LR55 Frequently Asked Questions
LR55 Track System - Some questions answered
by Lewis Lesley
1.0 Introduction
A full paper setting out all the testing undertaken of the LR55 track system contains much additional information that will amplify these points. In general the perceived weakness of the LR55 track system is the strength of the bonding material which holds the rail in the concrete foundation troughs. In laboratory and field trials two competing bonding materials were tested :
- SIKA PU Grout "KC330"
- ALH PU Grout "System 6"
The SIKA Grout had previously been tested by the University of Calgary, and the tests undertaken in Liverpool replicated and confirmed the Canadian tests. The KC330 grout was used to bond the light rail system in Calgary. The KC330 was subjected to more laboratory testing than the System 6, and the KC330 was used for the Rotherham Bus Station trial, while the System 6 was used at the Alsing Road Supertram trial. Both have similar bonding, mechanical and electrical properties. SIKA have used the KC330 for nearly 40 years in Germany for external bonding of different materials.
In all the failure testing undertaken, the PU bonds held, while the concrete foundation troughs failed in tension. Properly installed either PU grout is more than adequate for the task of holding LR55 rails in concrete troughs.
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2.0 Installing the track
2.1 Rail
2.1.1 Pre-curving
2.1.2 Rail Jointing
2.1.3 Rail destressing
2.1.4 Track Bonds
2.1.5 Axle counters
2.1.6 LR55 joint with other sections
2.1.7 Anti skid treatments
2.1.8 Installation tolerance
2.1.9 Switches and Crossings
2.1.10 Rail grinding
2.1.11 Weld build up
2.1.12 Repairing fractured weld.
2.1.13 Installation line and level
2.1.14 Steel Specification.
2.1.15 Flangeway depth.
2.2 Trough
2.2.1 Trough length
2.2.2 Trough curves
2.2.3 Insitu trough casting
2.2.4 Trough embeddment and sealing
2.2.5 Water Seepage
2.2.6 Road surface drainage
2.2.7 Trough joints
2.2.8 Trough gauging2.3 PU Grout
2.6 Utilities
2.6.1 Discussions
2.6.2 Diversion ?
2.6.3 Trench widths ?
2.6.4 Routines
2.6.5 HMRI Proceedure
2.6.6 Temporary Track passing loop
2.6.7 Powers
2.0 Installing the track
2.1 Rail
2.1.1 Pre-curving
This is a standard proceedure which can be undertaken in many steel shops. The curve is introduced by pulling the rail between three rollers, two on one side of the rail, and the third on the otherside mid way between the other rollers. On each pass the third roller is progressive pushed further between the first two rollers. The LR55 has been factory curved down to 15 m radius, without modification. By notching the inside of the curved rail it would be possible to achieve 11m radius. In any case if transitions are to be included, factory curving is the only way to achieve the required quality and tolerance.
2.1.2 Rail Jointing
The LR55 rail has been satisfactorily flash butt and thermit welded. Thermit have developed the required mould to weld sections together in street. Flash butt welding is also possible in street. Thermit exhibited a LR55 weld on their Railtex Stand in 1997.
2.1.3 Rail destressing
Rails would normally be destressed in the rolling mill before dispatch to customers. "Jim Crow" curved girder tram rails are not normally treated prior to installation. The other question is how to stress rails to compensate for any thermal movements. This can be by laying at the neutral temperature, or applying a slight mechanical tension prior to bonding. The problems associated with rail stress in railways are hardly a problem in street tramways, where the rails are embedded. The PU Grouts tested are more than strong enough to cope with thermal movements associated with the range of temperatures experienced in the UK. Laboratory tests were undertaken between -20°C and 60°C.
2.1.4 Track Bonds
Each rail will normally be continuously welded providing longitudinal electrical conductivity. Cross overs and other point work electrically connects the two rails in in each track and two adjacent tracks. For further assurance, copper bonds can be brazed under the rail head flange or to the side/bottom of the main rail section. Such bonds are commerically available and can be used to provide continuity along each rail and between rails/tracks, and as an insurance against leakage in the case of a weld failure.
2.1.5 Axle counters
In street tramways with operation "on sight", axle counters are not used since tramcars are integral vehicles. Some systems use vehicle detectors, like magnetic loops or proprietory, eg.Philips "VETAG". These are normally installed between the running rails under the centre line of the trams, to make the location on the trams of "beacons" practical.
2.1.6 LR55 joint with other sections
This is achieved by transition rail sections, as was used for the Alsing Road installation in Sheffield. Two patterns have already been prepared LR55/80lb and LR55/bullhead. With CAD and polystyrene patterns all possible combinations of different rail sections are now easy to achieve. The transition would normally be butt welded to the LR55 and then thermit welded to the conventional rail section.
