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Acela Express
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| Acela Express |
Recent railway upgrades for Amtrak utilize concrete for crossties, turnout ties, bridges, station platforms, catenary foundations, and retaining walls on its Northeast Corridor Line.
Amtrak's Acela Express Service between Boston, Massachusetts and Washington, D.C., on the Northeast Corridor Line, utilize locomotives and trains manufactured by a consortium of Bombardier and ALSTOM. The trains operate at a top speed of 150 mph, reducing the trip between Boston and New York to 3 hours and between New York and Washington to 2 hours and 45 minutes.
In order to accommodate the high speed trains, the entire line between Washington and Boston was revitalized, including track, signals, electrification, maintenance facilities, rail yards, bridges, and several stations.
The Acela Express passenger cars provide a smooth comfortable ride by employing computerized tilt technology to neutralize passenger discomfort as the train negotiates curves at high speed. Electrification is being extended on the Northeast Corridor Line from New Haven, Connecticut, to Boston, so that the entire line will be electrified. Each trainset will have two 6,000 hp power cars and six coaches, and will accommodate 304 passengers.
Acela (a combination of "acceleration" and "excellence") offers passengers new luxuries such as plush seats with footrests and adjustable head cushions, outlets for laptop computers, and personal audio programming. Acela is designed to lure commuters back to the railways with features like a new pub-style café with updated menu, beer on tap, gourmet coffees, television monitors, and new rest rooms featuring large backlit mirrors, shelf space, and diaper-changing tables. Business travelers have the extra incentive of thirty-two conference tables throughout the train and public telephones.
Crossties Hold the Gage
High speed operation of the Acela Express Service depends on engineering the track and vehicle as one system. After determining the optimum interaction between cars and track, Amtrak's engineers decided on the required upgrades for the existing track to satisfy the high speed design. High speed operation depends on a stable track system including rail, ties, ballast, subballast, and subgrade.
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| Track Laying Machine |
Amtrak's high speed track will be capable of accommodating trains at speeds of 150 mph, meeting the FRA requirements for Class 8 track, per Track Safety Standards Part 213, dated September 21, 1998.
For track improvements, Amtrak engineers specified 136 lb welded rail and trap rock ballast, both Amtrak standards. The engineers selected concrete ties for the high speed line because of the concrete ties' mass, stiffness, excellent ability to hold the track gage, and long life. Amtrak started using concrete ties for their heavier service lines in 1976 and now have 3 million concrete ties in use.
Concrete ties provide more mass than timber ties because the weight of a concrete tie is 760 lb to 800 lb, while the weight of a timber tie is only about 400 lb. Concrete ties are stiffer than timber because of concrete's higher modulus of elasticity (about 3:1) and the fact that the concrete ties specified by Amtrak are slightly larger than timber ties. Also, the larger concrete ties engage more of the ballast. Since the rail clip is anchored to very strong concrete (7,000 psi) the clip's ability to hold the track gage is superior, and has been proven by Amtrak's experience.
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| Concrete Crosstie |
The initial cost of concrete tie systems is competitive with tie systems of other materials and offer an overall cost advantage because concrete ties are expected to last 50 years, while timber ties would only last 25 to 30 years on the Northeast Corridor. In addition, concrete ties are spaced at 2'-0" centers by Amtrak, while timber ties are spaced at 1'-7 ˝" centers, reducing the required number of ties by 18%.
In 1982, Amtrak developed a technical specification for concrete ties and rail fasteners. The specification contains comprehensive requirements and acceptance testing for ties and rail fasteners.
Installation of concrete ties has now become routine. Amtrak's TLM (track laying machine) can lay 3600 to 4400 feet of track per day with concrete ties. The Pandrol rail clips specified by Amtrak come preinstalled on the ties. Fastening the rail to the tie requires that the clip be closed after the rail is laid on the tie. The railroad installs inner guard rails on existing concrete ties at designated bridges by using field installed inserts and bolts.
Concrete crossties are also used by Amtrak for high speed turnouts and crossovers. The railroad purchases the entire turnout including rail, steel, and ties from one source that will prefabricate the turnout into subassemblies and will guarantee that all parts fit together. Amtrak uses a number 32.75 turnout for 80 mph diverging speed and other turnouts for lower speeds. The largest turnout is 500 feet long and requires seven cars to ship the turnout from the fabricator to the site.
