Laying of LWR on Bridges

8/11/2019 Laying of LWR on Bridges

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LWR ON BRIDGES:WORLD SCENARIO

A PROJECT REPORT

BY

1. ANIL PRAKASH-DyCE/Track, E C Rly

2. PAWAN GURAWA-SrDEN/3/BSB, N E Rly

3. BALDEV RAM-SrDEN/Kota, W C Rly

4. REWTI RAMAN ROY-DEN/ADA, S E Rly

COURSE NO. 725SR. PROFESSIONAL COURSE (ADVANCE P-WAY)


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INDEX

SN DESCRIPTION PAGE NO.

Acknowledgement 3

1.0 Introduction 4

2.0 Background 4

3.0 Practice on Indian Railways 6

4.0Technical Requirements &

Constraints

12

5.0 Track Bridge Interaction 15

6.0 World Scenario 20

7.0 Concluding Remarks 32

8.0 References 34


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ACKNOWLEDGEMENT

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ANIL PRAKASH PAWAN GURAWA

BALDEV RAM REWTI RAMAN ROY


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1.0 INTRODUCTION:

Today the LWR is synonymous with modern track. The need for

modernization of railway track has made it inevitable to introduce LWR

as standard practice to achieve better riding quality and better

maintainability of track as well as to ensure SAFETY. On Indian

railways, the installation of LWR has been very encouraging due to the

in-house development of quality track components like rails, sleepers,

fastenings etc. Indian railways has gone in a very big way for putting

LWR/CWR on normal straight track, but has opted LWR/CWR in a very

limited & conservative manner as far as the bridges & curves are

concerned. Since the entire railway lines are dotted with bridges &

curves, where there is compulsion of breaking the continuity of

LWR/CWR; it can easily be appreciated that the full advantage of

LWR/CWR is not being availed by Indian Railways, as of now.

Thus in the above mentioned context, the issue of continuing

LWR/CWR over bridges, assumes a lot of significance. An attempt has

been made in this project report to study the various practices over the

world railways and make some rational recommendations/remarks.

2.0 BACKGROUND:

The dream of jointless track has fascinated track engineers ever

since the first railway was laid. The welding of rails had been started as

early as in 1905; however the commercial welding on any considerable

scale became common only after 1932.During the thirties, the weights

and lengths of standard rail sections varied from 22kg/m to 65kg/m andlengths from 5.5 m to 27 m respectively. The length of welded rail

panels varied from 18 m to 380 m.


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In India in nineteen thirties, the then existing railways like GIP,

BN, NW, EI etc started conducting trials on welded rail joints. From

1947 to 1966, large number of 5 rail panels and 10 rail panels were put

into track.During the year in 1967 Railway board took a policy decision of

making LWR as the standard track structure on trunk routes and main

lines as a part of modernization plan of IR. But as per para 5.6.2 of the

first LWR manual i.e. Manual of instructions on LWR (provisional)

Oct70, in regard to the girder bridges, with unballasted decks, LWR

shall not be continued over girder bridges of single spans

exceeding 13 m or multiple spans of overall length exceeding

18m. On girder bridges, where LWR is laid, the fastenings shall be

rail-free fastenings so that the rail and the girders expand and

contract independently.Nothing much has changed from that time

and as per latest LWR manual provisions the maximum permitted

overall length of girder on which the LWR with 60 kg track in zone

IV can be continued is a bare 11m with rail free fastenings and 23

m with partly box anchored sleepers on girders, that too with

certain additional stipulations.

However, at the corresponding period i.e. in year 1968 1969

the bridges as long as 800m were provided with LWR without an

expansion joint on German Railways. JNR succeeded in using LWR on

bridges continuously with some changes in bridge support

arrangement and adjustments in creep resistance. In the America also,

despite difficulties involved, many railways installed welded rails on

bridges in sixties and seventies. Also in Europe, most of the long

bridges were provided with ballasted decks and LWR was used

extensively on girder bridges.


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3.0 PRACTICE ON INDIAN RAILWAYS:

On Indian Railways, the provisions for LWR on bridges is given

in LWR manual para 4.5.6 & 4.5.7. These paras are discussed as

below

Para -4.5.6:- Bridges with ballasted deck (without

bearing):

There is no restriction for laying of LWR/CWR on ballasted deck

bridges without bearing like slabs, box culverts and arches.

Para4.5.7:- Bridges with/without ballasted deck (with

bearings):

i) LWR/CWR shall not be continued over bridges with overall

length as specified in para 4.5.7.1 for BG and not more than 20 metre

for MG.

ii) Bridges on which LWR/CWR is not permitted/provided shall

be isolated by a minimum length of 36 metre well anchored track on

either side.

