preassembled switches more efficient. The Turnout Shifting System allowed a quick initial alignment of switch assemblies to an accuracy of ±5 mm in both horizontal and vertical directions. A modular temporary track allowed the switch components to be transported along the line from unloading site to final position - in some cases as much as 1·5 km. In other cases assemblies were moved along the newly-installed running rails. By the end of the project, nine TSS units were in use along the route.

Measuring and final alignment of the switch modules was completed using an electronic system developed for high speed lines in Germany. This was also used to survey all 75 km of Rheda 2000 track. The final co-ordinates of each switch were analysed using a manually-operated measuring vehicle, and all alignment data logged.

A second check was undertaken before the start of concreting, and only if all criteria were met were the relevant switches and rail section released for final installation.

This project was the first time that many of the local subcontractors had been involved in the construction of ballastless track. One crucial procedure was the final concreting. The entire turnout, plus two or three base segments to each side, had to be concreted together during a single night. For crossover tracks formed of two switches with a radius of 1 200 m, the entire connecting section between the blades on both tracks had to be concreted together. This required about 600 m³ of concrete, which was supplied to the viaduct by up to four pumps. Due to high ambient temperatures, this work could only be carried out at night, and all concreting had to be completed by 05.00 at the latest. To prevent any shifting of the switches caused by rail expansion during the day, the spindles and track fastenings had to be loosened during or immediately after the concreting work.

Seamless track

Another demanding task was the production of continuous welded rail across the transitions between the Rheda 2000 and J-slab trackwork. This required extensive discussions between all partners and detailed calculations. The Japanese trackwork and fastening system has a considerably lower sliding resistance than the Rheda design. The two also differ as regards the contact point flexibility and stability of position.

The first welds to create 200 m rail strings were done using stationary flash butt-welding machines. The final in-situ welds between the rail strings and turnouts used an alumino-thermic process.

Welding companies from Germany, Japan and Taiwan produced approximately 3 800 alumino-thermic welds in just four months, connecting up 58 km of track and 78 switches. Once again, most of this work was carried out at night to avoid the high rail temperatures during daytime.

If the rail temperatures dropped below the neutral temperature of 34°C, the rail sections were pre-stressed hydraulically before welding, over a maximum distance of 600 m.

A process developed by Elektro-Thermit and the Japanese gas pressure welding technique were both used for post-heat treatment of the welded joints in the head-hardened rails.

Works trains and commissioning

As the project progressed, it became necessary for work trains to use the completed track. Specially-trained TTC JV staff were deployed to install switch locks, minising the risk of having trains moving through a construction site. BWG was subsequently contracted to install the switch locks and prepare the track.

Commissioning of the first section of line to act as a test track was undertaken by BWG specialists as well as TTC JV engineers to ensure that this crucial final phase was carried out properly. After the signalling control of the switches was commissioned, the test track was cleared for trial running at 330 km/h. These test runs were also accompanied and evaluated by BWG and TTC JV engineers.

Further test running, culminating in the launch of revenue services in January, confirmed that a German ballastless trackform and BWG's advanced switch design are fully compatible with the Japanese-built Shinkansen trains.

Kinematic turnout design to optimise performance

TO ENHANCE ride comfort through the diverging side of a switch, BWG's new high speed turnout design uses a non-constant radius. To reduce jerking at the transition from the straight rail to the curve, the switch blade is modified by the inclusion of clothoid sections, whereby the initial radius reduces continuously towards the final switch radius.

At the outer end of the divergence, another clothoid section increases from the switch radius to infinity. The end of this clothoid is positioned at half the standard track spacing, so that two identical turnouts can be paired to form a crossover. If the track spacing is greater than 4 m, a straight section can easily be interposed as the clothoids end at infinity. This design reduces the maximum jerk at the start of the turnout to 1 m/s³, ensuring a good ride quality and improved tangential stability.

