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By Howard Ande
Heavy coal and grain trains, more frequent passenger-rail traffic, extreme temperatures, and rain, snow and ice are taking a toll on rail bridges. Decades of service are compromising their condition, as well. Many U.S. rail bridges are close to or more than a century old.
With bridges and trestles continuing to age and wear out, there's a growing need to rebuild or replace many of them. So, railroads are pursuing projects designed to do just that.
Hundreds of bridges are monitored by Norfolk Southern Railway engineering department officials, who maintain an inventory that includes a description of each bridge. All bridges are inspected at least annually, condition is recorded and performed maintenance is logged. The Class I's bridge program typically involves many projects performed simultaneously.
"Approximately 100 bridge projects in the rehab or construction phase are going on at all times on the system," says NS Chief Engineer of Bridges and Structures Jim Carter.
Each year, NS tries to replace timber trestles, many of which are up to 70 years old. The trestles typically are replaced with ballast deck precast, prestressed concrete and box girders mounted on pipe pile filled and capped with concrete, says Carter.
Emerging technology could play a role in future bridge projects, such as a hybrid composite beam (HCB), he says. Comprising a carbon-fiber reinforced concrete arch encased with fiberglass, HCB is undergoing tests at the Transportation Technology Center Inc.'s Facility for Accelerated Service Testing (FAST) track in Pueblo, Colo. The beams might begin entering the mainstream as an option for bridge work, but for now, NS has no plans to use HCB in revenue service, says Carter.
"We are following the FAST test," he says.
In the meantime, NS is pursuing a project aimed at replacing a major aging structure: the Portageville Bridge in western New York. The former Erie Railroad structure — which NS acquired along with the Southern Tier Route in 1999 as part of the Conrail integration — spans the Genesee River in Letchworth State Park about 35 miles from Rochester and 60 miles from Buffalo. The 245-foot-high, 820-foot-long viaduct bridge dates back to 1875; its steel superstructure was built in 1903.
The pin-connected deck truss and deck plate girder bridge is an example of "very light construction" from a bygone era, when railroad managers didn't envision 286,000-pound freight cars, says Carter. Currently, there's a 10 mph speed restriction and 273,000-pound car weight limit on the bridge instead of more typical 35 mph and 286k limits.
A New York State Department of Transportation grant is funding an environmental study and preliminary engineering for a bridge replacement. Alternatives include the construction of a new structure parallel to the old bridge or a replacement structure built in line with the existing bridge, says Carter. The project is estimated to cost about $35 million, and options for public partnerships are being explored, he says.
"Since there is public money involved in the [bridge] design, we will not be able to complete the design until the environmental review is complete," says Carter. "We anticipate the completion of design late next year."
Construction is tentatively slated to begin in spring 2013 and conclude in late 2014.
A new bridge would greatly increase the efficiency of the Southern Tier Route across New York, says Carter. The speed and weight restrictions would be lifted, making the line a more viable route, he adds.
Union Pacific Railroad is anticipating operational efficiency gains from a major bridge replacement project, as well. The Class I plans to replace a 103-year-old, 890-foot-long structure spanning the Mississippi River on the Overland Route in Clinton, Iowa. The double-track, steel through-truss swing span bridge is a major choke point on the route, which accommodates up to 65 freight trains daily and is used to haul about 140 million gross-tons of cargo annually, UP officials said in an email.
During a 24-hour period, the swing span might be open a cumulative total of five hours to accommodate barge traffic during the peak river shipping season; barge traffic has priority over rail traffic.
This swing span bridge is obsolete, with a horizontal bridge opening of only 177 feet — well short of the 300-foot minimum now required by the U.S. Coast Guard, UP officials said. In addition, the bridge has been struck by river barges and watercraft more than 100 times in the past 15 years, they said.
To alleviate problems associated with the antiquated structure, the Class I proposes to build a new clear span bridge, which would "greatly increase river traffic safety and eliminate a railroad bottleneck," UP officials said. Project details still are being finalized and a construction schedule has not been determined.
Because the bridge's design calls for a clear span, longer approaches will need to be employed to gain the necessary elevation over the river, UP officials said. The new bridge, along with other nearby projects — including a new crew change facility — will bring the total investment in the area to about $400 million, they estimate.
A short line already is investing capital in a bridge project, to the tune of $500,000. New York, Susquehanna and Western Railway Corp. (NYSW) crews are beginning to upgrade a bridge near Ridgewood and Midland Park, N.J., that retains a 25 mph speed restriction.
The project is an example of an alternative method to bridge replacement or rehabilitation, according to NYSW officials.
The 83.5-foot-long, double-track, through-plate girder bridge was built on two abutments in 1913 and carried tracks over a long-abandoned trolley line right of way.
Instead of building a new bridge, crews will employ an earthen fill and drainage pipe method. To complete the project, 225 linear feet of ballast and track will be installed on top of the fill, which will be graded to the same level as the tops of the old abutments. As of press time, work was slated to begin late last month or in October.
Bridge maintenance no longer will be required and the railroad will register locomotive fuel savings because the speed restriction will be eliminated,
according to NYSW officials.
Meanwhile, Alaska Railroad Corp. (ARRC) is using alternative materials to rehabilitate existing timber bridges. The freight and passenger railroad is beginning to use 10- by 18-foot laminated stringers in place of increasingly hard-to-get sawn timber, says ARRC General Bridges and Buildings Supervisor Allen Price.
"It is anticipated that the laminated stringers may have a longer lifespan due to more thorough preservative penetration," he says.
Replacing timber structures is a priority because ARRC has 155 bridges on its system — many of which are advancing in age — that total about five miles in length if placed end to end, says Price.
