CE-363

Lecture 7: Creep in Rails

Dr. Ankit Gupta, Assistant Professor

Department of Civil Engineering

National Institute of Technology Hamirpur

Lecture Outline

Creep in Rails

Effect of Creep

Theories of creep

Creep Indicator

Methods to reduce Creep

Creep - Definition

Longitudinal movement of rails in a track

Location specific

Varies in magnitude

Creep - Indicators

Closing of joints in the direction of creep

Opening of joints at points where creep starts

Scrapping / scratching marks on rail flanges / web due to spike head

Creep - Effects

Opening or jamming of joints

Kink formation at rail joints

Sleepers get out of position affecting gauge and alignment

Buckling of track derail the train

Points, crossings, switches, interlocking gets distorted

Creep - Effects

Smashing of fish plates, bolts due to stresses induced

Removal, replacement, maintenance becomes difficult

Forging of ballast

Bending of bars

Creep - Theories

Wave theory

Percussion theory

Drag theory

Creep - Theories

Wave theory

Moving wheel loads set a wave motion in

rails.

A vertical reverse curve is formed ahead

of wheels in the rails

As wheel moves, the lift in front of the

moving load is carried forward, thus

causing creep.

Creep - Theories

Wave theory

Creep - Theories

Wave

theory

Creep - Theories

Wave theory

Wave action is controlled by PITCH and

DEPTH of wave

Pitch and Depth of wave depends upon

Track modulus

Track stiffness

Track stability

Creep - Theories

Wave theory

Control of Wave action

Use angular and heavy ballast

Lesser sleeper spacing

Bigger rail section

Increasing stiffness of track

Creep - Theories

Percussion theory

States that the creep is due to impact of

wheels at the rail end ahead at joints

At the rail joint, the wheel load presses

the trailing rail down thus causing an

impact of wheel with the forward rail

At strike, the force in the direction of

movement pushes the forward rail ahead

thus causing creep

Creep - Theories

Percussion theory

The resultant of vertical load and

forward force causes battering of rail

end (of forward rail).

Creep - Theories

Percussion theory

Creep - Theories

Percussion theory

Creep increases due to

Weak / loose fish bolts

Worn out Fish plates

Loose packing

Wide joint expansion gap

Heavy axle loads moving at fast speed

Creep - Theories

Drag theory

It relates to the motion of a locomotive

and the wagons

Driving wheels of the locomotive causes

backward thrust, pushing rail of the track

backward

Other wheels of the locomotive and

wheels of the wagons opposes this

motion (inertia effect) and push the rail in

the direction of travel

Creep - Theories

Drag theory

This is more than the effect of driving

wheels.

Creep - Other Causes

Starting,

Accelerating,

slowing, stopping of

wheels

- Starting or acceleration

causes backward thrust

- slowing or deceleration

causes push in rails in

forward direction

Thermal expansion /

contraction of rails

- Range in temperature

- effect of surroundings,

like shades

- location effect

Creep - Other Causes

Unbalanced traffic - heavy traffic in one direction

- Ill design of track

- More on curves

- More on steep

gradients

-

Poor maintenance of

Track

- type of rail (old / new;

light / heavy)

- fastenings, joints

- Ballast cushion,

formation

Creep - Measurement

Creep - Prevention

Pulling back the rails

Using crow bars and hooks through fish

bolt holes

Slow and tedious process

Practicable for only small lengths

Creep - Prevention

Use of steel sleepers

Steel through sleepers are best

Increase in number of sleepers can help

Rails Creep: Prevention

Using Anchors / Anti-creepers

4 anchors per rail if creep is 7.5 cm to 15

cm / month

6 anchors per rail if creep is 22.5 to 25 cm

/ month

used at level crossings, in yards and

places of heavy brake application

not used on bridges

Creep - Prevention

Creep - Prevention

Using Anchors / Anti-creepers

These are fastened to the foot of the rail

Anchors are fixed to rails either

By wedging action

By clamping

By a spring grip

Creep - Prevention

Important points

Should be able to resist the movement of the

rails

Should butt against the sleepers

Fixed to good sound sleepers

Should not be used on bridges