2.1.7 Anti skid treatments
Two different kind of anti skid treatment have been applied to the LR55 installation on the Supertramway in Sheffield. One is based on an aluminium silicate bonded with epoxy resin, the other is carburumdum based. Both have resisted wear equally . In practice the opportunities for motor vehicles to skid on LR55 tracks should be minimised by tram lanes, and by locating road lanes asymmetrically to tram lines where there is mixed operation.
2.1.8 Installation tolerance
This depends partly on the likely level of tram traffic, the nature of the highway pavement and the requirements of the highway authority. The running rails can wear by about 10mm before replacement. If narrow tram wheel are use this would require grinding of the rail head to remove any step edges. The non running side is rolled about 5mm lower than the running side so that the worse case difference across the groove is + or - 5 mm. The concrete foundation trough would normally be laid flush with the highway pavement.
2.1.9 Switches and Crossings
There is a drawing for a 25m radius switch and 1:2.9 crossing in the LR55 profile. Together these two elements can be used to create all the usual point works:
- turnouts
- cross overs
- two track junctions
- diamond crossings.
These are entirely compatable with the LR55 section. With CAD other radii and crossing angles can be easly achieved.
2.1.10 Rail grinding
A standard sliding or oscillating carburundum based grinder will work perfectly adequately on the LR55 section. The only modification may be the need to remove any step edges (see 2.1.8).
2.1.11 Weld build up
The standard rail head weld up technique has been used in Germany for nearly 30 years with rails embedded in KC330. There is no need to remove or replace the PU bonding, as the mass of the rail disperses the heat so that it is below 200°C at the PU bond interface. The rails would then be reground to profile (see 2.1.10)
2.1.12 Repairing fractured weld.
A full investigation of the reason for weld failure would have to be undertaken, eg.
- poor quality original weld
- too much stress in rail (cold weather ?)
The PU grouting would have to be removed for about 1 metre either side of the broken weld. The Thermit mould would be placed under and around the rails. If the original weld was of poor quality, then the rails would have to be pulled together. Otherwise leaving the rails in an unstressed state would ensure that the weld was not over stressed.
2.1.13 Installation line and level
The compacted bedding layer on which the concrete foundation troughs sit is the first alignment requirement. The technique for achieving that is already well established for laying concrete drainage channels in highway pavements. With the concrete foundation troughs installed, the rails pre-welded into long strings would be aligned to line, level and gauge by either:
- precured wedges of PU grout, supporting the rails as the PU liquid grout is injected and then bonding to the wedge pieces, or
- street clamps with integral laser targets, holding the rails to line, level and gauge while the first PU pour is undertaken. When set sufficient to support the weight of the rails, the clamps are removed and a second pour completes the installation.
2.1.14 Steel Specification.
Normally the promoter specifies the steel quality required. There is a VDV tram rail steel spec. which is used for Ri59 and Ri60 profiles. There is also an old BS spec.2.1.15 Flangeway depth.
Q. Why is the flangeway on the LR55 deeper than the British Standard BS 3 tramway rail?
A. It is the same as the EU Ri60 flangeway/groove, 36mm (1 & 7/16 in) wide and 50mm (1 & 15/16in) deep. The logic for this is that it will also accommodate mainline rail wheels, which have wider and deeper flanges than tram/light rail vehicles. In many EU countries there is some sharing of tracks, eg. for the movement of rail freight wagons into city factory sites, using tram tracks, and as at Karlsruhe and Saarbrucken, light rail vehicles run over main line railway tracks (not to mention San Diego), so need wider tyres and deeper flanges to negotiate railway switches and crossings. In the EU this is normally achieved by the use of a hybrid wheel profile, first developed in Frankfurt am Main, where the tyre is 135mm wide (tram 85mm main line 180mm), and the flange is 30mm deep (cv 20 and 40). To allow for rail wear, the groove has to be deeper than the flanges.
The only place in Britain where rail freight wagons shared tramway tracks was Glasgow. Here the unique track gauge of 4ft 7.75in was used, and the rail wagons ran on their flanges along the bottom of the rail groove.
2.2 Trough
2.2.1 Trough length
For drainage channels the usual trough length is 1m. 6 m was chosen for straight tracks to minimise costs. In practice the troughs being manufactured by extrusion and then cut to length, means that any length can be specied. The Rotherham bus station trial installation used three separate troughs; 2.5m, 3.0m and 5.0m without mechanical jointing, with perfect satisfaction. Road drainage channels are not normally mechanically jointed.
For maximum mechanical strength, provided that there are no rail welds co-inciding with trough joints, which could create a hinge, then simply butting the troughs and allowing the PU grout to enter the space between the trough ends and therefore bonding the troughs together should be satisfactory.
If the steel tendons in the troughs are to be used as a "Faraday Cage" then there will need to be an external electrical bonding system between troughs. Alternately a continuous Faraday cage can be laid in the trench prior to the installation of the concrete foundation trounds. This would consist of a lightweight weldmesh folded into a "U" and sat in the bedding layer, and then grouted between the highway pavement and the trough.
