Implication of 30 Ton Axel Loads PDF
Implication of 30 Ton Axel Loads PDF
Implication of 30 Ton Axel Loads PDF
1.0 INTRODUCTION:
1.1 General
The Indian economy enters the tenth plan with an expectation of 6% to 7% annual
growth in the GDP and consequently 7.2% to 8.0% growth in the transport sector.
These expectations place heavy demands on the already saturated road and rail
transport system which coupled with the inadequacies in the power sector could be a
major constraint in the realisation of the projected economic growth. With Airways,
Coastal Shipping and Inland Waterways being in the fringes, freight transport in
India is basically shared between Road and the Rail sectors. The road network in
India has grown from 4-lakh km. in 1951 to over 30-lakh km now – second largest
in the world.
Post independence the Railways made a flying start almost doubling the transport
output in the first 5 year Plan. There was however a perceptible slowing down from
1968 to 1980 followed by a revival in the last two decades.
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1.3 Comparative Evaluation of Indian
Railways with advanced Railways;
THE world's heaviest and longest freight train runs in Australia. With a payload of
82,000 tonnes and gross load of 99,734 tonnes, the train is formed of 682 wagons,
hauled by eight 6000 HP diesel locomotives.
The 7.2- km train transfers minerals in bulk from one part of Australia to another
crossing thousands of miles of largely uninhabited and desert areas. Theoretically,
just 18 such trains are enough to carry the entire volume of about 1.5 million tonnes
of freight moved every day by the Indian Railways, which deploys 5,000 trains of
varying capacities to do the job.
A comparison of the Railway Systems in China and India makes interesting study.
In the decade 1992 to 2002 the route Km on the Chinese Railways (CR) has grown
from minus 6% to plus 14% in comparison to that of the Indian Railways (IR). The
two Railways carried almost the same volume of Passenger Traffic both in 1992 as
well as 2002. However, in respect of Freight Traffic, the volume carried by CR is
four and a half times that of India. They have achieved these results through more
efficient exploitation of track, locomotives and wagons, and by assigning lower
priority to passenger services. China has a larger proportion of double line and has
adopted automatic signalling more aggressively than India. As a result, CR operates
roughly twice the number of trains on electrified double line tracks than the Indian
Railways
The Chinese Railways are planning an investment of US $ 200 billion in the mega
plan period from 2004 to 2020, basically aimed at network expansion, doubling and
creation of dedicated Passenger and Freight Corridors. .
1. 4
Integrated Railway M odernisation Plan (2005-10) has been made which has
objective to enhance capacity, improve rail-port connectivity, higher axle load
wagons to carry bulk material and development of dedicated freight corridors, two
intercity, corridors Delhi-Patna-Howarh and Delhi – Channai to be developed to run
150 Kmph trains using latest technology high speed coaches
And running of freight train @100Kmph on the high density Golden Quadrilateral
and its diagonals connecting the four metropolitan cities.
At present predominantly running axle load on Indian railway system is 20.32
tonnes are operating. Heavier axle Loads will enable carrying more payload in one
train, which in turn improve throughput substantially.
Hence before a Heavier axle load is permitted to run, the safety of infrastructures has
to be ensured as it carries passenger traffic also.
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Introduction of wagons, which can carry increased loads, is one of the answers
policy makers would look to. Integrated M odernisation Plan (2005-10) released by
Railway envisages running freight trains with axle load of 22.9 t on selected routes.
As a precursor to the ensuring heavier axle loads, Railway Board has taken decision
to run BOXN wagons with CC+8+2 loading on iron ore routes. This would result in
axle loads of the order 22.82t and TLD of 8.51t/m.
In this scenario, introduction of trains with 30t axle loads probably is not quite far
away. Incidentally, 30t axle loading happens to be heavy mineral loading standard.
Running of such heavy axle load trains on the existing track would cause very high
stresses on the track structure which would have far reaching implications on the
requirements of track components and their maintenance and life.
The axle loads running on the Heavy Haul routes of American, Australian, china and
other advance Railways are ranging from 30t to 40 t. However there is major
difference in Scenario prevailing on Indian Railway as unlike the World Railways
where Heavy haul freight trains run on a dedicated Heavy Haul lines, in Indian
Railway same infrastructure has to carry both goods and passengers traffic. Golden
Quadrilateral and its two diagonals constituting 16% of Route Km (25% of running
track Km) carry 55% of passenger and 65% of Freight traffic of the I.R. and are
saturated on most lengths.