Para-4.5.7.1:- (i) Bridges provided with rail-free

fastenings (single span not exceeding 30.5 metre and

having sliding bearings on both ends):

Overall length of the bridge should not exceed the maximum as

provided in Table-1 with following stipulations:-

a) Rail-free fastenings shall be provided throughout the length of the

bridge between abutments.

b) The approach track upto 50m on both sides shall be well anchored

by providing any one of the following:-

i) ST sleepers with elastic fastening.


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ii) PRC sleepers with elastic rail clips with fair T or similar type creep

anchors.

c) The ballast section of approach track upto 50 metre shall be heaped

up to the foot of the rail on the shoulders and kept in well compactedand consolidated condition during the months of extreme summer and

winter.

Table 1

Maximum overall length of bridges permitted on LWR/CWR on BG (In m)

Temperature

Zone

Rail section

used

Rail free fastenings on bridges

with PSC/ST approach sleeper

[Para 4.5.7.1(i)]

60Kg 30I

52Kg/90R 45

60Kg 11II

52Kg/90R 27

60Kg 11III

52Kg/90R 27

60Kg 11IV

52Kg/90R 27

Para-4.5.7.1:- (ii) Bridges provided with rail-free

fastenings and partly box-anchored (with single span

not exceeding 30.5 meter and having sliding bearings at

both ends):

Overall length of the bridge should not exceed the maximum as

provided in Table-2 with following stipulations:-

a) On each span, 4 central sleepers shall be box-anchored with fair V

or similar type creep anchors and the remaining sleepers shall be

provided with rail-free fastenings.

b) The bridge timbers laid on girders shall not be provided with through

notch but shall be notched to accommodate individual rivet heads.


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c) The track structure in the approaches shall be laid and maintained to

the standards as stated in item 4.5.7.1 (i) (b) and (c) above.

d) The girders shall be centralized with reference to the location strips

on the bearing, before laying LWR/CWR.e) The sliding bearings shall be inspected during the months of March

and October each year and cleared of all foreign materials. Lubrication

of the bearings shall be done once in two years.

Table 2

Maximum overall length of bridges permitted on LWR/CWR on BG (In m)

Temperature

Zone

Rail section

used

Rail free fastenings on bridges and

partially box-anchored with PSC/STapproach sleeper [Para 4.5.7.1(ii)]

60Kg 77I

52Kg/90R 90

60Kg 42II

52Kg/90R 58

60Kg 23III

52Kg/90R 43

60Kg 23IV

52Kg/90R 43

Para-4.5.7.1:- (iii):

Welded rails may be provided from pier to pier with rail-free

fastenings and with SEJ on each pier. The rail shall be box-anchored

on four sleepers at the fixed end of the girder if the girder is supported

on rollers on one side and rockers on other side. In case of girder

supported on sliding bearings on both sides, the central portion of the

welded rails over each span shall be box anchored on four sleepers.

See Fig.4.5.7.1 (iii).


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Para-4.5.7.1:- (IV)

LWR/CWR may also be continued over a bridge with the

provision of SEJ at the far end approach of the bridge using rail-free

fastenings over the girder bridge (Fig. 4.5.7.1 (iv)). The length of the

bridge in this case, however, will be restricted by the capacity of the

SEJ to absorb, contraction and creep, if any, of the rails. The length of

the bridges with the above arrangement that can be permitted in

various rail temperature zones for LWR/CWR with SEJs having

maximum movement of 120 mm and 190 mm are as follows:-

Table 3

Max. length of bridge

with SEJ

Initial gap to be

provided at td

Rail temp.

Zone

Max

Movement

of SEJ

used

(mm)

With

ST/PSC

approach

sleepers

With CST-9

approach

sleepers

With

ST/PSC

approach

sleepers

With CST-9

approach

sleepers

IV 190 55m 45m 7.0 cm 6.5 cm

III 190 70m 70m 7.0 cm 6.5 cm

II 190 110m 100m 6.5 cm 6.5 cm

I 190 160m 150m 6.5 cm 6.0 cm

II 120 20m 15m 4.0 cm 4.0 cm

I 120 50m 50m 4.0 cm 4.0 cm

Note : SEJ is to be installed 10m away from the abutment.

Para-4.5.7.1 (v):Welded rails may be provided over a single span bridge with rail

free fastenings and SEJ at 30m away from both abutments. The rail

shall be box anchored on four sleepers at the fixed end of bridge if

bridge is supported on rollers on one side and rockers on other side. In


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case of bridge supported on sliding bearings on both sides, the central

portion of the welded rails shall be box anchored on four sleepers. On

both side of the approaches fully creep anchored fastening shall be

used. The single span bridge permitted temperature zone-wise shall beas under

Table 4

TemperatureZone

Maximum length of single span girder bridge with SEJ(190mm gap) at 30m away from both abutments withfull creep resistant fastening at approaches (td = tm)

IV 75m

III 87m

II 110m

I 146m


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4.0 TECHNICAL REQUIREMENTS & CONSTRAINTS:

If rail free fastening have been provided with LWR on girder

bridges then no thermal interaction takes place between track and

bridge, thereby ensuring that no forces are transferred from girder to

rail or vice-versa due to temperature variation. With such fastenings,

gap at rail fracture becomes limiting factor for providing LWR on bridge.

