Rail Track

7/30/2019 Rail Track

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1Light Rail Transit Facil itiesDesign Course

Track Design


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Track Design

Light Rail Transit FacilitiesDesign Course

Track Design05.12.2010

2

By: Ken Kirse

Civil Engineer, TriMet


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Track Design

Light Rail Track Design

Wheel-Rail Interface Track Design

Light Rail Track Materials

Track Road Crossings

Drainage Special Trackwork

Noise and Vibration

Electrical Isolation


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Track Design

Wheel Rail Interface

Wheels Where does flange go


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Track Design


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Track Design

Why are flanges on the inside of wheels?


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Track Design

Rail Sections

Tee Rails

Girder Rails


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Curving Characteristics

With solid axlesWith stub axles


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Track Design

Gage Tie and ballast open track

Basis of design of tie and ballast track

Embedded on paved track


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Modulus of Track Elasticity ()

Defined as the load per unit length of rail required to depressthat rail by one unit.

p = - y

p = upward pressure per unit length = track modulus of elasticity (track stiffness)

y = vertical deflection of rail

with wood ties = 2000 Avg., 1000 poor, 5000 stiff


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Track Design

Maximum Deflection Y0of Rail

Y0 = p(64 3) Y0= maximum deflection (x=0, under wheel)

p = Dynamic wheel load (static load + 1% per MPH over 5 MPH)

= Modulus of elasticity of rail steel (30 x 106 psi)

= Moment of Inertia of rail (65.6 in4 for 115RE)

= Track modulus of elasticity

AREMA recommended limit of deflection is 0.25


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Track Design

Maximum Rail Bending Moment (M0)

M0 = p64


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Maximum Rail Bending Stress

M0C

S =C = distance in inches from the base of rail to its neutral axis

AREMA recommended maximum = 25,000 psi

Rail steel yield point = 70,000 psi


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Track Design

Ballast Pressure Under Centerline of Tie(PC)

PC =16.8 Pa

h 1.25

Pa = uniformly distributed pressure over the tie face

h = depth below bottom of tie in inches

Pc of 20 psi is AREMA suggested value for firm subgrade soil.


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Track Design

Unit Pressure (Pa) Transmitted from Bottom of Tie toBallast (psi)

Pa = 2P2/3 bL

3PbL

=

P = wheel load (lbs) 2P = Total tie load

L = Tie length in inches

b = Tie width in inches

2/3 = factor for 2 load bearing thirds of tie

Pa should not exceed 65 psi for wood ties

85 psi for concrete ties


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Track Design

115RE rail

Area = 11.2465 sq.in.

Moment of Inertia about neutral axis = 65.9

Yield Strength 70,000 psi min.

Modulus of elasticity E 30x106 psi

To determine tensile force for temperature change.

Rail changes 0.0000065 of its length per degree. F

S = unit stress .0000065 t = S30,000,000

Rail Stress from Temperature Change


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Track Design

For 70F change

Total Restraining Force F = 70x195 x 11.2465

F = 153,515 lbs

Yield Point of 115#Rail

70,000 x 1102465 = 787,255 lbs

Insulated J oints tested to 600,000 lbs

For 1F change S = 30,000,000 x 0.0000065x1= 195 psi

Rail Stress from Temperature Change


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Embedded Track

Aesthetics Maintenance considerations

Concrete track slabs

Covered tie and ballast track


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Track Design

Common on bridgesDF fasteners

Methods of construction

Direct Fixation Track


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Material for Light Rail Track

Ties Bumping posts

Switch heater

Switch stands

Insulated joints Automatic train stop


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Light Rail Track Road Crossings

Design considerations

Crossing materials

Drainage


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Li ht R il T it F il iti


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Light Rail Track Drainage

Open track under drains

Paved track drainage

Special Trackwork Drainage



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Light Rail Transit Facil ities


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Special Trackwork

Definition of turnout components

Turnout size, frog number

Frog types

Girder rail turnouts

Rail crossings, restraining rail



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Noise and Vibration

Problem Areas

Tri-Met history with Westside Project

Noise and vibration mitigation



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Electrical Isolation

Causes of stray current

Why is stray current a problem?

Methods of controlling stray current

Monitoring stray current


Track Design


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Documents

Rail Track