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An attempt has been made in this paper to compute the stresses that would be
induced in Rail, Sleeper, Ballast and Formation due to introduction of 30 t axle loads
and the suitability or other wise of these components. M inimum track structure for
running of these heavier loads and its impact on maintenance of P.Way is also dealt
with. Implications for running 30 Tonnes axle load on dedicated freight corridor of
Indian Railways and solutions to overcome the problems are also dealt with.
The Freight Corridors should be constructed with the capability of carrying 30ton
axle load Wagons (currently axle loads are limited to 20.3tonnes) in train formations
of over 14,000t (presently train loads are about 4800 tonnes) hauled by multiple
units of 4,000 to 6,000 H.P. ac/ac high tractive effort modern freight locomotives at
speeds of 100 kmph. The loop lengths should be 1500 meters or longer to permit
accommodation and crossing of train lengths of 120 wagons.
While identification of Freight Corridors could be a matter of a detailed survey, the
basic matrix could comprise:
Connecting Collieries in Eastern and Central India with Power Houses in Northern
and Western India.
Connecting Iron Ore M ines with the Steel Plants. For example Bailladila, Dalli
Rajhara-Bhilai Link and connection to Ports for Export.
Connecting Ports of Western India with the focal point in Northern India for
movement of double stack container traffic.
At present Indian railway has taken up the project of running 30 tonne axle axle load
between Deitari to Banaspani for a distance of 150 Km, which is a dedicated iron
ore route in East Coast Railway.
Fewer wagons will be needed to haul the same load, leading to lower capital cost
and possible reduction in wagon maintenance cost, fewer locomotives, lower fuel
consumption per net tonne, reduction in train wagon kilometre operated, and fewer
crew deployment entailing savings in wages. The railways in North America,
Australia, South America, South Africa and Sweden have all increased axle loads to
obtain significant savings in operating cost. These savings have been achieved
despite increased cost of maintaining tracks, greater track component damages and
shorter component lives.
The raising of the axle load from 22.5 tonnes to 30.5 tonnes yielded 40 per cent
savings in transportation cost in the US. This in turn helped the railways in that
country achieve significant reduction in operational cost of transporting containers
and introducing customised wagons to win back traffic from the roadways.
Boosting wagon productivity, that is, how to carry more per wagon, or how to
achieve higher payload per wagon, has become important for the Indian Railways in
view of the increasing threat from the various other modes of transport, particularly
roadways. Overall, the Railways now accounts for 38 per cent of the country's total
freight movement compared to more than 80 per cent half a century ago. An analysis
of the commodity-wise market share shows that between 1991-92 and 2000-01,
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there was a sharp drop in the rail coefficient for cement, POL, food grains and iron
steel while it improved for coal, iron ore and fertilisers.
Also, while the drop has been significant, not so the extent of improvement. But,
then, the lower axle load presents only one problem. There are several other
problems that need to be tackled along with the raising of the average axle load.
Thus, along with higher axle load, the track load density, that is, the maximum load
permissible per metre length of track (TLD), too has to be increased. Any increase in
axle load without corresponding increase in TLD will have a marginal effect on the
throughput.
The other issues that also deserve careful consideration in this connection are track
friendly bogies, smaller wheel size, and enhancement of maximum moving
dimensions (MM D).
On Indian Railway the strength of the for running various locomotives and rolling
stocks at different speeds is assessed by calculating rail stresses induced
locomotives/rolling stocks running at contemplated speed, using Civil Engg. Report
No.C-100 rail wheel contact stresses on straight and curved tracks due to axle
load combined stresses in rail head, foot, assuming rail wear of 5% are calculated on
52Kg rail and 60 K g rail.
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Permissible Stresses 72 UTS 90UTS
19.25 (LWR) 25.25 (LWR)
It can be seen from the above that even in 60 kg Rail stresses are higher than the
permissible limit, in other words 60 kg 90 UTS Rail also not fit for 30 t axle loads.
The contact between rail and wheel flange should be theoretically a point. Hertz
theory explains that in practice the elastic deformation under higher axle lad results
in deformation of steel of wheel and the rail creating an elliptical contact area. The
dimensions of contact ellipse are determined by the normal force on contact area,
while the ratio of ellipse axes a and b depends on the main curvature of the wheel
and rail profile. Inside the contact area a pressure distribution develops which in a
cross section, is shaped in the form of a semi-ellipse with highest contact pressure
occurring at centre
The concentrated load between wheel and rail causes a shear stress distribution in
railhead as shown in fig.
