CE 515 Railroad Engineering
Railway Structures
Design Considerations
Source: AREMA Ch. 8
bad powerpoints video!
“Transportation exists to conquer space and time -”
Loading Design
• ACI , AISC , AASHTO
• AREMA Manual for Railway Engineers
• Different Types of Loadings
Differences From Roadway to Railroad
Structures
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Versus
Image from
http://images.google.com/imgres?imgurl=http://upload.wikime
dia.org/wikipedia/commons/
Life Span
• 100 Year Life Span
• Due to viable of alternative routes
Dead Loads
• Permanently remaining items supported by
the structure
• Track is 200lbs/linear ft.
• Ballast is 120lbs/ft3
• Treated Timber 60lbs/ft3
What went wrong
Image from : http://www.time.com/time/photogallery/0,29307,1649646_1421688,00.html
Live Loads
• Static and Dynamic effect load of vehicles
• Cooper E-Series loading Scheme (E-1)
Image from: http://www.tpub.com/content/armytransportation/TI-850-02/TI-850020112.htm
Cooper E-Series
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Conversions for modern to E-series
Bridge Specific Rating System
Bridges Rated off Limiting Structure
Service Rating vs. Ultimate Rating
Live Load 4-Axel
• Short Span Steel Members (<54ft)
• Heavy Intermodal Trains
• More Similar Loading to 4-axle coupled cars
Impact Loading
• Dynamic increment and impulsive loads
• Caused mostly by flat wheel spots
• Designer has no control over imposition
• Load amount derived from percent of live load
Flat Wheel on Engine
Steel Concrete and Timber Structures
Impact Loading
• Steel impact load is function of spacing of
supporting elements
• Differences for prestressed than cast-in-place
concrete impact loading calculations
• Not taken into account for timber due to
material properties and AWS design
Centrifugal Force
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Outward acting force on curve from train
Force bend structure laterally
Steel structure loads laterals and cross frames
Concrete Structures usually stiff enough to
resist
• Track super elevation offers some
compensation
Lateral Loads
• Nosing, hunting action, lurching and damaged
rolling stock
•
Train Hunting
• Due to routine train passage
Sssshhh. Be vewy
vewy quite. I’m
hunting twains.
http://www.flickr.com/photos/leadegroot/2311723124/
Longitudinal Loads
• Braking and Accelerating Force
• Distributed into the supporting structure
Wind and Stream/Ice/Buoyancy Loads
• Wind loading self explanatory wind force on
structure and train
• Stream loads are loaded in every way
horizontal, vertical, and buoyancy
• Vessel collision also a factor
In Russia
http://englishrussia.com/?m=200612&paged=5
Seismic Loads
• Induce horizontal and vertical design
• Track works as a damping agent
• Three defined levels of ground motion
Fatigue
• What most railroad are designed for!
• From repetitive stress loadings causing cracks
• Often limit designer to bolted connection
Fracture Critical Member (FCM)
• Any member where failure result in ultimate
bridge failure
• FCM are held to higher design criteria
Deflection, Corrosion and
Bearing/Volumetric Changes
• Deflection control when long span and high
strength materials used
• Use of weathering steel popular
• Bearing transfer all load from superstructure
to substructure while still allowing rotation
and translation
• Thermal Changes
Weathering Steel Bridge
Retaining Wall Loads
• Contain within the right of way
• 100 year life cycle
• Live loading envelope of track structure