CEE 412 Flashcards
What is railway track engineering?
Engineering discipline engaged in planning, design, construction, inspection, Maintenance, Advancement of track structure
Evolution of track structure
Has evolved over past 200 years Changes often to increase train loads and speed Trial and error approach Analytical approach began end 1800s Modern: mechanistic design
Primary function of track
Support and distribute train loads Guide the vehicle Provide adhesion at wheel-rail interface Provide smooth running surface Facilitate drainage
Secondary function of track
Transmission of signal circuit
Broken rail detection
Path of ground return for traction power
Track engineering fundamental
Providing adequate drainage
Where does the water go
Track components
Welded rail Crosstie Fastener Tie plates Spikes Rail anchors
Rail pads
Where is track gauge measured
distance between heads
5/8“ (15.875mm) below the top of the rail
Track gauge examples
Spain, India 1767 Russia 1524 UIC 1435 South Africa, japan 1067 Switzerland, india 1000 Russia 750
Klingel Motion
Amplitude/Cycle length
Lk=2Pi sqrt(rs/2gamma)
y=y0sin(2pix/L)
Truck hunting
Lateral, side to side steering motion
Influenced by speed, carbody resonance, wheel conicity, rail head geometry, suspension
Can lead to excessive rail wear, wheel wear, wider gauge, derailment
Quasi static Forces acting on the track
Groß tare
Centrifugal
Wind
Dynamic forces acting on the track
Track irregularities
Discontinuities
Irregular running surface
Vehicle defects
Vertical forces acting on track
Similar for lateral
P total =
P static +
P centering (curvature,cant) +
P wind +
P dynamic
Longitudinal Force on track
Thermal force
Traction force
Braking force
Calculating dynamic wheel load
Dynamic load> static load
Pd = Ps + thetaPs
Impact factor theta:
33V[MPH]/(D[inches]100)
Size of a contact patch
1/2 sq. In.
Track performance requirements
Stiffness Resilience Resistance to permanent deformation Stability Alignment and adjustability
Criteria for success
Safety
Cost:
Reliability, availability, maintainability
Comfort
Components of track superstructure
Rail
Ties (sleeper)
Fastening system
Components of track substructure
Top Ballast Bottom ballast Subballast Placed foil (fill) Natural ground
Importance of the wheel-rail Interface
Low friction for efficiency
Strength to resist vertical forces
Wear and fatigue resistance for cost effective operation
Key aspects of rail metallurgy
Chemical composition Cleanliness of steel Microstructure Hardness and wear resistance Tensile properties
Additional Chemicals in rail steel
Wanted or unwanted
C Mn Si S P Cr V
Definition: Hardness
The ability of a material to resist penetration, scratching, wear, abrasion and cutting
Definition: ductility
The ability of a material to undergo relatively large plastic deformations before fracture
Definition: toughness
The ability of a material containing a crack to resist fracture
Key rail dimension
Head shaped to meet wheel contour
Broad base to resist overturning
Base shaped to facilitate fastening to ties
Web connects head and base
Standard rail sections
136 RE. 136 lb/yd
UIC 60. 60 kg/m
Typical hardness of rails
Measured in brinnel hardness:
200-240
…
350-390
Continous welded rail
Welded to eliminate joints
Length > 400 feet
(200-800m)
Needs control of thermal stresses
Must be anchored
Crosstie fundamentals
Maintain gauge
Distribute wheel loads from rails to ballast
Anchor track against lateral, longitudinal, vertical movement
Spacing: 18-30“
Function of fasteners
Longitudinal resistance
Torsion resistance
Lateral, vertical flexibility
11 Functions of ballast
Transmit and reduce tie pressure to subgrade
Anchor rail-tie structure
Absorb dynamic impact
Facilitate drainage
Provide dry support medium to prolong service life of ties
Facilitate maintenance
Reduce occurrence of track frost heave
Prevent vegetation growth
Provide voids for „storage“ of fouling material
Absorb noise and vibrations
Provide electrical resistance between rails
Important ballast properties
Particle size, gradation, shape
Resistance to weathering, fragmentation, degradation
Compressive strength
Clean and cleanable
Workability for alignment adjustments
Ballast material suitable for HSR
Crushed stone
- granite
- quartzite
- basalt
- traprock
(Hard, durable, good repeated load behavior)
Sources of fouling
Ballast breakdown
- handling
- thermal stress
- freezing water
- tamping damage
- Traffic damage
Infiltration from ballast surface
Tie (sleeper) wear
Infiltration from underlying Granulat layers
Drainage requirements
Keep the ballast clean enough for water to drain as fast as it enters
Have the surface of the subballast and subgrade slopes away from the center of the Track
Provide a means for water coming out of the substructure to drain away from the track
Design principle of slab track systems
Enough strength and stability: high safety
Reasonable design scheme of manufacturing, laying and fine-adjusting of track structure: smooth
Reasonable structure types and durable engineering material: low maintenance
Classification of loads
Slab track
Dead load
- structure weight
- shrinkage
- creep of concrete
Live load
- vertical, lateral, temperature force
- flexure of support
Additional loads
- braking, traction force
- uneven settlement of support layers
Special loads
- temporary construction forces
Dynamic evaluation of slab track
Safety index
- derailment coefficient
- rate of wheel load reduction
Comfort index
- carbody acceleration
Dynamic response index
- vertical, lateral force
- acceleration
- vibration, noise
Typical uses for continous/discrete concrete bed structure
Cobtinous:
- subgrade
- tunnel sections
Discrete:
- bridges
Technical features of pre-cast slab track
High concrete structure quality
Environmental and weather influence reduced
Allows scheduling efficiencies
Advantages of ballasted tracks
Low initial construction cost
High elasticity
Simple maintenance at low cost
High noise absorption
Easier to renew on existing lines
Less complex drainage systems
Advanced maintenance techniques
Advantages of slab track
Higher level of track stability
More precise control of alignment
Improved ride comfort
Longer life cycle
Minimal maintenance requirement
Higher availability
Reduced structural height
Disadvantages of ballast track
Rate of geometry deterioration
Lower lateral track resistance
Fouled ballast inhibits drainage
Weight increases cost on bridges
Increased structural height
Ballast flight st high speed
Disadvantages of slab track
Higher initial construction cost
Complexity of construction
Sensitivity to construction defects
Less long-term experience
More susceptible to settlement
Less sound & vibration absorption
Decision between ballast/slab:
Operational concept
Availability for operations
Business case
Ride comfort requirements
Decision between ballast/slab:
Production & maintenance concept
Maintainability
Possibility of making adjustments
Replacement investment requirement
Availability of component supplies
Decision between ballast/slab:
Risks/ malfunctions
Safety
Pattern of damage & repair following derailment
Remediation of defects
Decision between ballast/slab:
Miscellaneous requirements
Drainage
Structure-borne noise
Airborne noise
Effects on the subsoil
Clearance gauge
What are the current types of slab track on the market?
Cast in site concrete
Precast concrete elements