The contact problem is most serious in case of high wheel loads or relatively small
diameters. Eisenmann has devised a simplified formula to calculate the maximum
shear stress in rail head, which is as follow
Since problem is one of the fatigue strength, the permissible shear stress is restricted
to 30% of UTS, which works out to be 21.60Kg/mm2 for 72UTS rail and 27.00
Kg/mm2 for 90 UTS rails.
The important deviation from the above formula is that the maximum shear stress
increases with increase in axle load. It also increases with increase in curvature of
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track as increase super elevation results in increase on loading of inner rail when
goods train ply on mixed traffic routes. The shear stress also increases with wearing
of wheels as the wheel radius decreases with the wear of wheel. Thus it may appear
that the problem of increase axle load can be solved with increase in wheel diameter
but this is not possible as increase in wheel diameter means less carrying capacity
because of restricted overhead clearances. Therefore only way to keep the maximum
shear stresses within permissible limits is to use the rail with higher UTS.
The contact stresses for BOY, BOB and BOXNHA wagons would be as under. The
diameter of wheel of Casnub bogie is taken as average of new wheel and worn out
i.e. (1000+925)/2=962.5 mm.
For 72 UTS rail the maximum allowable shear stress will work out to 21.60 Kg/mm2
and for 90 UTS rail, it will be 27Kg/mm2. It there implies that 90 UTS rail will be
required for running 30 tonne axle load.
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and sleeper is computed based on based on the principle of discretely supported rail
on springs at specified intervals. Using this principle and Dynamic Amplification
Factor because of the dynamic interaction between rail and wheel due to the speed
of train, the maximum bearing force on a single discrete rail support due to the
wheel load is obtained from the formula
• Based on Beam on Elastic Foundation M odel
Bearing Force on Sleeper –
Based on the charts developed by RDSO in their report no C-100 for different
Rolling stock based on experimentation, the speed factor for BOX wagons for a
speed of 100 Kmph comes to 1.68, However , since the wagon of 30 t Axle load
would be different with different dynamic characteristics , the dynamic effect due
to speed is also checked based on the formula proposed by Elisenmann for Dynamic
Amplification factor
• As per Eisenmann’s Formula,
• DAF = 1 + t ø {1+(V- 60)/140}
t = M ultiplication Factor Depending on Confidence Interval and
Ø = Factor Depending on Track Quality.
• For confidence t = 3, Ø =0.2 for average track quality and 100 kmph speed,
DAF works out = 1 + 3 x 0.2 {1 + (100-60)/140} = 1.78
• For 75 KM PH, DAF works out to 1.66
• Speed factor of 1.68 is adopted for computation of stresses
• In the absence of relevant data regarding the type of rolling stock and the speed
that would be permitted for the purpose of computation of stresses on sleepers
ballast and formation a speed factor of 1.68 is adopted based on the above
computed values and RDSO.
For 30 t axle loads, the effective wheel load ‘P’ would be 15t.
• The M ean Contact Pressure Between Rail and Sleeper on the most heavily
loaded sleeper would than be computed from the formula: -
óm. = (Fo + Fmax) / A
Where
• Fo = The total pre-tensioning force of fastenings on rail support (T)
A = Effective rail support area (mm2)
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“ A “ would be 0.125 X the width of the rail foot, since the width of the grooved
rubber pad used below the rail is 125mm.
For calculation purpose, it is normal to presuppose that the contact force is
distributed evenly over the contact surface area.
• The Contact pressure between rail and sleeper for 52 Kg and 60 Kg rail sections
for 52 kg or 69 kg P SC sleeper and also for sleeper spacing of 60 cm and 65 cm
computed basis on the above formulae are:
Permissible contact pressure between the rail and sleeper for concrete sleepers is
4N/mm2.
But as seen from computations in the above table, contact pressure value at the rail
seat for a track with 52 kg rail either on 52 kg or 60 kg sleepers would be far
excess of permissible value when 30 t axle load rolling stock is introduced.
Contact pressure are higher than the permissible value even for a track with 60 kg
rail on 60 kg sleepers at 60 cm spacing. As computed above a track with 60 kg
rail on 60 kg sleepers at 43 cm spacing only fit for running of 30 Ton axle load
rolling stock from contact pressure criterion on PSC sleeper. This poses a very
severe restriction, which would have far reaching implications and hence needs to
be examined thoroughly before introduction of 30 t axle loads.