Fast Bridge Renovation
The railroad also renovated 90 bridges along the Northeast Corridor. Many of the bridges consist of timber ties mounted on the top flange of steel girders (open deck girder bridges). For bridges where the structural steel was in good condition, the timber ties were removed and replaced with precast panels in the shape of a trough to convert the deck to a ballasted deck bridge.
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| New precast bridge deck |
Structural engineers made thorough condition evaluations and rated the bridges to ensure that the existing steel beams can support the E80 and additional loads of the ballasted deck. For a typical 60 foot span, reinforced concrete panels 13 feet wide by 8 feet long were precast at Amtrak's Wilmington, Delaware plant, shipped to the work site and erected by Amtrak crews.
For bridges where the structural steel needed replacement (about 56 of the 90 bridges), the entire bridge superstructure was replaced with a trough-shaped precast panel made from longitudinal steel wide-flange beams spaced about 1 foot-3 inches apart and encased in concrete. The new 13 feet-6 inches wide ballasted deck bridge was normally precast in two longitudinal halves because of crane lift limitations.
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| Bridge superstructure replacement |
Only one track at a time was taken out of service for the bridge superstructure and deck replacement. Necessary repairs to masonry or concrete piers were performed prior to erection of the new bridge. In addition, walkways consisting of galvanized grating and handrail on light steel framing were erected and attached to the concrete bridge. Amtrak has used the ballasted deck method of replacement since 1979 because it is easier to maintain and surface track that is supported uniformly by ballast along the track.
The railroad expects the new decks and bridge superstructures will have a fifty-year life and will require little maintenance.
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Route 128 Station (Westwood, MA)
Architect/Engineer: Frederic R. Harris, Inc., Bellevue, WA
Contractor: Perini Corporation, Framingham, MA
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Durable Station Platforms
Because the new passenger cars have only high-level entrances, several stations required new platforms. At the Route 128 Station near Boston, two new platforms of precast double tee sections were constructed to replace the existing low level platforms. At Wilmington, Delaware, and Baltimore, Maryland, the 30 year old platforms were replaced with precast concrete beams and deck slabs. The deck slabs were cast with an integral ADA compliant tactile edge. Precast concrete was used for these platforms because of durability, ease, and speed of construction. Since the stations were in operation, existing platforms had to be demolished and the new platforms constructed in carefully phased operations.
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Wilmington Station (Wilmington, DE)
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Baltimore Station (Baltimore, MD)
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Architect/Engineer: Bergmann Associates, Philadelphia, PA
Precaster: Superior Precast, Inc., Pottstown, PA
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Catenary Support Foundations
Amtrak electrified the mainline Acela track between New Haven, Connecticut and Boston, Massachusetts (a distance of 156 miles), by adding catenary conductors for each of the two tracks. The catenary support poles are approximately 31 feet high and are bolted to concrete pier foundations. Most of the piers are precast reinforced concrete, approximately 20 inches in diameter and about 17 feet long. Four or more anchor bolts for attaching the poles to the foundations are cast into the concrete.
Typically, the concrete piers were precast off site, shipped to the work area, and then placed into preaugered holes. Grout was pumped through pipes cast in the concrete to the bottom and sides of the pier to fill any voids that existed between the pier and the soil. Because the soil conditions varied greatly (sand, silt, clay or rock) along the route, several types of piers were precast. However, where piers larger than 42" in diameter were required, cast-in-place concrete was used for the pier foundations. The electrification work required approximately 14,000 foundations.
Aesthetic aspects of constructing the line were very important. To improve the appearance of the new installation, the elevations of the top of the catenary support piers are kept at the same elevation as the top of the rail.
Heavy-Duty Retaining Walls
Development of new maintenance facilities for the high speed rail equipment necessitated construction of retaining walls at both the Washington, D.C. and Queens, New York sites. The wall in Washington is approximately 1,000 feet long and consists of galvanized H-piles with precast concrete panels. The heavy-duty design permitted rapid construction and allows for the installation of a future track adjacent to the top of the wall. The 500 feet long wall in Queens was quickly constructed using the DoubleWal system.
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Ivy City Retaining Wall (Washington, DC)
Precaster: Terre Hill Concrete Products, Inc., Terre Hill, PA
Contractor: Buch Construction, Inc., Laurel, MD
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Sunnyside Wall (Queens, NY)
System: DoubleWal Corp., Plainfield, CT
Contractor: Railroad Construction Company, Inc., Paterson, NJ
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