1. CE 515 Railroad Engineering
Structures
Source: AREMA Chapter 8
Introduction and Major Bridge Components
“Transportation exists to conquer space and time -”

2. Introduction Railway structures serve one of two functions:
Support the track itself
House railway operations
What are some examples of railway structures?

3. Types of Structures Track Carrying Structures Bridges Trestles
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Track Carrying Structures
Bridges
Trestles
Viaducts
Culverts
Scales
Inspection Pits
Unloading Pits
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4. Types of Structures Ancillary Structures Drainage Structures
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Drainage Structures
Retaining Walls
Tunnels
Snow Sheds
Repair Shops
Loading Docks
Passenger Stations
Platforms
Fueling Facilities
Towers
Catenary Frames
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5. Structural Design: Loads
Dead Loads—self weight
Live Loads—traffic induced
Dynamic Loads—traffic induced
impact, centrifugal, lateral and longitudinal forces.
Environmental Loads—weather
wind, snow and ice, thermal, seismic, and stream flow loads

6. Structural Design: Railway vs. Highway
Railway structures must perform under:
Heavier loads
Live load dominates design
Longer service life
Dissimilar maintenance
Fatigue and maintenance hold much higher influence

7. Major Bridge Components
Substructure Superstructure Bridge Deck
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8. Substructure Abutments, Piers, and Foundations
Transmits loads to underlying soil:
Dead Load
Live Load
Environmental Forces
General Composition
Pile Foundations
Spread Footings
Piers and Abutments
Any combination of the three

9. Substructure: Soil and Geologic Conditions
Structure stability is dependant on soil conditions
Design Reference:
Chapter 8, Part 22 of AREMA Manual for Railway Engineering

10. Substructure: Piling Further distinguished by purpose
IE, fender piles—protect masonry structures
Capacity based on allowable stress
Established in AREMA Manual Chapter 7, Part 2
Two general classifications of piling:
Bearing/Friction Piles
Sheet Piles

11. Bearing/Friction Piles
Pile is driven, jetted, or otherwise embedded on end into the ground.
Timber Pile Driving Video
Concrete
Steel
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12. Sheet Piles
A continuous connected line of piles driven together to form a wall.
Resists lateral pressures
Timber and concrete
Tongue-and-groove construction
Steel
Interlocking
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13. Timber Piles 15-20 ton capacity Straightness of pile is critical Decay
20-60ft lengths
Splicing
Straightness of pile is critical
Crooked piles produce eccentric loading
Decay
Moist ground/submerged—immune to decay
Air exposure—decay within a few years

14. Timber Piles Wood types Two classes of timber piles:
White Oak, Cypress, and Long-Leaf Yellow Pine
Two classes of timber piles:
First Class—railway bridges
Second Class—cofferdams, falsework, temporary work, and light foundations
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15. Steel Piles: H-Beam Sections and Tubular Sections
Two classifications of steel piles:
Rolled “H”
Tubular sections—usually concrete filled

16. H-Beam Sections Rolled metal sections with wide flanges
Designed for pile loading
Strength in tension and compression
Smaller cross-sectional area
Well adapted for deep construction
Minimal displacement
Breakage immunity
Susceptible to corrosion
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17. Tubular Sections Typically filled with plain or reinforced concrete
Possess large MOI, suitable to resist lateral forces
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18. Concrete Piles: Precast and Cast-In-Place
Suitable for large, heavy structures
Very durable, also immune to decay
difficult to splice
40-50 ton capacity
10-24 inch diameter
20-60 ft length
Two classifications of concrete piles:
Precast Concrete Piles
Cast-In-Place Concrete Piles

19. Precast Concrete Piles
Driven, much like timber and steel piles
Two forms of cross sections:
Uniform cross section
If piles bear on hard stratum or act as columns
Tapered cross section
If embedded in soft material or derive support
from skin friction
Taper as much as ¼-in per foot to a minimum
8-in diameter
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20. Cast-In-Place Concrete Piles
Formed by pouring concrete into a metal shell or tube previously placed
Cannot be damaged by transport/driving
Must allow for curing time
Reinforcement necessary when subject to lateral forces
Placed as single unit
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21. Substructure: Abutments
Three primary types of abutments:
Wing
Breast
“U”-Shaped
Arch
“T”-Shaped
Other Modifications
Buried and Hollow or Box

22. “Wing” Abutments Used when embankment is not a high fill
Simple breast wall, flanked by wings
Wings turn back at ~30+ degrees
Modification:
Breast
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23. “U” Abutments
Two wings that extend backwards at right angles to the face
Sometimes modified into the “pulpit”
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24. “T” Abutments Similar to breast type abutments with addition of a stem
Stem stabilizes the breast
Bridges the slope of the embankment

25. Substructure: Piers
Contribute intermediate support for muti-span brides
Rest on stable, unyielding foundations below frost line
Placed below scouring elevation
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26. Superstructure
Portion of a bridge supporting and conveying the live load to the substructure on which it rests
Two general classes:
Steel Spans
Concrete Spans
Design governed by the
nature of the obstacle being
crossed
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27. Bridge Decks
Portion of a railway bridge that supplies a means of carrying the track rails
Two general classes:
Open Deck Bridges
Rails anchored to ties directly on the bridge floor
Ballast Deck Bridges
Rails anchored to ties supported in a ballast section

28. Open Deck Bridges Less costly Free draining
Use over streets requires additional measures
Establishes a permanent rail elevation
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29. Ballast Deck Bridges Provides better riding track
Consistent track modulus on bridge
Reballasting concerns
Provide protection for activities below
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30. Superelevation on Decks
Sloping the pile or post cut-off of timber piles
Tilting the superstructure
Framing the floor system out of level (rare)
Tapering ties along bridge
Increasing ballast depth under one rail

31. Bridge Tie Framing
Bridge ties are dapped when they contact supporting steel
Maintains alignment across bridge
AREMA Dap Recommendations:
Dap not to exceed flange width by more than ½ in.
Dap be not more than ½ in.
Ties are typically feet by 8-in x in

32. What is Dapping?
“The term "dapping" refers to a notch in a timber (or in this case, a crosstie) in preparation to receive another part of timber. Dapping is a popular practice in bridgework when railroads need to shim ties up for superelevation (when the outer rail is vertically higher than the inside rail to neutralize centrifugal force). For example, if the outer rail on bridgework is 12 inches high and the inner rail is 9 inches high, railroads can cut grooves (or dap out) in sections of the timber, allowing the height difference to taper off from the high end to the low end of the timber over the distance of the timber.” -- Sayre C. Kos
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33. Ballast and Bridge Floors
Typically 6-12 inches in depth
Bridge Floors
Concrete segmented girder spans
Creosoted timber planks and timber or steel floor
Reinforced concrete slabs
Structural plates supported by strings
Structural troughs

34. Other Bridge Deck Considerations
Drainage
Anchorage of Bridge Ties
Guard Timbers
Inner Guard Rails

35. Questions