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which the sleeper is made plays no role. The maximum stress between the sleeper
and the ballast bed under the wheel load ‘P’ is expressed based on Zimmermann’s
theory and by applying a Dynamic Amplification Factor due the speed of the
Rolling stock as per Eisenmann’s model.
= Fmax/Asb
Where Asb = Contact area between sleeper and ballast bed for half sleeper (mm2)
The permissible contact pressure on the ballast bed is taken as 0.50 N/mm2. As seen
from the values in the above table, for the present track structure, stresses on the
ballast bed would be whining the permissible value when 30 tonne axle load rolling
stock is introduced.
It can be gathered from the above equation that sleeper spacing and the
extent of ballast support area have an important influence on the mean stress on
ballast bed. A high value for foundation leads to high value of stress on ballast bed,
whereas heavier rail profile has a positive effect in this respect. A heavier rail profile
has a greater influence on rail stress reduction. The effect of ballast stress however,
is approximately half of the effect on the rail stress.
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on individual sleeper due to axle load, compressive stresses on the formation are
calculated from the following formula.:
The modulus of elasticity and permissible stresses on the formation for 2 million
cycles of loading as indicated by Coenraad Esveld are reproduced below:
Obviously, with introduction of 30 tonne axle load rolling stock, in most cases,
formation stresses would exceed the bearing capacity of the formation.
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3.0 IMPLICATIONS AND SOLUTIONS
FOR RUNNING OF 30 T AXLE LOAD ON
EXISTING TRACK
3.1 IMPLICATIONS ON RAILS:
3.1.1. Increased Contact Stress & Early fatigue Failure
If the permissible stresses are exceeded there will be plastic flow of metal at contact
and development of cracks in railhead will take place. These cracks grow gradually
due to combined effect of contact stresses with the entrapment of water or lubricant
resulting is surface breaking. If allowed to grow, they have potential go subsurface
and cause a failure by combining with already present defect. Another implication is
that if the surface cracking is severe, the substantial amount ultrasonic waves
transmitted will be reflected from these surface defects making it impossible for the
rail section to be reliably inspected for full depth.
The most prominent defects with the heavy haul are Rolling Contact Fatigue defects
predominantly the Gauge Corner Fatigue.
The maximum shear stress is developed not on the contact surface but at a depth of
5-7mm below the railhead. It therefore implies that use of head hardened rails will
be effective only if such hardening increases the UTS up to the depth of 6 mm or
more from the railhead. It is interesting to know the effect of surface hardening and
lubrication in context of maximum shear stresses. If wear is not dictating the life of
rail, as on head hardened rail / lubricated rails, the maximum repetitive shear stress
will always occur at same point, thereby increasing propensity of fatigue failure and
shelling.
On the other hand if the rail is allowed to wear, the point of occurrence of maximum
shear stresses will gradually shift downwards making it less prone to shear fatigue
failures or shelling. Therefore, it is paradoxical to say whether the use of head
hardened rails / lubrication of rails will actually enhance or reduce the life of rails
with heavy haul. Tests at Facility for Accelerated service Testing (FAST) have also
shown that higher wear rates of rail not only reduce surface defects but also suppress
the internal defects i.e. detail fractures and shelling.
From the analysis of bending stresses and contact stresses it may though appear that
52 Kg 90 UTS rail may suffice the requirements of increased axle load, but in
practice, the above stresses coupled with thermal stresses and residual stresses set up
cyclic stresses. From the theory of fatigue, it is evident that such cyclic stresses may
result in failure of material at a stress level lower than what would normally require
for failure.
Allan M Zarembski compared the rail life based on wear limits to rail fatigue life for
different axle loading environment and found that in lighter axle loading
environments, rail wear is dominant mode of failure while in heavier axle load
environments, the fatigue emerges as dominant replacement criterion.
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Rail Fatigue Life vs Wear 136 RE Rail
AREA Bulletin No. 685, Vol 83 reports of study made by Dr. Allan.M .Zarembski
on the effects of increasing axle loads on tangent track on a continuous welded track.
