CE 515 Railroad Engineering

StructuresSource: AREMA Chapter 8

Introduction and Major Bridge Components

“Transportation exists to conquer space and time -”

Introduction

• Railway structures serve one of two functions:– Support the track itself – House railway operations

• What are some examples of railway structures?

Types of StructuresTrack Carrying Structures

– Bridges– Trestles– Viaducts– Culverts– Scales– Inspection Pits– Unloading Pits

Source: http://northernsong.wordpress.com/2009/09/02/construction-and-value/

Source: http://www.nationalcorridors.org/df/df08192002.shtml

Source: http://switzerlandinview.wordpress.com/2007/10/29/landwasser-viaduct//

Types of StructuresAncillary Structures

– Drainage Structures– Retaining Walls– Tunnels– Snow Sheds– Repair Shops– Loading Docks– Passenger Stations– Platforms– Fueling Facilities– Towers– Catenary Frames

Source: http://www.gatewaynmra.org/articles/tunnel-liner.htm

Source: http://home.att.net/~berliner-ultrasonics/rr4.html

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

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

Major Bridge Components

Substructure

Superstructure

Bridge Deck

Source: http://www.michaelminn.net/america/johnstown,_pa/2008-11-05_13-23-45_corrected.jpg

Source: http://farm4.static.flickr.com/3078/3098004504_94f659cddf.jpg

Source: http://upload.wikimedia.org/wikipedia/commons/thumb/3/37/Forth_Rail_Bridge_Pier.jpg/800px-Forth_Rail_Bridge_Pier.jpg

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

Substructure: Soil and Geologic Conditions

• Structure stability is dependant on soil conditions

• Design Reference:– Chapter 8, Part 22 of AREMA Manual for Railway

Engineering

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

Bearing/Friction Piles

• Pile is driven, jetted, or otherwise embedded on end into the ground.– Timber Pile Driving Video– Concrete– Steel

Source: http://www.fhwa.dot.gov/infrastructure/tccc/tutorial/piles/pile03d.htm

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

Source: http://www.ptbppid.com/services.html

Source: http://geofoam.syr.edu/GRC_rt23a.asp

Timber Piles

• 15-20 ton capacity– 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

Timber Piles

• Wood types– 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

Source: http://www.ehansch.com/bridges.html

Steel Piles: H-Beam Sections and Tubular Sections

• Two classifications of steel piles:– Rolled “H”– Tubular sections—usually concrete filled

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

Source: http://www.roadstothefuture.com/I64-I295-Int-Mod-Photos-Nov07.html

Tubular Sections

• Typically filled with plain or reinforced concrete

• Possess large MOI, suitable to resist lateral forces

Source: http://www.geodrillinginternational.com/__data/assets/lead_thumbnail/0012/178698/Aarsleff-plead.jpg

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

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

Source: http://www.archiexpo.com/prod/samer-spa/precast-reinforced-concrete-driven-pile-61928-156368.html

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

Source: http://ci.billings.mt.us/PhotoView.aspx?PHID=233

Substructure: Abutments

• Three primary types of abutments:– Wing• Breast

– “U”-Shaped• Arch

– “T”-Shaped– Other Modifications• Buried and Hollow or Box

“Wing” Abutments

• Used when embankment is not a high fill

• Simple breast wall, flanked by wings– Wings turn back at ~30+

degrees• Modification:– Breast

Source: http://74.125.155.132/search?q=cache:25pomvsrG-cJ:chestofbooks.com/architecture/Cyclopedia-Carpentry-Building-4-6/234-Abutments.html+U-shaped+abutment&cd=3&hl=en&ct=clnk&gl=us

“U” Abutments

• Two wings that extend backwards at right angles to the face– Sometimes modified into the

“pulpit”

Source: http://74.125.155.132/search?q=cache:25pomvsrG-cJ:chestofbooks.com/architecture/Cyclopedia-Carpentry-Building-4-6/234-Abutments.html+U-shaped+abutment&cd=3&hl=en&ct=clnk&gl=us

“T” Abutments

• Similar to breast type abutments with addition of a stem– Stem stabilizes the breast– Bridges the slope of the embankment

Substructure: Piers

• Contribute intermediate support for muti-span brides

• Rest on stable, unyielding foundations below frost line

• Placed below scouring elevation

Source: http://www.artsintransit.org/pages/organizational.html

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

Source: http://www.historicbridges.org/pennsylvania/sharonrr1/

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

Open Deck Bridges

• Less costly• Free draining• Use over streets

requires additional measures

• Establishes a permanent rail elevation

Source: http://www.vwindependent.com/Stories%20for%20April%202008.htm

Ballast Deck Bridges

• Provides better riding track

• Consistent track modulus on bridge

• Reballasting concerns• Provide protection for

activities below Source: http://www.hothamvalleyrailway.com.au/news.htm

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

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 10-12 feet by 8-in x 8-14-in

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

Source: http://www.trains.com/trn/default.aspx?c=a&id=4179

Ballast and Bridge Floors

• Ballast– 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

Other Bridge Deck Considerations

• Drainage• Anchorage of Bridge Ties• Guard Timbers• Inner Guard Rails

Questions