INTRODUCTION

i) Increased transportation capacity due to growth in economy

ii) Strategies adopted by IR to meet the demand

iii) Need for 30 tones axle load corridors

iv) Routes identified for 30 t axle load freight corridors.

DESIGN PARAMETERS FOR 30 T AXLE LOAD.

• The track is divided into following distinct components.

i) Rail

ii) Sleepers

iii) Fastenings

iv) Ballast

v) Formation

RAILSi) Very costly component:: - about 40% of entire track

costii) Most significant bearing on load carrying capacity and

safety.iii) Introduction of new technologies –• high strength rail, • modified rail / wheel profiles, • improved lubrications practices, • improved rail maintenance- rail grinding, • improved bogie type like radial bogies.• New technologies – have made it possible to increase

the permitted rail stresses.

RAIL LOADINGi) Design vertical wheel load – expressed as function of

static wheel load –

P design = Ø x P static Ø=Dimension less impact factor

ii) Assessment of impact factor- • Train speed• Wheel diameter• Vehicle unsprung mass• Track condition (including track modules, Track geometry, joints condition) • Track construction• Vehicle condition

IMPACT FACTOR

• Various methods –

• AREA impact factor

• EISENMANN load distribution

• ORE impact factor – most comprehensive

• ORE impact factor – Ø =1+α’+β’+γ’ Contd..

IMPACT FACTOR Contd..

• α’ – f ( vertical track irregularities, vehicle suspension , vehicle speed)

• β’ - f ( vehicle speed super elevation deficiency of the track, location of centre of gravity of the vehicle)

• γ’ - f( vehicle speed , track condition e.g. age, hanging sleepers, vehicle design and maintenance

DESIGN LATERAL WHEEL LOAD

Depends upon• Curve radius• Vehicle speed• Length of vehicle wheel base & its bogie

configuration.• Rail and wheel profiles• Tracking motion of vehicles in the train consist.• Vehicle dimension and tolerances• Driving practices.

RAIL DESIGN

• Location of maximum rail stress

• Location B,C,D & E – Critical stresses are either longitudinal or vertical

• A – Shear stress due to wheel/rail contact.

ALLOWABLE RAIL BENDING STRESS

• AREA general approach based on yield• DB approach strength of the Rail material• Australian approach - fatigue tests at MRL - based on UTS of rail material. - 0.4 times UTS - independent of residual and temperature stresses. On IR, for LWR track the allowable bending stresses taken

as about 0.29 times UTS. This is quite conservative as compared to the results obtained by MRL.

SMITH DIAGRAM

WHEEL/RAIL CONTACT STRESS CONSIDERATION

• Very important parameter in heavy axle load operation

• Shear stress determined by Hertz theory • Maximum shear stress tmax = 412 Q r• Permissible shear stress (from fatigue

considerations) = 0.3 X tensile strength of rail steel.

• Maximum shear stress occurs at a depth of 4 to 6mm

RAIL STRESS CALCULATION

RAIL STRESSES –140 RE(AREA)

• Weight 69.13 kg/m

• Impact factor – 72%

• Dynamic wheel load - 25.8 t

• Track modulus initial – 183.7 kg/cm/cm

• Track modulus final - 419.17 kg/cm/cm

• Wear of the rail assumed - 5%

• Reduction in I & Z - 10 %

Stresses due to Head (kg/mm2) Foot ( kg/mm2)

1. Vertical load + 16.251 - 13.813

2. Eccentricity of vertical load

- 4.365 - 2.274

3. Twisting of flange force

+ 7.776 + 4.05

4.Lateral deflection under

flange force

+ 4.787 - 9.573

total + 24.448 - 21.61

Permissible stresses 25.25 kg/mm2 Total

Rail wheel contact stresses = 25.19 kg/mm2

RAIL STRESSES FOR 30t AXLE LOAD FOR

DIFFERENT RAIL SECTIONS Rail section Axle load Track

structureMaximum rail stresses

Permissible bending stresses

52 Kg/90 UTS

30 t PSC, 1660 sleepers/Km,Ballast cushion 250

32.15 Kg/mm2

25.25 kg/mm2 (LWR)