Two independent studies were conducted to determine the fatigue life of rails with
different axle loads. The first study involved the study of rail defect data to obtain
the probability distribution curves. Analyses of rail defects have shown that the
probability of their occurrence is a function of tonnage (M GT) and it follows
Weibull Distribution. The cumulative defect data was found to have linear
relationship with the accumulated M GT when plotted on Weibull’s scale. The defect
datas collected from two mining railroads operating with different axle loads and
compared with those of a mixed railroad. The results have shown that heavier axle
loads have resulted in a more severe occurrence of rail defects.
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The second study was the analysis of the rail life under fatigue. The effect of traffic
load, calculated rail head stresses (Bending, contact, thermal and residual stresses),
material properties of rail steel were analysed using the cumulative damage fatigue
theory which postulates that every increment of stress beyond the fatigue strength of
material causes fixed amount of damage. The fatigue lives of rails were then
calculated for different types of service environment.
The study had two conclusions:
1). An increase in axle loading will result in decrease in the fatigue life of rail,
measured in terms of cumulative M GT and reduction occurs for both heavier as well
as lighter sections.
ii). When the axle loads are increased from 27.5 tonnes to 33 tonnes (corresponding
to 70 tonnes and 100 tonnes freight cars), the resulting decrease in life of rail was
found to be 40 %.
Thus under Indian Railways context, it can be said that with increase in axle load
upto 25 tonnes, 52 Kg/m, 90 UTS rail may even though be permitted from the
considerations of bending stresses and contact stresses, however, in the interest of
long term economy and from fatigue considerations, it will be more appropriate to
use a heavier section of 60 Kg/m if further increases in A xle loads are imminent.
SOLUTIONS
3.1.2 RAIL GRINDING
A better solution to increase the life of the rails on Heavy Haul Routes is rail
grinding. Such grinding will remove the plastic deformation on railhead thereby
removing the surface cracks before they propagate further into rail section. It also
helps in progressively lowering the point of maximum shear stresses thereby
increasing the life of the rail and prevention of sub surface cracks due to fatigue.
Rail grinding is done primarily to
1. Shift the wheel loads from the gauge corner of running rail surface by
asymmetrical grinding pattern.
2. Prevent area of high- localised stress by grinding the corrugated profile to
confirm to wheel geometry.
3. Grinding at predetermined intervals shifts the critical internal stresses,
thereby not allowing micro cracking and subsurface failure to occur.
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Rail grinding removes the plastic deformation on rail head- helps in progressively
lowering the point of maximum shear stress thereby increasing the fatigue life of
rail
Prevent areas of high localized contact stresses by grinding the corrugated profiles
more conforming to wheel geometry, thereby distributing internal stresses more
uniformly, into the rail cross section
Grinding of rails using LORAM SX-11 rail grinder has been done on Kottavasla –
Kiramdul line, which has shown reduction in rail wheel contact stresses and
consequent failures.
On curved track with heavy haul traffic - pronounced side wear on outer rail,
gauge face corner defects
Flattering of rail head due to plastic flow of material on inner rail
The grinding not only makes the operation of heavy haul safer but also brings about
a long-term economy. It has been demonstrated on Sweden’s iron ore line, the
M alabanan, that by preventive grinding over a period of 3 years, the Rolling Contact
Fatigue defects were considerably reduced. The M almbanan is claimed to be
Western Europe’s only heavy haul line insofar as it carries fairly long trains with
relatively high axle loads of 25 tonnes and relatively high annual tonnage of about
23 GM T. The line suffered from the problem of RCF defects like stalling, shelling
and head checking. These defects were primarily observed on the high rail of curves
and in switches and were a cause of considerable concern. A preventive grinding
strategy was adopted where the rate of metal removal was about 0.20 mm across the
railhead after every 23 GM T. By adopting this preventive grinding, the cost of rail
grinding and rail decreased by more than 30 %. The principal savings came from
the purchase of rails, which declined, by two thirds over the period 1997-99, from
over 6 million crowns to about 2 million crowns, while the cost of grinding
remained constant at about 5 million crowns. Thus the Railway was not only less
expensive but also safer.
Thus it can be concluded that the Grinding will be effective strategy both in terms of
safety and long term economy, for the heavy haul routes as it helps in prolonging the
life of costliest component of track, the rail.
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3.1.3 Effect on curvature and track geometry
ORE 161 studies reports that Dynamic effects of 22.5 tonnes axle loads for
different speeds, track quality and radius of curvatures
Poorly maintained track will have most pronounced effect, where increase in the
wheel force can be up to 22 % of axle loads for speed ranging between 60 to 100
Kmph observed
Track quality was expressed in terms of standard deviation of vertical profile and
alignment
σ <1mm very good, 1-2 mm good > 2mm moderate
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SOLUTIONS
Head hardened rails should be used. Extra ballast profile should be given at curves.