Thus the limitations for laying of LWR on bridges in IndianRailways are due to certain additional forces on bridges due toLWR/CWR. These forces are

i) Consider bridge with bearing provided with LWR/CWR. Due to free

expansion or contraction of girder, expansion/contraction take placeat free end of bridge and rail on bridge also move with girder as

both are connected to one another either directly or through ballast,

but at approach the movement is restrained by ballast resistance.

Due to this additional forces exerted in rail on bridge, which

transmits to sub structure through girder & bearings.

ii) In addition to above substructure of bridge also over loaded due to

higher tractive & braking forces of modern locomotive & stocks.


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Existing bridges were not

designed by considering above

forces and corresponding rail

stresses. The safe option forproviding LWR/CWR on

bridges is to keep rail & girder

independent of each other, so that there is no interaction of forces

between girder & LWR. This can be achieved by providing rail free

fastenings. In India we have been using dog spike and rail screw as

RFF and now pandrol has come up with a zero longitudinal restraints

design. Under normal circumstances there is small gap between the

base plate and top side of rail foot. In case of large lateral forces, the

baseplate prevents the overturning of the rail. The pad under the rail is

made up of low friction material like Teflon, which provides an almost

zero friction movement between rail & sleeper.

When rail free fasting provided on bridge & fracture occurred on

or near bridge, the gap at fracture will be wider as compared to fracture

in LWR on ordinary formation. This gap is equals to gap due to two

breathing lengths & due to free movement of LWR

g = g1 + g2 + g3

= Gap due to two breathing lengths [g1 & g3] + gap due to freemovement of LWR [g2] over bridge

2

= 2AE (t) + Lot2R

This can be understand by force diagram as shown below-

Force dig. in absence of bridge Force dig. With bridge


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F is the location of fracture. Hence in case of fracture, there will

be additional gap equal to Lot. Maximum length of the bridge in LWR

will, therefore, be restricted so that gap due to fracture can be

traversed by wheel i.e. 50mmwithout derailment, hence 2

2AE (t) + Lot < 502R

Hence value Locan be increased for a particular rail section is to

increase the value of R by compacting ballast at bridge approach,

increase sleeper density to 1660 at bridge approach, heaping of ballast

at bridge approach and box anchoring of sleepers. By doing all this, the

bridge with sliding bearing at both end, rail free fastening throughout

the length, the value of Lorestricted as given in para 4.5.7.1(i).For further increasing the length of bridge with LWR is to

improve approaches as above and provide few sleepers on each span

with creep restraints fastenings at location where the girder movement

is minimum to prevent more gap at fracture. This can be achieved by

providing 4 central sleepers with creep resistant fastenings and

remaining with rail free fastening [with single span not exceeding

30.5m with sliding bearing at both end], bridge timber with notch for

individual sleeper, centralization of girder with reference to location

strip on bearing before laying LWR, inspection of bearing twice in a

year with greasing once in two years. The value of Lo restricted as

given in para 4.5.7.1(ii).

The even longer length of LWR can be provided on bridges by

providing creep resistant fastening at selected locations on bridge, if it

is ensured that:

(i) Gap at fracture is not excessive,

(ii) Rail stresses are within safe limit and

(iii) Structural safety of the bridge is not jeopardized.


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5.0 TRACK BRIDGE INTERACTION (UIC 774 3R)The LWR induces additional thermal forces in the track, Stress

developed due to restraining free expansion/contraction of the Rail

When such type of track is laid on the bridges, two types of Situations

arises-

i) Bridges with ballasted decks without bearing:

LWR can be continued over bridges without bearings like slabs,

box culverts and Arch bridges, where there is no relative movement

between bridge and LWR Track.

ii) Bridges with/without ballasted deck with bearing:

When the bridge structure and the track exhibit relative movement

to each others, then there is interactive effect which is to be taken intoconsideration. Further the interactive effect can be tackled in two

different ways namely-

a) The rails and bridges can be made independent to each other

by providing rail free fastenings, so that movement of rails and bridge

deck are independent and they do not exert force on each other.

b) The rails and bridges are not made Independent and thus both

will exert inter alias forces on each other and the forces thus generatedare calculated and assessed and taken care of, in assessing the

strength of existing bridges and in the case of new bridges, the same

are taken into account at design stage itself. Determination of

interaction effects quantitatively is quite complex.

No reliable method was available for this purpose till UIC

recommendations for calculations of these interaction effects

were issued. To analyze and assess these interactive forces, the

ERRI specialists Committee D 213 has conducted detailed studies and

the results of the same have been published in the form of a report

named UIC774-3R of the year 2001.

