W1 tracks kirse jb

1Light Rail Transit Facilities Design Course

Track Design


Track Design

Light Rail Transit Facilities

Design Course

Track Design05.12.2010

2

By: Ken KirseCivil Engineer, TriMet


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


Track Design

Wheel – Rail Interface

• Wheels• Where does flange go


Track Design


Track Design

Why are flanges on the inside of wheels?


Track Design

Rail Sections

“Tee” Rails

Girder Rails


Track Design


Track Design

Curving Characteristics

With solid axlesWith stub axles


Track Design


Track Design

Track Design

• Gage• Tie and ballast open track• Basis of design of tie and ballast track• Embedded on paved track


Track Design


Track Design

Modulus of Track Elasticity ()

Defined as the load per unit length of rail required to depress that 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


Track Design

Maximum Deflection Y0 of Rail

Y0 =p

(64 3) ¼

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”


Track Design

Maximum Rail Bending Moment (M0)

M0 = p

64

¼


Track Design

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


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.


Track Design

Unit Pressure (Pa) Transmitted from Bottom of Tie to Ballast (psi)

Pa = 2P

2/3 bL

3P

bL=

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


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 =

S

30,000,000

Rail Stress from Temperature Change


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 Joints tested to 600,000 lbs

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

= 195 psi

Rail Stress from Temperature Change


Track Design


Track Design

Embedded Track

• Aesthetics• Maintenance considerations• Concrete track slabs• Covered tie and ballast track


Track Design


Track Design

Common on bridgesDF fastenersMethods of construction

Direct Fixation Track


Track Design


Track Design

Material for Light Rail Track

• Ties• Bumping posts• Switch heater• Switch stands• Insulated joints• Automatic train stop


Track Design


Track Design

Light Rail Track Road Crossings

• Design considerations• Crossing materials• Drainage


Track Design


Track Design

Light Rail Track Drainage

• Open track under drains• Paved track drainage• Special Trackwork Drainage


Track Design


Track Design

Special Trackwork

• Definition of turnout components

• Turnout size, frog number• Frog types• Girder rail turnouts• Rail crossings, restraining rail


Track Design


Track Design

Noise and Vibration

Problem Areas• Tri-Met history with Westside

Project• Noise and vibration mitigation


Track Design

P49


Track Design


Track Design

P51


Track Design

P52


Track Design


Track Design

Electrical Isolation

Causes of stray current• Why is stray current a problem?• Methods of controlling stray current• Monitoring stray current


Track Design

W1 tracks kirse jb

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