Lubrication of gauge faces should be done at closed intervals.
On Indian Railways, the permitted sizes of wheel flats are 50mm for locomotives
and coaching stock and 60mm for goods stock.
The largest loads applied to the track from vehicles are those, which arise from
irregularities on wheel such as wheel flat. ORE 161.1/RP 3 reports of the tests
carried out on flat tyres measuring the effects of speed, size, sleeper type and axle
loads. The results reveal:
I) The forces at frequencies above 500 Hz referred to as P1 forces increases
continuously with speed, while the forces at frequencies below 100 Hz, referred to
P2 forces are more of less independent of speeds. The P1 forces have bearing on
wheel rail contact stresses. This force, which causes most of damage to rails and
concrete ties, increases with increase in speeds.
ii). Increase of axle load from 20 t to 22.5 t (12.5%) caused the increased wheel flat
force of the order of 0 to 6 %. Hence if go from 22.5t to 30 t the increase in wheel
flat force will be of the order of 24%.
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Studies have also revealed that movement of wheels with flats can generate
dynamic forces, as high as six times the normal static load, in extreme situations.
On Indian Railways, the effect of rail/ wheel defects and vehicle suspension, on
static wheel load, is represented by a speed factor (Rail stress calculations), which
can assume a maximum value of 1.75 for locomotives and 1.65 for wagons.
The problem assumes alarming proportions incase of thermit welds (which have
the impact strength of 7-10% of parent rail) in LWR territories, during winter
season, when the full tensile stresses are present in rail section.
Spate of weld failures due to running of flat tyres under these conditions, is not
uncommon.
Studies have also revealed that movement of wheels with flats can generate dynamic
forces, as high as six times the normal static load, in extreme situations. The
Dynamic forces increase with increase in speed and axle loads. On Indian Railways,
the effect of rail/ wheel defects and vehicle suspension, on static wheel load, is
represented by a speed factor, which can assume a maximum value of 1.75 for
locomotives and 1.65 for wagons. However the studies conducted by ORE shows
that the dynamic loads can increase up to 6 times static wheel load and further by
6% due increase in axle loads. Such occasional high loads may result in higher rail
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stresses reducing the fatigue life of rails and causing fracture of rail/ welds in
extreme cases. The problem assumes alarming proportions in case of thermit welds
(which have the impact strength of 7-10% of parent rail) in LWR territories, during
winter season, when the full tensile stresses are present in rail section. Spate of weld
failures due to running of flat tyres under these conditions, is not uncommon.
SOLUTIONS
Codal provisions of tolerances of flat wheel require to be changed. M onitoring of
flat wheels should be done closely and en route detachment of wagons with flat
wheels should be done.
The US studies revealed that the defect size more than 15% have direct implication
due to wheel flat and failure rate is more. The USFD should be carried out within
the periodicity of 8GM T so that defects of sizes more than 15% shall be detected in
time.
As illustrated in the formula for computation of bearing force on rail support, sleeper
spacing proves to a relatively great influence on support force. Similarly, Use of
heavier rails would reduce bearing force, where as increased support stiffness of
track would result in increased bearing pressure on discrete sleepers. In the most
unfavorable case, bearing pressure may be of the same order of magnitude as the
effective wheel load ‘P’.
SOLUTIONS
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3.3 IMPLICATIONS ON BALLAST AND
FORMATION
The permissible contact pressure on the ballast bed is taken as 0.50 N/mm2. As seen
from the values in the above table, for the present track structure, stresses on the
ballast bed would be whining the permissible value when 30 tonne axle load rolling
stock is introduced.
Obviously, with introduction of 30 tonne axle load rolling stock, in most cases,
formation stresses would exceed the bearing capacity of the formation. Blanketing is
to be done for whish extra cost of 10 Lac/Km will be involved.
SOLUTIONS
This would necessitate provision of a blanket layer of adequate thickness to
improve the bearing capacity just beneath the ballast bed. Provision of blanketing, in
accordance with the recent guidelines issued by RDS O in June 2003 vide
Guideline No. GE: G-1, appears to be the only solution for stabilising weak
formations. It is obvious that a yielding formation will result in rapid deterioration of
track geometry, which will make it unsafe of higher axle load trains in addition
necessitating increased and frequent maintenance efforts.
o Provision of a blanket layer on running tracks under traffic, however is going
to be a difficult task due to the obvious constraints such as availability of
Engg. Time Allowance; line Blocks, restricted working space, safety
implications, difficulty in completion etc.
