Concrete

Comments

Transcription

Concrete
Chapter 23
Concrete & Other
Artificial Ties
Types of ties
Timber
Plastic (and composite)
Concrete
Steel
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• Concrete
– Early Use
• Problems (not pre-stressed)
– After World War II
• Pre-stressed Designs
• Revised Specs
Concrete Cross Ties (Monoblock)
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Precast, pre-stressed concrete
Effective for high tonnage or high speed track
Elastic fastener systems of various designs
Vulnerable to mechanical damage, rail seat abrasion,
effects of poor subgrade
• Must insulate in track circuit territory
Typical Concrete Tie
~ 2 1/2 times heavier than wood ties,
More expensive than wood ties
Pre-cast, Pre-Stressed, elastic fastenings embedded
Tie Manufacturer
Highway Crossing
Surface
Turnout
• Fastenings
• Recent Experience
• Economics ???
Some Problems with Concrete Ties
Epoxy Repair of Concrete Tie Rail
Seat Deterioration
Wear and Abrasion
Pumping Track (stiffer track compared to
wood tie track, need quality support for
concrete tie track)
Concrete Tie Pads
• Recent Experiences with Concrete Ties
– Need high-quality subgrade for support
– Pressures on ballast are higher under concrete ties
compared to wood ties
– Concrete tie track produces stiffer(higher
modulus) track compared to wood tie track
– Rail-Seat abrasion and insert problems
AREMA Manual
• Performance Specifications
• Tie Spacing – wider than wood ties
• Tie Dimensions – slightly larger than wood ties
• Load Distribution – higher ballast pressure
• Impact Factor – higher than for wood ties
• ≈55%
For 27-inch
tie spacing
• Ballast Pressure
• Subgrade Pressure
• Lateral & Longitudinal Loads
• Rail Flexure
• Concrete Properties – very high strength
• Pre-tensioning Tendons – typically 270 kip
• Tie Pads -- important
• Steel
• Two-Block Concrete/Steel
• Plastic
Steel Ties
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Rolled channel shape with downturned ends
Elastic fastener systems of various designs
Track stiffness comparable to timber ties
Poor for wet or corrosive environments
May abrade soft ballast materials
Alternate Concrete Tie
Two-Block
or
Bi-Block
With
Steel Beam
• Reconstituted/Laminated Wood
• Slab Track
• Azobe & Mora Wood
• Plastic
Concrete Slab Track
Direct Fixation
Ballastless Track
Azobe Hardwood Ties
Plastic Ties
• Attractive in areas where timber is decay prone
• In-track behavior similar to timber
• Compatible with timber tie handling and installation
equipment
• Compatible with fasteners used for timber
• Pre-drill fastener holes to avoid splitting tie
First Steel Reinforced Plastic Bridge Ties installed in American railroading.
Bridge P 424.8 Leeds, AL May, 2005 Manufactured by Plastic Pilings.
An additional 1000 ties will be installed in 2006
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BURKE PARSONS BOWLBY PARRALAM DECK
LUMBER CITY, GA
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