Interaction between track and bridge, i.e. the consequence of

the behavior of one on the other, occurs because they are interlinked,


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regardless of whether the track is directly fastened or has a ballasted

bed. The interaction takes the form of the forces in the rails and in the

deck and its bearings, as well as displacements of the various

elements of the bridge and track. If the interaction is within the control,then the bridge will continue to fulfill its functions i.e. supporting the

track, without the track being subject to anomalies.

There are two types of anomaly: The rail fractures or

disruption of the link between track and bridge such that track stability

is no longer guaranteed. Therefore interaction must be taken into

account as a serviceability limit state as regards the bridge as well as

being an ultimate limit state as regards the rail. The acceptable limit

state for the track depends on its design and state of maintenance. The

permissible values used in UIC report are the values that are most

widely permitted for standard track components in a good state of

maintenance. If a railway for its own reasons operates outside the

scope of application, that railway will still be able to use the calculation

methods by replacing criteria given in UIC report with new criteria

based on its own experience and observations. Similarly, the track

strength taken into account and the temperature increase envisaged

were drawn from the knowledge of the various railways. It is perfectly

possible to use this method but with different Values, if the need arises.

It should also be noted that the displacement or rotations to be

checked only concern what has to be checked to guarantee that the

behavior of the bridge cannot damage the track and alter its behavior.

There are other checks to be made as regards displacements and

rotation of the structure, these being concerned with problems of

comfort, dynamic behavior or strength.

5.1 EFFECT OF THE PRESENCE OF BRIDGE IN THE TRACK

Introducing a bridge under a LWR means, effectively, that the

LWR Track is resting on a surface subject to deformation and

movements. Thus causing displacement of the track. Given that both


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track and bridge are able to move, any force or Displacement that acts

on one of them will induce forces in the other. Interaction therefore

takes place between the track and the bridge as follows:

i) Forces applied to a LWR track induce additional forces into the trackand/or into the bearings supporting the deck and movements of the

track and of the deck.

ii) Any movement of the deck induces a movement of the track and an

additional force in the track and, indirectly, in the bridge bearings.

PARAMETERS AFFECTING THE PHENOMENON:A distinction can be made between bridge parameters and track

Parameters.

5.1.1 BRIDGE PARAMETERSa) Expansion lengthb) Span lengthc) Support stiffnessd) Bending stiffness of the decke) Height of the deck

5.1.2 TRACK PARAMETERSa) Track resistanceb) Cross sectional area of the rail

5.2 ACTIONS TO BE TAKEN INTO ACCOUNT

The cases that could lead to interaction effects are those thatcause relative displacements between the track and deck. The casesconcerned are as follows:i) The thermal expansion of the deck only, in the case of LWR or thethermal expansion of the deck and the rail, wherever a rail expansiondevice is present.ii) Horizontal braking and acceleration forcesiii) Rotation of the deck on its supports as a result of the deck bendingunder vertical traffic loadsiv) Deformation of the concrete structure due to creep and shrinkage

v) Longitudinal displacements of the supports under the influence ofthe thermal gradientvi) Deformation of the structure due to the vertical temperaturegradients.

In most of the cases, the first three effects are of majorimportance for the bridge design.


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5.3 PERMISSIBLE ADDITIONAL STRESSES IN CWR ON THEBRIDGE

Theoretical stability calculations, on UIC60 CWR, 90 UTS,

minimum curve radius 1500 m, laid on ballasted track with concrete

sleepers and consolidated >300 mm deep ballast, well consolidated

ballast, give a total possible value for the increase of rail stresses due

to the track/bridge interaction are;

i) The maximum permissible additional compressive rail stress is 72

N/mm2

ii) The maximum permissible additional tensile rail stress is 92 N/mm2.

5.4 ABSOLUTE AND RELATIVE DISPLACEMENT

Limits have to be placed on the displacement of the deck and

track in order to prevent excessive deconsolidation of the ballast. The

displacement limits also play a role in limiting indirectly the additional

longitudinal stress in the rails. These limits are as follows:

i) The maximum permissible displacement between rail and deck or

embankment under braking and/or acceleration forces is 4 mm.

ii) In the case of CWR on ballasted track with expansion devices, the

maximum permissible absolute horizontal displacement of the deck

under the same loads is 30 mm.

5.5 END ROTATION OF THE DECK

The end rotation of a bridge deck due to traffic loads is an

important factor for determining satisfactory track/bridge interaction

behavior. In order to determine an appropriate limit to the end rotation

of a bridge deck it is necessary to consider also other criteria such as

dynamic effects (ballast maintenance) and passenger comfort. Under

vertical loads, the displacements of the upper edge of the deck end

must be limited in order to maintain ballast stability. Obviously, the

effects of this displacement must be added to temperature variation

and of braking/acceleration.


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i) In the case of CWR on ballasted deck, the permissible

displacement between the top of the deck end and the embankment or

between the tops of two consecutive deck ends due to vertical bending

is 8 mm.ii) The maximum vertical diplacement of the upper surface of the

end of a deck relative to the adjacent construction has to be limited.