J P Hyslip & E T Seli, S S Smith and G R Oleoft, have reported of Ground
Penetrating Radar (GPR) being employed to assess conditions in railway track
substructure (ballast, sub ballast, and sub grade) and to produce quantitative indices
of substructure condition for use in track maintenance management efforts. GPR
surveys have been conducted on over a combined 100 miles of track, including
mainline and freight tracks. Results of these surveys have shown the ability of GPR
to distinguish between the different substructure layer conditions to determine areas
of trapped water and fouled ballast.
The railway GPR equipment is mounted on a hi-rail vehicle and includes
multiple sets of 1-GHz air launched horn antennas suspended above the track that
permit fast survey travel speeds and high resolution measurements to a depth of 4 to
6 ft (1 to 2m). The antenna configuration and surveying procedures are deployed to
reduce the influence of sleepers and rail. Antennae are located at both ends of the
sleepers as well as in the centre of the track, so the variations of conditions laterally
across the track are seen.
The GPR method requires transmitting pulses of radio energy into the subsurface and
receiving the returning pulses that have reflected off interfaces between materials with
different electromagnetic properties. Antennae are moved across an area with a
continuous series of radar pulses, giving a profile of the subsurface. Reflections of the
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GPR pulse occur at boundaries in the subsurface where there is a change in the material
properties. Only a portion of the pulsed signal is reflected and the remaining part of the
pulse travels across the interface to again be reflected back to the receiver from another
interface boundary. The time the pulse takes to travel through the layer and back is
controlled by the thickness and properties of the material. The travel time between upper
and lower boundaries of a layer can be used to calculate the layer thickness employing a
known velocity.
While running 30 t axle loads, impact stresses on the ballast will increase and this
further lead to crushing of ballast. Therefore, deep screening of ballast is required at
close interval of time.
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3.5.3 Findings of The AAR Panel on 100-Ton Cars
In 1981, an AAR panel of distinguished railroad engineers compared the expected
impacts on 80 tonne loading cars (20 t axle loads) on well maintained tangent track
with 60Kg rail continuous welded rail to the expected impacts of 263,000- pound
cars 9100 ton loading cars) on the same track. The panel concluded that rail life
would be 1.5 to 2.1 tonnes greater using the 80 ton cars, while tie and ballast life
would be1.0 to 1.4 times greater under traffic loads. The panel report also noted that
the impact of heavier 100-ton cars would be much greater on light rail and poorly
maintained track. However these reports were not quantified.
Findings of the Ahlf Study of 100-Ton Cars.
SOLUTIONS
Strict tolerances for the track parameters should be be kept. M aintenance inputs are
required to be increased. Use of superior materials to increase the life cycle should
be used. M echanised maintenance should be adopted. Deep screening and temping
should be done at closer interval than existing provisions.
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3.7 IMPLICATIONS ON SCHEDULE OF
INSPECTION
With the increase in axle load to 30 t the schedule of inspections of officials and
supervisors needs to have re look. Definitely frequency inspections will be
increased.
The strategy for running heavy axle loads of 30 tonne should comprise of following
alternative solutions;
It can be seen from the above that even in 60 kg Rail stresses are higher than the
permissible limit, in other words 60 kg 90 UTS Rail also not fit for 30 t axle loads.
23
The contact stresses for BOY, BOB and BOXNHA wagons would be as under. The
diameter of wheel of Casnub bogie is taken as average of new wheel and worn out
i.e. (1000+925)/2=962.5 mm.
For 72 UTS rail the maximum allowable shear stress will work out to 21.60
Kg/mm2 and for 90 UTS rail, it will be 27K g/mm2. It therefore implies that 90 UTS
rail will be required for running 30 tonne axle load.
The world’s longest rails are now manufactured in India for a length of 120m.
With the availability of 120 m long rails, there will be drastic reduction of weld
population in Indian rail tracks (from 160 welds per track km presently to 17)
resulting enhance safety and cost reduction.