With the rails fully insulated from the concrete foundation troughs there will be less stray current paths (in dry weather). In electrical tests, resistivity over 1000Ωkm has been measured. This is over ten times greater than that required by HMRI. Stray currents should not be a problem in normal installations, including switches and crossings.
The longer the trough length, the less ends to settle. In standard highway drainage channels end settlement is not normally a problem. With a continuous rail bonded to and supporting the trough ends this is very unlikely to be a problem. Trough end settlement was not a problem in the Rotherham trial.
2.2.2 Trough curves
The tightest track radius is likely to be 15m. A 20 m radius trough was designed, which would accommodate rail radii between 15m and 25m. A curved trough would however be difficult and expensive to manufacture. A simpler solution will be to use straight troughs with bevelled ends, which would be cut to length according to curve radius. For example 15m radius can be accommodated in 2m long straight troughs. For radii greater than 25m, the length of the troughs would be increased. At 100m radius 6m long troughs can be used laid as tangents.
2.2.3 Insitu trough casting
The only reason to have insitu cast troughs would be for some special structural requirement on site.
2.2.4 Trough embeddment and sealing
This is standard for concrete drainage troughs and exactly the same techiques would be used. The important control is that the bedding layer is properly compacted to a CBR > 3%.
2.2.5 Water Seepage
This is controlled by proper quality control on installation. The trial length in Rotherham Bus Station did not require any seepage control measures after installtion
2.2.6 Road surface drainage
The concrete troughs edges should be flush with the highway pavement. Road surface water normally drains to the side of the carriageway into gullies. Tramway tracks would usually be near the centre of the carriageway.
2.2.7 Trough joints
The Rotherham installation had three joints exposed to traffic, which were instrumented with strain gauges. This was not a problem, even under the heavy and randomly located bus tyres which crossed, scuffed and turned over the installation.
2.2.8 Trough gauging
In a highway pavement that is not failing plastically, there is sufficient lateral strength to resist the movement of troughs, just as there is for drainage channel installations. A simple rustless steel strop on which the troughs sit, will provide adequate gauge restraint on short radius curves if further assurance is necessary.
2.3 PU Grout
Two grouts have been tested:
- SIKA PU Grout "KC330"
- ALH PU Grout "System 6"
and can be recommended for tramway application. SIKA have a full type approval for their PU Grout from Railtrack plc for railway bonding applications. SIKA also has a worldwide system of support and supply.
The only other grout in the market is Edilon "Corkelast" which is sold only as a filler, and has poor electrical resistance qualities.
There are sufficient LR55 tests and others to satisfy that either SIKA or ALH can be used.
2.4 Pre-assembly
It has been normal tramway practice over 100 years for complex layouts, eg. road junctions, to be pre-assembled in the factory to ensure that there is a proper fit prior to shipping to site for final installation.
2.5 Installation Proceedure.
A method statement has been prepared for the installation of the LR55 track system in highway.
2.6 Utilities
2.6.1 Discussions
All the national Utilities were invited to a Seminar held in Sheffield in Sept, 1994 to explain the LR55 system and to inspect the Rotherham Bus Station installation with a 1m wide trench dug underneath to show the shallow track construction and the fact that the track is self supporting over 1 m wide trenches. This was also attended by HMRI ( Kit Holden).
Further in Edinburgh all the utilities were plotted along the proposed tramway and consulted over the use of LR55 tracks. No utility diversions were required but the main gas main at Haymarket would need plating over, as would a 125,000 Volt cable across Leith Walk.
A safe working proceedure was drawn up by HMRI to enable utilities to maintain apparatus while allowing the tramway to continue operation.
2.6.2 Diversion ?
This would be site specific. Only the traffic magnetic loop detectors would be physically obstructed by LR55 tracks and thus need relocation. Inspection pits may need to be moved or modified to fit around LR55 track troughs.
2.6.3 Trench widths ?
The LR55 track has been lab tested over trenches 2m wide and shown to be self supporting. Im is normally wider than most utility trenches and allows for a margin of tolerance during site works.
2.6.4 Routines
Trenches adjacent to tracks would have to be shored like any other trench in the highway. Then there would have to be safe working practice (eg. lookout).
Utilities under a trough ? This would depend on the length. These might be more economically dealt with by digging a parallel trench adjacent to the track and laying a new cable/duct/pipe, unless there is a digless technology eg. removing and replacing the utility in situ.
2.6.5 HMRI Proceedure
See 2.6.1 above.
2.6.6 Temporary Track passing loop
This was invented in 1894 in Liverpool and is widely used on the Continent. It is temporarily installed like model railway track, and sits in the groove with transition rails to a level about 30mm higher than the original tracks. Trams must make this manoevre at slow speed. It would enable one track to be taken temporarily out of use, eg. for replacement as well as utility works.
2.6.7 Powers
These can be included in the Transport & Works Act Order or made by negotiation with the Utilities. Utilities do not usually like to work near other plant, and tramway tracks would be another utility when installed.
(c) Lewis Lesley
14 Feb 2000