5.6 SUPPORT REACTION

The interaction results in horizontal support reactions at the

fixed elastic supports, and these must be taken into account along with

conventional support reactions when calculating the structure and

supports.

5.7 RAIL EXPANSION DEVICES

It is preferable to avoid expansion devices in the track, but one

should always be inserted at the free end of the deck if the total

additional rail stress or the displacements exceed the permissible

values. Using the possibility of locating the fixed support at the middle

of the deck, it is possible to increase the length of a single deck

carrying CWR. Generally speaking this will lead to the following

conclusion:

The maximum expansion length of a single deck carrying CWR

without expansion device will be:

i) 60m for steel structures carrying ballasted track

ii) 120m for steel structures deck with fixed bearing in the middle

iii) 90m for structures in concrete or steel with concrete slab

carrying ballasted deck track

iv) 180 m for structures in concrete with fixed bearing in the

middle In the case of unballasted deck, a specific evaluation should be

done. Even when the calculated stresses and displacements do not

exceed the permissible values, it may be necessary to fit an expansion

device in the track. This is the case when the daily variation of the deck


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exceeds the permissible values taking into account the track

maintenance conditions.

The calculations are made using the precise track arrangement

(CWR expansion devices, joints) when, for any reason e.g.Maintenance works consisting of serving CWR, this track arrangement

is modified, the service conditions on the bridge should be reviewed.

The bearings could also be modified and prohibition of braking forces.

A new analysis of the interaction effects should be made, when the

functioning of the bearings and/or of the supports is changed.

5.8 CALCULATIONS USING UIC REPORT

For designing the structure from the point of view of Track /

bridge interaction, three different steps of calculation can be used-

I) Pre- dimensioning method

ii) Calculation without interaction and calculations with

interaction.

iii) Calculations with computer program.

6.0 WORLD SCENARIO:

A literature survey has been done by RDSO to know the

practices being followed on various Railways. The survey reveals that

maximum length of the bridge ( Ballasted and Unballasted) is varying

from Railway to Railway. A summary of the information collected in this

regard is as under :-

(i) Maximum lengths permitted on ballasted track

Type CSD DB JNR SBB SNCF BR NS OBB RENFE SNCB

Steel

structure

- 60 - 25 100 20 15

to

48

Study in

individual

case

Not used

with CWR

No.

limit


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Concrete

structure

No.

limit

120 No.

limit

25 100 20 16

to

53

Study in

individual

case

No. limit No.

limit

Composite

structure

- - - 25 100 20 - Study in

individual

case

This type of

structure

not used

with CWR

No.

limit

(ii) Maximum lengths permitted on unballasted track

Type CSD DB JNR SBB SNCF BR NS OBB RENFE SNCB

Steelstructur2 6220 1t Studyiindivilcase20(forsilspan),tinindivilcase(ultilspan)

No.liitConcretstructur 216220 1t Studyiindivilcase

ThistypestructureuseditCWRNo.liit

Compositstructur 2-6220 -StudyiindivilcaseThistypestructureuseditCWR

No.liitCSD CzechoslovakianRailwayDB GermanRailwayJNR JapaneseNational RailwaySBB SwissRailwaySNCFFrenchRailwayBR BritishRailwayNS NetherlandsRailwayOBB AustrianRailwayRENFESpanishRailwaySNCBBelgianRailway


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It is further revealed from literature that most of the Railways

were not having the theoretical basis regarding the provisions they are

observed. These provisions were adopted just based on their past

experiences.Railways world over have been trying to lay LWR/CWR

continuously over ballasted as well as unballasted decks to fulfill their

long cherished dream of having smooth ride over bridges. To

implement this, they are experimenting with innovative fastening

systems viz. Zero Longitudinal Restraint (ZLR), low toe load elastic

fasteners and also different types of expansion devices to

accommodate expected expansion/contraction. New bridges are now

being designed duly taking into account the LWR forces with/without

expansion devices. For this, computer based models and simulation

techniques have been vastly adopted to simulate LWR forces on

bridges, track/bridge interaction and expansion patterns. Different

railways have adopted different approaches with a single objective in

their mind to lay LWR/CWR over bridges and almost all have achieved

a fairly encouraging degree of success. Some of these approaches are

discussed below:

6.1 GERMAN RAILWAYS (DB)

German Railways have evolved an unique system to avoid

interaction between unballasted steel girder deck and LWR/CWR track.

In this design a solid steel bar with a side groove is welded on top of

the stringers. Over this special bearing plates having jaw are placed

which slide in the groove. Sleepers rest over these bearing plates, the

connection being secured by bolts/sleeper screws. This arrangement

permits relative movement between sleeper and girder. In this design it

is usual to provide a SEJ after 400 m even though on some bridges a

length of 800m was provided without an expansion joint. The main

advantages of this system are:


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i) Track structure on top is unaffected

ii) Need for special fastening is obviated.

iii) The arrangement is much stronger than rail free type againstvertical buckling.

iv) The arrangement maintains very good alignment.

v) No maintenance of anchor bolts/ special fastening is involved.

vi) There is no problem of sleeper seat corrosion.