60 Kg/ UIC/90 UTS

30 t PSC, 1660 sleepers/Km,Ballast cushion 250

27.70 kg/mm2

140 RE

(AREA)/90 UTS

30 t PSC, 1660 sleepers/Km,Ballast cushion 250

24.45 kg/mm2

SLEEPERS • FACTORS AFFECTING DESIGN

– Effective sleeper support area.– Maximum dynamic load at rail seat.– Ballast/Sleeper contact pressure – Sleeper bending moments – The flexural requirement

EFFECTIVE SUPPORT AREA

• Schramm L= l – g

Approximation L = l

3

Where L: effective length of sleeper support (mm)

I: total sleeper length (mm)

Maximum Rail seat load• The rail weight• The sleeper spacing• The sleeper stiffness characteristics• The track modulus per rail• Pad stiffness• The amount of play between the rail and the sleeper.• The amount of play between the sleeper and the ballast.

• Contu…

Maximum Rail seat load Contd..

• The beam on elastic foundation model

Talbot and Clarke

qr = sk.ymF1

S= Sleeper spacing

K= track modulus

Ym= the maximum rail deflection caused by the interaction of a number of axle loads.

F1 = factor of safety for variation in track support

• The special committee on stresses in Railroad track qr = 0.56s F1.p

qr = 0.5 s k 4.E I xx

Where K= Track modulusE= Young’s modulus of rails steel Ixx = Rail moment of inertiaqr= predicted rail seat load

Area method qr = Df x P

The three adjacent sleeper method qr= .5 P

0.25

MAXIMUM RAIL SEAT LOAD BY DIFFERENT FORMULA

Three Adjacent sleepers method

qr = 0.50 P

BOEF model qr = 0.43 P

AREA Method qr= 0.60 P

ORE method qr = 0.65 P

Ballast /sleeper contact pressure

• BOEF analysis – Pa = qr

B.L.

Where Pa= average contact pressures

qr= maximum rail seat load

B= breadth of sleeper

L= effective length of sleeper under the rail seat

F2 =factor depending upon the sleeper type and

the standard of track maintenance

• AREA FORUMLA – Pa = 2 qr F2

B.L

ORE finding - Flexural rigidity of sleeper secondary

influence on the magnitude of the contact pressure.

- Equivalent uniform pressure distribution In the region under the rail seat.

Sleeper bending moments

• Battelle solution – Mr = qr l – g

2Mr = qr l – g

8Raymond Mc= qr 2 g – l

4

end bound condition

Half the rail seat load is distributed over the sleeper overhang lenght

Flexural requirements of sleepers

• AREA design method

• qr = Ps Df 1 + ØWhere qr = rail seat load

Ps = static wheel load Df = Distribution factor expressed as a percentage of

the wheel load.

Ø = impact factor

RDSO METHOD

• Design features of sleepers for 30 T. axle load

300 280 260

175175 175

251

221

190

End Rail seat Center

Sectional elevation

300 260

3000

1230 540 1230

PLAN

( I )

(I I )

• Load distribution factor 0.55• Dynamic augment 2.5• Centre binding coeff. 0.4• Deign rail seat 20.625 T.• Bending moment at R.S 227.385 T-cm• Bending moment at R.C 88.0765 T,cm• Deign ballast pressure 5.99 kg /cm2 • No. of prestress wire 22 Nos. 3 x 3• Weight of sleeper 366 kg

BALLAST & FORMATION

SUB BALLAST

BLANKETTING

CONCLUSION:

• For meeting the demand of ever increasing freight traffic, Indian Railway need to go for dedicated freight corridor with 30 T or more axle loads.

• The 30 T axle load routes should be designed as a system based on the principles of life cycle costing. The track and rolling stock engineers have to synergize their strategies to arrive at most optimal design of track and rolling stock as the design requirements are conflicting.

• Since, the heavy axle routes will be dedicated freight corridors, we should be liberal in adopting the permissible values for rail bending stresses. As per the recent research in Australia and other countries where heavy haul operation is order of the day, it has been established that the permitted bending stresses can be taken as 0.4 times the tensile strength of rail steel.

• The rail and sleepers have been designed by adopting the current practices on Indian Railway. The rail section 140 RE (AREA) weighing 69.13 kg/m has been found suitable with modified sleeper weighing 366 kg.