24
Obviously, with introduction of 30 tonne axle load rolling stock, in most cases,
formation stresses would exceed the bearing capacity of the formation. This would
necessitate provision of a blanket layer of adequate thickness to improve the bearing
capacity just beneath the ballast bed. Provision of blanketing, in accordance with the
recent guidelines issued by RDSO in June 2003 vide Guideline No. GE: G-1,
appears to be the only solution for stabilising weak formations. It is obvious that a
yielding formation will result in rapid deterioration of track geometry, which will
make it unsafe of higher axle load trains in addition necessitating increased and
frequent maintenance efforts.
We have opted for Broad Gauge (5 feet 6 inches between rails against the standard
gauge world wide of 4 feet 8.5 inches) yet our moving dimensions are highly
restrictive. Similarly, productivity of our wagons in terms of tare to pay load ratio is
probably one of the poorest in the world. We carry 450 kg of dead weight for
moving every tonne of traffic as against 170 kg in developed countries. The wagons
should be redesigned to increase the cubic content and the load carrying capacity to
fall in line with the international norms.
No tippling for unloading should be resorted to.
Wagons should be equipped with end of train telemetry.
Coupling height should be 851 mm instead of 1105 mm at present. Lowering of
wheel diameter and coupling height substantially increases the volume available for
the payload
Bogie M ounted Electronic Brake System should be adopted.
Conforming to Liberalized M oving Dimensions
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5.2 COMMUNICATION INPUTS
The communication system should be 880 Hz. GSM R permitting direct
communication between Driver and Guard and the Section Control.
At present Indian railway has taken up the project of running 30 tonne axle load
between Deitari to Banaspani for a distance of 150 Km, which is a dedicated iron
ore route in East Coast Railway. The track structure adopted in this project is 60 Kg
90 UTS rails on PSC-60 Kg sleepers of 1660 Nos/Km with a clean ballast cushion
of 300 mm. At curves greater than 3 deg. 60 kg head hardened rails are used.
However, the speed of the goods train is proposed as 75 KMPH. All the Bridges and
formations are designed for High M ineral Loading Standards.
7.0 CONCLUSIONS
1. To carry more freight, cost effectively the Indian Railway must raise axle
loads to 30 tonne.
2. From the consideration of bending stresses and contact shear stresses, even
60 kg, 90 UTS rail is not able to sustain the increased stresses due to 30
tonne axle loads. 68.5 K g AAR or 71 Kg UIC rails seems to be a realistic
solution.
3. Contact pressure between rail and sleeper would be higher than the
permissible value even on a track with 60 K g rail on 60 K g sleepers (PSC-6)
at 60 cm spacing (1660 sleepers/Km).
300 mm clean ballast cushion would be required for running 30 tonne axle
load and the deep screening and temping needs to be done at closer
intervals.
26
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7. With the introduction of 30 Tonne axle load, in most of the cases, formation
stresses would exceed the bearing capacity of the formation. This would
necessitate provision of a blanket layer of adequate thickness as per RDSO’s
specifications for which extra cost of Rs. 10 Lac/Km will be involved. For
running 30t axle load in the existing track this will be most challenging job
due to field difficulty in carrying out the work.
9. The cost of the maintenance of the track with increase in axle loads from
20.32 t to 30 t is expected to increase by 3 times depending on the formation
and track quality as per AASHO test. This is still ambiguous since Swiss
model studies shows 3% increase in maintenance cost after doing rail
grinding and lubrication.
11. For running the 30t axle load in existing track increase frequency of
inspections , patrolling and U SFD testing are required. USPD should be done
in the periodicity of 8 GMT.
12. As an alternative strategy, use of wagons with high payload to tare ratio and
increased number of axles may also be considered. Wagon dimensions must
be changed with reduced wheel diameter. Signalling system requires to be
upgraded.
27
8.0 REFERENCES:
15. Technical Report No.4, on load carrying capacity of masonry arch bridges,
By Sh. R.R. Jaruhar, M ember Engg. Rly Board.
28
INDEX
PAGE
S.No. DESCRIPTION No.
1.00 Introduction 1
1.1 General 1
1.2 Wake up Call 1
2-3
Indian Railway has to embark upon a path of modernisation and
1.4 expansion in a big way, as per vision of PM .
3-4
1.4.1 Enhance Transport Capacity 4
3.0 Implications and solutions for running 30t axle load on existing 12
Track.
3.1 Implication on Rail 12
29
3.1.4 Effect of flat wheel 17-19
4.0 Implications and solutions for running 30t axle load on new Track. 23
8.0 References 28
30
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