The main problem with this design is that resistance to creep

being very small; wider gap at rail fracture is to be expected. To

counteract this, USFD testing at increased frequency was employed.

This resulted in timely detection of flaws and also in case of rail

fractures, gaps were found not dangerous.

6.2 BRIDGE ON HIGH SPEED LINE BRUSSELS-LILLE

(JUNCTION FOR PARIS-LONDON)

This bridge is 438 m long consisting of 7 spans, the main span

being 120 m long. The bridge carries two parallel-ballasted tracks with

UIC 60 rails laid on concrete sleepers. Computer modelling with full

continuous CWR track over bridge was done using the computer

program PROLIS20. The complete track and bridge configuration was

modelled in a discrete system consisting of 263 nodes and 416

elements assuming construction symmetry over both the tracks and

interaction forces and displacements were studied. Studies concluded

that the application of expansion devices in high-speed tracks on

bridges, as a means to prevent excessive longitudinal displacements

and forces, is not the best solution due to comfort, safety and

maintenance aspects. Instead a very effective solution is possibly the

use of zero longitudinal restraint (ZLR) fastenings over some lengths of

the track. The calculations, carried out in this respect, show a


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considerable reduction of track displacements, track forces and the

relative sleeper/ballast displacements, the reduction being a function of

the length over which these fastenings are installed. Based on this

conclusion the CWR was designed on the bridge with partly ZLRfastenings but without expansion joints, which even resulted in saving

in investment costs. They recommended that the use of ZLR

fastenings, though not widely accepted yet and the construction

perhaps requiring some further development, should be given more

attention considering the favourable theoretical results achieved.

6.3 DIRECT FIXATION OF TRACK ON THE MISSION

VALLEY WEST LRT EXTENSION

Usually bridges are free to expand and contract at the

abutments and hinges, but attaching the rails directly to the bridge deck

would prohibit normal movement. A new design was adopted based on

this concept that allows longitudinal movement of rails near the hinges

and abutments without forcing the bridge to move with it. However,

some control over the rail movement is required to limit the size of the

gap in the event of a rail fracture. For this, two types of direct fixation

fastener plates (DFFs) were used, i.e.

i) One that allows longitudinal movement of the rail, Zero

Longitudinal Restraint (ZLR) fasteners, and

ii) Another that restraints such longitudinal movement of the

rail Standard Restraint (SR) Fasteners.


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the ability to disperse the angular rotation caused by the stiffening

truss. The 2.3 km long continuous stiffening truss deflects 5.3 m (17

feet) at the center of the bridge. The CWR is designed for such a

flexible support and for the resulting change in grades. In addition, theCWR also has to negotiate, at the bridge ends, significant angular bend

caused by the behaviour of the truss under railway loading. The track

structure was kept independent of the longitudinal forces in the

stringers but had sufficient fixity to maintain the vertical and transverse

constraints of the track against buckling. The expansion assembly

consists of moving telescopic girders mounted on vertical rollers and

restrained by horizontal rollers between the stationary girders.

Longitudinally split rails are mounted on these girders .The construction

work was started in 1992 and completed in 1999 with a maximum

permissible speed of 60 kmph.

6.5.1 BRIEF HISTORY:

The original suspension bridge was constructed in 1966. The

main span is 1012.88 m, the side spans are 483.42 m and the three

backstay spans are approximately 100 m each. One of the unique

features of this bridge is its 2300 m (7472 ft) long truss continuing over

the suspended main, side and backstay spans. This was purposely

done to prevent large break in grade under train loading. The bridge

was built to carry four lanes of highway traffic at the upper deck level

with design provisions for a second phase construction to allow future

railroad track installation at the bottom chord level. In 1992, it was

decided to add two railroad tracks at the lower level and to widen the

upper deck to accommodate six highway lanes with minimum

interruption to the existing traffic.

Various components such as rails, guard/check rails, low toe

load fasteners, slide plates, expansion assembly etc had to be chosen

in a manner to suit the assembly in working as a unit permitting the rail


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movement to the effect and separating the bridge structure from the

LWR/CWR track completely. The system provides for free expansion of

the rail and also isolation of bridge and track from each other.

6.5.2 SELECTION OF THE TRACK

The main considerations of track on a suspension bridge were:

i) Aerodynamically acceptable behaviour

ii) Low dead load

iii) Independence from stresses in truss

iv) Lower noise and maintenance levels

v) Safety during derailment

vi) Capacity to accommodate a large expansion joint at ends CWR with

elastic fasteners on wooden sleepers at 60 cm spacing was found most

suitable to these requirements. The track was designed to UIC

standards. The open deck with all these arrangements was found

suitable from aero dynamical requirements also.


