Axle load for Rail way - linkedin

The axle load of a wheeled Rail is the

total weight felt by the railway for all

wheels connected to a given axle.

Viewed another way, it is the fraction of

total Train weight resting on a given

axle.

Axle load is an important design

consideration in the engineering of

railways and roadways, as both are

designed to tolerate a maximum weight-

per-axle (axle load); exceeding the

maximum rated axle load will cause

damage to the roadway or rail tracks.

The vehicle axle load is usually measured for the

Static condition, but in the design of railway track the actual

stresses in the various components of the track structure and in

the rolling stock must be determined from the dynamic vertical

condition and lateral forces imposed by the design Train moving

at speed.

The dynamic wheel loads cause increases in the rail stress values

above those of the static condition due to the following factors:

1. lateral bending of the rail .

2. eccentric vertical loading .

3. transfer of the wheel loads due to the rolling action of

the train .

4. vertical impact of wheel on rail due to speed .

The maximum axle load is related to the strength of the track .

strength of the track is determined by :

1. Weight of Rails .

2. density of sleepers .

3. track stability .

4. amount of ballast .

5. strength of bridges .

Loads are transferred

from the Wagon body into

truck and track structure

via the:

– center-bowl (1)

– bolster (1)

– spring-groups (2)

– side frames (2)

– bearing adaptors (4)

– bearings (4)

– axle journals (4)

– wheels (4)

– rails (2)

– sleepers (many)

– ballast

Principal components from top

down

• Rail

• Fasteners

• sleepers

• Ballast

• Sub-ballast

• Subgrade

Loads are distributed

downward through these

components

Rail is the single most valuable asset

owned by the railroad industry.

It is probably the most critical element

of track system.

Provides smooth, low-friction, running

surface, Wide, flat base distributes load

across several crossties and allows

fasteners and other stabilizing

components to be attached

Combined with fasteners and ties,

provides a stable track gauge .

The sleepers supports the rail and distributes

the load over a larger section of the sleepers

surface.

Fasteners hold the track in gauge and do not

provide much vertical restraint.

Along with fasteners, sleepers provide

gauge restraint and further distribute the

load into the ballast.

Ballast and sub-ballast are the final stages in load distribution

In addition to distributing vertical loads, ballast has a critical role

maintaining longitudinal and lateral stability of track.

Flange on the inside is

stable, rather then

unstable, when there is

a lateral force such as

in curves.

As a load is applied, it

results in both

downward and upward

forces on the rail and

consequently the track

structure.

This “pumping” action

as wheels pass over it

tends to loosen, wear

and damage track

components

lateral force :

the force of the wheel flange pushing

out on the rail.

vertical force :

the wheel load of the equipment

bearing down on the rail

In order for a wheel's flange to climb up the gage face of a rail and over the rail head to the outside of the track, the wheel lateral and vertical forces must be such that the vertical force that acts to keep the wheel on the rail is overcome by the lateral force and the friction forces that exist between the wheel's flange and the gage face of the rail.

L/V quantifies the ratio between the force of the wheel flange pushing out on the rail (lateral force) and the wheel load of the equipment bearing down on the rail (vertical force). The single wheel L/V ratio can be used to predict the risk of a wheel climbing the gauge face of the rail or lifting off the rail. Similarly, the combined forces for the wheels on one truck side exerting high lateral forces onto the same rail can cause rail-head deflection, reverse-rail cant, or lateral-rail displacement, resulting in gauge spread or rollover.

AAR guidelines indicate that truck side L/V values should not exceed 0.6

The Nadal formula, also called Nadal's

formula, is an equation in railway design

that relates the downward force exerted by

a train’s wheels upon the rail, with the

lateral force of the wheel's flange against

the face of the rail. This relationship is

significant in railway design, as a wheel-

climb derailment may occur if the lateral

and vertical forces are not properly

considered

L and V : refer to the lateral and vertical forces acting upon the rail and wheel

δ : is the angle made when the wheel flange is in contact with the rail face

μ : is the coefficient of friction between the wheel and the rail .

Typically, the axel load for a railway vehicle should be such that the lateral forces of the wheel against the rail should not exceed 50% of the vertical down-force of the vehicle on the rail. Put another way, there should be twice as much downward force holding the wheel to the rail, as there is lateral force which will tend to cause the wheel to climb in turns .

This ratio is accomplished by matching

the wheel-axle assembly of railroad

car (wheelset) with the appropriate rail

profile to achieve the L/V ratio desired.

If the L/V ratio gets too high, the wheel

flange will be pressing against the rail

face, and during a turn this will cause

the wheel to climb the face of the rail,

potentially derailing the railcar .

The Nadal formula assumes the wheel

remains perpendicular to the rail—it

does not take into account hunting

oscillation of the wheel-axle assembly

of rail car (wheelset), or the movement

of the wheel flange contact point against

the rail.

A variation of the Nadal formula, which does take these factors into consideration, is the Wagner formula. As the wheelset relative to the rail, the vertical force V is no longer completely vertical, but is now acting at an angle to the vertical, β. When this angle is factored into the Nadalformula, the result is the Wagner formula

When the vertical force is truly vertical (that is, β=0 and

therefore cos(β)=1), the Wagner formula equals the Nadal

formula .