In normal running, a wheelset follows a sinusoidal path along the rails. When entering a conventional turnout, the sinusoidal pattern is disturbed by deviating contact conditions. The axle is forced into an inclined position, which results in increased wear as the flange strikes the blade and stock rails. In order to eliminate this disturbance, BWG used kinematic gauge optimisation to improve switch geometry. Constructive widening of the stock rails allows the contact radii of the wheel to effect a sinusoidal and undisturbed run over the switch blade. In addition, the cross-section of the blade can be increased, reducing wear on the stock rail, and the blade tips are reinforced (Fig 1). This ensures that geometric contact conditions, rather than the flange, direct the passage of the wheelset through the divergence.

Absorbing vibrations

Elastic ribbed baseplates are used to isolate the static and dynamic wheel loadings on the rail from the sleepers and ballast or ballastless substructure. These baseplates consist of flexible elastomer springs installed so that the ribbed plates are uncoupled from the sleepers. The limit criterion for the flexibility of the springs is the maximum permissible tensile bending stress in the switch components.

From a technical viewpoint, the aim is for the rails to deflect as much as possible in order to attain a long elastic curve. By optimising the design of the springs, the rigidity at the contact points can be adjusted to suit the ribbed baseplates and the bending strength of the rails. This ensures a near-uniform rail flexibility along the entire switch, distributing the wheel load across a large number of bearing points and reducing the static load on any individual sleeper.

Unlike conventional switch mechanisms, VAE's HRS Locking System uses a lift-roll-lower-lock mechanism which ensures a firm interlocking of the blade and stock rail while holding the blade against the slide plates. The stock rail, blade and slide plates form a unit through which the load and guiding forces are distributed.

Because the slide plates of the inner stock rail fastening divert the vertical wheel load from the blade onto the stock rail base, this prevents any horizontal shifting of the blade, as may occur in conventional switches when the wheel load rests solely on the blade.

In the crossing, the rails are connected by a frog tie, which presses the nose against the slide plates. This force is applied continuously and is only released hydraulically when the swing nose must be moved. Again, the slide plates, wing rails and crossing nose form a unit through which wheel loads and guide forces are distributed evenly.

To ensure smooth operation, the the slide plates are coated with molybdenum. The HRS lock in the spring-mounted crossing is also equipped with self-lubricating rollers.

All turnouts are equipped with VAE's Roadmaster monitoring system, which continuously records the turnout forces, the position of the switch blades and swing nose, the minimum clearance between the blade tongue and stock rail, plus the temperature and stresses in the rails. Data from the various turnouts is analysed centrally to support a preventative maintenance strategy.

Turnout sleepers for slab track

A suite of turnouts for Rheda 2000 slab track was developed by BWG in conjunction with Rail.One. This required adjustment of the switches to suit the the depth of the plain line trackform. At the heart of this work was a new design of concrete turnout sleeper (Fig 2).

Adjusting devices are integrated into the switch to allow exact vertical alignment of the turnout rails during installation. After the switch has been aligned horizontally, the switch rails are secured at the correct height and secured by a reinforced concrete infill.

The switches are designed for factory assembly, to permit adjustment and testing before delivery. Sleepers more than 3 m long are produced in two sections (Fig 3), to simplify transport to site by rail or road. These divided sleepers are connected by steel plates to ensure that all components remain properly aligned during final installation.

Rail expansion joints

In contrast to conventional rail expansion joints, the high speed joints developed by BWG concentrate the longitudinal movement onto the stock rail rather than the blade. This means that the horizontal geometry of the stock rail corresponds to an elastic deflection curve, and ensures a constant gauge is maintained in all conditions. The blades and stock rails are secured with special fastenings that provide horizontal guidance and vertical adjustment. Plastic pads with specific friction coefficients cater for different slipping resistances on the blades and stock rails.

The design of expansion joints for major bridges varies to suit the elongation length. For up to ±150 mm (SA-300), the joint can be bridged with filled section rails or standard rails with increased inertia. Where elongation is ±300 mm (SA-600), auxiliary sleepers are centred under the joint and secured by means of a shear construction. Under certain conditions it is necessary to use anchor clamps with reduced slipping resistance, or special contact points catering for increased loads and lifting forces that might occur as a consequence of torsion and offset at the bridge joint.