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6.5.3 TRACK LAYOUT ON THE BRIDGEThe track layout on the bridge is divided into different zones on

the 2300 m length of the bridge as follows:

i) standard zone

ii) anchor zone

iii) end zone

iv) expansion zone


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v) creep free zone

The standard zone : It is basically a rail slip zone,

approximately 2150m long and consists of CWR. The track in this zone

can flex to follow the different deflected shapes of the suspended trusswith maximum deflection at center is 5.3 m. The continuous rail can slip

in its chairs longitudinally within the limits of the zone without picking up

the axial forces of the stringer that supports it.

Anchor zone: At either end of the bridge the CWR is terminated

over a short length wherein the rail is anchored to the stringer through

an anchor joint. The anchor joint is a specially designed insulated

connection where in the rail is rigidly connected in the longitudinal

direction but the rail is allowed the usual resilient support. This

connection will provide the uniformity of the track modulus and prevent

uneven wear of the rail.

End Zone This is a short stretch of track between anchor joint

and start of expansion joint complex. Bonded rails at one end and

insulated rail joint at the other end is provided for bypassing the track

circuit over the expansion joint.

Expansion Zone The expansion zone accommodates the

expansion complex. The expansion zone is kept free of CWR forces.

Bonded rail joints are provided at each end for easy replacement of the

expansion joint.

Creep Free Zone In order to protect the expansion zone and

to arrest any possible longitudinal movement, the creep free zone is

provided with extensive creep anchors and an anchor joint at the

approaches.

Tension Clip Mark 3 The rail needs to adjust to the deflection

of the long stiffening truss as the truss will deform under live load which

is effected by slipping of rails longitudinally. A new clip was developed

by modifying the standard SKL-12 clip, which induced a low toe load of

300 kg instead of the standard toe load of 1300 kg. This clip had

additional characteristic of a partial rail free type fastener, which allows


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the rail to slide longitudinally on its chair. As a result, the running rail

stresses remain independent of the rail stringer stresses. To facilitate

such sliding, a 3 mm smooth stainless steel plate is provided

underneath the rail.

6.5.4 EXPANSION ASSEMBLY COMPLEX.

The suspension bridge truss is a flexible structure. The railway

loading consisting of heavy concentrated loads, when moving on this

flexible bridge causes local and global deformation of the truss. The

railway track experiences steep grades and changes of grades at the

center and specifically at the ends of truss. If the running rail is rigidly

fixed to the end stringer, the transition girder will result in a kink in the

rail and high bending and fatigue stresses. Therefore, the rail is

mounted on resilient chairs capable of allowing the rail base to rise and

fall to adjust to the imposed curvature. This has a significant effect at

the end producing an angular bend in the rail. The thermal expansion

of the trusses is significant at the ends. In addition, the truss ends also

move in and out due to deflection of the truss under the live load

depending upon the location of the load. The maximum calculated

movement at the ends for the design was 1500 mm.

After detailed research and studies of various existing systems

the split rail type of expansion joint was developed. The other designs

like switch expansion joint, moving sleeper type etc were not adopted

due to large space requirements at the end of the bridge and more

maintenance requirements due to large number of moving parts.

Considering the limited space available at the end of the bridge, the

telescopic girder type expansion joint was selected as the most

suitable.

The expansion assembly complex so evolved comprised of the

following important components

i) Transition girder and telescopic girders

ii) Split rails for rail expansion


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iii) Check rail and its expansion arrangements

iv) Angular bend dispersion components

v) Telescopic girder mountings

Such expansion system is located at either end of the bridgeand was specially designed to address the requirements such as

a) restricted space, b) high expansion range and c) construction of the

unit under traffic conditions on an existing bridge etc.

The expansion assembly used on this bridge is one of the

largest and most complex expansion assemblies in the world providing

for constant cyclical longitudinal movements and the angular bends in

the running rail.

This expansion joint has been accommodated in a limited space

of 8.5 m thus making it the most compact, yet one of the largest

expansion joints in the world.

In this arrangement to cover the expansion gap of 1500 mm at

the ends and to flex for the angular bend, a short 6.0 m transition girder

was designed. This also acts as the inner moving telescopic girders for

expansion. The moving telescopic girder is inserted between the two

stationary telescopic girders and held laterally and rigidly by two

horizontal rollers with a preload force of 100 t in order to maintain

clearance of 6 mm between stationary and moving girders. These

girders are designed very stiff, structurally, to limit deflection to not

more than 1 mm. On these girders L shaped split rails having top

profile of UIC60 railhead have been used. These split rails are made of

high manganese steel, forged and surface hardened in fine laminated

perlite structure to a level of 1150 N/mm2 for a depth of 25 mm for

wear resistance. In order to control and guide the wheel to roll at the

gauge face, a U69 type high performance rolled steel check rail is

placed at 45 mm clearance. The check rail is kept continuous over the

expansion gap. It is extended continuously from the truss over the

telescopic girder and expansion joint up to the approaches to provide

lateral restraint to the wheel flange. The check rails have been


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provided with an expansion arrangement on the approaches. In order