An $800,000 project completed in spring typified the ongoing effort: the replacement of the 140-foot Ship Creek timber bridge, which was built in the 1920s. The project included the replacement of the timber bents with steel piles and caps, and replacement of standard timber bulkheads with sheetpiling.
ARRC typically budgets $3 million to $4 million annually for bridge projects. Programmed replacement of timber bridges and foundation elements includes replacement of timber piers and towers utilizing steel and/or concrete. Concrete ballast deck spans are used extensively to replace timber spans where height is sufficient, says Price.
In addition to the bridge program, two large capacity expansion projects on ARRC's slate this year include bridge work: the Northern Rail Extension Project (NREP) and Port MacKenzie Rail Project (PMRP). The NREP calls for completing an 80-mile line extension from a terminus near North Pole to near Delta Junction, Alaska.
The project involves the construction of a major bridge over the Tanana River.
To be completed in 2014, the PMRP includes the creation of a 32.5-mile rail corridor to serve deepwater facilities at Port MacKenzie and work involving a number of bridges.
Several passenger railroads and transit agencies also are pursuing bridge projects as part of efforts to expand capacity.
For example, the Tri-County Metropolitan Transportation District of Oregon (TriMet) plans to construct the Portland-Milwaukie light-rail bridge over the Willamette River in Portland, Ore., as a component of the nearly $1.5 billion, 7.3-mile MAX light-rail expansion project slated for completion in September 2015. Construction on the bridge began July 1.
The first bridge to be constructed over the river in more than 40 years, the 1,720-foot cable-stayed structure will accommodate light-rail trains, buses and future streetcars. About 100 million people use Portland's public transportation system annually.
However, the area's wildlife is a major consideration for the project, as well, TriMet project managers say.
"A unique challenge in the construction of this bridge is to consider the environment of a variety of steelhead trout, salmon and green sturgeon protected under the Threatened and Endangered Species Recovery Act of 2005," says Project Director Rob Barnard.
To address it, the agency plans to rely on a "fish window" running from July 1 through Oct. 31, 2011, that allows in-river work to build two 70- by 110-foot sheet pile coffer dams, which will prevent further disturbance of the river bottom. To be accessed by temporary bridges from both shores of the Willamette River, the dams will accommodate construction of the bridge's two towers.
After the dams are completed, work can proceed when the fish window expires. As an extra deterrent, crews applied a layer of sand on the river bottom in the construction area.
Agency officials also considered the bridge's visual impact on the cityscape and riverfront. So, support cables will run directly through the two towers using a saddle system instead of being attached by anchors to the towers, resulting in a slimmer and shorter tower.
"This means the bridge will blend in more with the urban complex, as well as save on construction material costs," says Barnard, adding that tower height will be reduced to 186 feet from the 254- and 277-foot heights if an anchor system had been used.
While TriMet builds a new bridge on the West Coast, MTA Long Island Rail Road (LIRR) continues to revamp an old bridge on the East Coast.
LIRR is upgrading the Atlantic Avenue Viaduct in Brooklyn, N.Y., which accommodates trains carrying 25,000 passengers each weekday between Jamaica Station and the Atlantic Terminal.
The two-track, 8,500-foot-long viaduct was built in 1901 and features 199 spans. The bridge has undergone an almost complete rehabilitation since contractor Kiewit Corp. began the first phase of the project in 2008, which involved 86 spans.
Although technically a rehabilitation project, the work is closer to a full replacement because 189 spans will be changed out by the time the third and final phase is completed, according to LIRR officials.
Spans are being replaced from the midpoint of the viaduct's support columns. Work includes longitudinal and cross girders, decking, walkways, ties and rail. The railroad has employed a "unique" modular approach and used disc bearings to replace rigid bolted connections, according to LIRR officials.
"The key to the success of this project was that the replacement spans were prefabricated at an off-site location," says Rich Oakley, assistant chief program officer in LIRR's program management department, adding that the technique enables old spans to be removed and replaced quickly.
During a key stretch of the project, train service was maintained at all times by keeping one of the viaduct's two tracks operational. Most span replacement work was performed on weekends when there was less traffic. An average of eight spans were replaced each weekend, with a high of 12 spans replaced during some work periods, while rails were reinstalled at the end of the work window to be ready for the start of the Monday morning rush hour.
The original plan called for work to be performed over 104 weekends, but "in actuality, only 56 were needed," says Paul Dietlin, a director in LIRR's program management department.
Funding from the New York Metropolitan Transportation Authority's capital program, Federal Transit Administration grants and federal stimulus dollars are covering the project's $197 million cost, which might be trimmed to about $182 million, according to Oakley and Dietlin. The project received the 2011 Design-Build Project of the Year Award from the Metropolitan Section of the American Society of Civil Engineers.
Kiewit soon will be revamping old viaducts in the nation's midsection, as well. The contractor will replace three more than 100-year-old viaducts with new steel structures along the Chicago Transit Authority's (CTA) Purple Line in Evanston, Ill.
The $10.3 million project also includes new foundations, abutments, retaining walls, and water control and drainage systems. A firm construction timetable has not yet been determined for the project, according to the CTA.
The old viaducts have retained speed restrictions because of a century's worth of crumbling from train vibrations and exposure to Chicago's extreme hot and cold weather, according to the agency.
The new viaducts will enable the Purple Line to provide more efficient and faster transit times; last year, more than 10.9 million riders used the line, making it the CTA's sixth-busiest route.
Because transit agencies continue to project ridership increases driven by steadily increasing gasoline prices and freight railroads continue to anticipate more traffic after the economy finally strengthens, bridges figure to take more poundings in the near term.
Keeping structures in tip-top form ahead of any significant traffic increase figures to remain a primary engineering goal for most railroads.
Howard Ande is a Bartlett, Ill.-based free-lance writer.