to uniformly distribute the angular bend of maximum .06 rad and permit

rail to assume a curvature the rail is fixed on special type of chairs. A

dispersion length of 2052 mm was considered sufficient on thetransition girder and similarly on end stringer. The horizontal rollers are

mounted on the stationary girders. The vertical steel rollers on the

bronze bearings are mounted at the bottom of the telescopic girder at

the far end. The steel assemblies in which the rollers are housed are

designed with close tolerance to resist lateral forces and uplift forces

caused by the passage of wheel loads. These rollers are critical in

maintaining gauge and close clearances in the split rail.

7.0 CONCLUDING REMARKS:

From above discussion following conclusions can be made-

1. Maximum length of bridge (ballasted or un-ballasted) over which

LWR can be continued, is varying from railway to railway, probably on

account of the forces considered in the original design of the bridge.

2. On IR, there is no restriction for LWR on ballasted deck bridges

without bearings. Even all the bridges can be provided with LWR with

provision of rail free fastening, partial box anchoring and SEJ on each

pier.

3. There is no restriction on provision of LWR on ballasted deck

bridges as for as Czechoslovakian Railway (CSD), Japanese National

Railway (JNR) and Belgian Railway (SNCB) in case of concrete

structures.

4. Minimum length permitted on bridges with ballasted deck

bridges is NIL in case of Steel structures as in Spanish railway

(RENFE).

5. Maximum length permitted on bridges with un-ballasted deck

bridges is 120 m with concrete structures as in case of German

Railway (DB).


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6. Minimum length permitted on bridges with un-ballasted deck

bridges is NIL in case of Steel as well as concrete structures in

Spanish railway (RENFE) and Belgian railway (SNCB).

7. Most of the Railways are not having theoretical basis regardingthe provisions being observed. These provisions have been adopted

just based on their past experiences.

8. Out of 1,19,724 no of bridges on IR, 99547 no of bridges which

are Arch, slab, pipe or other, are covered under para 4.5.6 and 19,149

nos are covered under para 4.5.7.1 of LWR manual. Thus there are

only 928 nos of bridges that are not covered under provisions of LWR

manual.

9. On IR, 190 mm gap SEJs may be utilized so that LWR manual

can be implemented fully.

10. As existing manual provisions in case of ballasted deck bridges

are with rail free fastening suitable zero longitudinal resistance

fastening (ZLR) to be used on PSC sleeper should be introduced.

11. Case to case study & trials under Indian conditions for all the

existing bridges should be carried out as brought out by the UIC report

no 774-3R for continuing LWR/CWR over the bridges that are not

covered by the LWR manual.

12. Experiments/field trial should be conducted to under stand the

thermal interaction between bridge & track when LWR is provide with

elastic fastening.

13. It is desirable to analyze the forces due to track-bridge

interaction and take into account the same while designing new

bridges.


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8.0 REFERNCES:

(i) Long Welded Rails, 2005 (IRICEN publication).

(ii) UIC Code no 774-3 R, Oct-2001.

(iii) Long welded Rails on Girder bridges by L S Mittal.

(iv) LWR on bridges by H K Jaggi (Article in IPWE Journal).

(v) 7thMeeting of the extraordinary TSC, Oct-2002.

(vi) Improved Knowledge of CWR Track by Coenraad Esveld.

(vii) CWR for Seoul subway no. 2 Dangsan Bridge by ZLR by Lee

Duck Young, Kong Sun Yong, Kwon Soon Sub, Kim Eun.

(viii) Direct Fixation Track on the Mission Valley West LRT extension

by Dane Schiling, P. E. Associate Engineer, Boyle EngineeringCorporation.

(ix) Design of High Speed Track on Long Bridges by Prof .Dr.Ir. C.

Esveld , Professor of Railway Engineering TU Delft University,

Netherlands.

(x) Annual report of RDSO Track Directorate for 2003- 2004.

(xi) Design of Continuous Welded Rail on Suspension Bridge: A

Technical Paper for AREMA by Ranganatha r. Rao and Sudhir

Sanghvi- Parsons Transportation Group.

(xii) Pandrol Rail Free or Zero Longitudinal Restraint System by

Pandrol.com.

(xiii) Manual of Instructions on Long Welded Rails, 1996.

(xiv) RDSO Civil Engg. Report nos 148, 166, 169 & 170.

(xv) Long welded rails on girder bridges- R. Rajamani: P-Way

Bulletin, July-1987.

(xvi) SPC-12, Canadian Pacific railway; April-2000.

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Laying of LWR on Bridges

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