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At-Risk DC Bridge Gets New Support Plan

Thursday, April 21, 2016

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With time running out to raise funds to award a contract to restore a historic Washington, D.C., bridge, the National Park Service has floated a plan that would keep the crossing open, even during its much-needed rehabilitation.

The Arlington Memorial Bridge, which serves as a symbolic entry to Washington, D.C., underwent a Federal Highway Administration inspection in February that found the structure to be in considerably worse condition since its 2015 assessment, and that wear and tear is worsening at an accelerated rate.

Arlington Memorial Bridge
© iStock.com / amedved

A National Park Service proposal offers an alternative to fully closing the Arlington Memorial Bridge for rehabiliation that will also save money on the project, according to the agency's presentation materials.

At that time, the NPS (which manages all U.S. national parks, many American national monuments, and other conservation and historical properties) estimated that it would take $250 million in necessary repair and renovation costs to keep the span functional, but without attention to the decking and support structure, the bridge could close to traffic in 2021.

Now, documents filed with the National Capital Planning Commission, the federal agency charged with providing planning guidance for Washington, D.C., and the surrounding area, suggest the NPS favors an alternative plan to replace the severely corroded bascule (or drawbridge) span with variable depth girders, the Washington Business Journal reported Monday (April 18).

Such a move is expected to save $30 million versus the costs required to rehabilitate the bridge. Additionally, this approach would not require full closure of the bridge, which the NPS estimates would save $12 million in travel delays for the 68,000 vehicles that use the bridge on a daily basis.

Weighing Alternatives

According to the NPS submission materials, the agency has identified four options for restoring the bridge, one of which is the original rehabilitation strategy.

All four plans include:

  • Repair of bridge piers, foundations, and bearings;
  • Repair of concrete arch spans;
  • Replacement of bridge deck and expansion joints;
  • Replacement of sidewalks and repair of curbs;
  • Repair of non-structural elements such as balustrades; and
  • Stone to be repointed and cleaned, replaced if required.
Current conditions of Memorial Bridge
National Park Service

While rehabilitation of the bascule section of the bridge was the original plan, that was no longer feasible after the structural steel in that section was found to be deteriorating at a much faster rate than expected, the NPS said.

The plans diverge with the following alternatives:

  • Alternative 1A - Replace the bascule span with concrete beams;
  • Alternative 1B - Replace the bascule span with variable depth girders;
  • Alternative 2 – Replace the bascule span with fixed steel truss; and
  • Alternative 3 – Rehabilitate the existing bascule span.

Rehabilitation Risks

While Alternative 3 was originally the preferred option, as rehabilitation of the bascule span would best keep the span’s historic features, the spring 2015 inspection raised concerns about its feasibility, NPS explains. That assessment showed the structural steel trusses in the bascule section of the bridge to be deteriorating at a much faster rate than expected and much of the steel could not be reused. Many areas, NPS said, show 80 percent to 100 percent loss of steel.

Moreover, any steel retained from the original structure, at 80-plus years of age, would deliver a shorter life expectancy, requiring another rehabilitation “decades sooner” than if the bascule were replaced.

The NPS also pointed out that pack rust between connected steel plates is difficult to detect, correct and prevent and would likely lead to costly change-orders and accelerate the need for future repairs.

NPS preferred alternative
National Park Service

NPS's "preferred alternative" is to replace the bascule span with variable depth girders, allowing the bridge to retain historic features while also solving issues that led to the current bridge's rapid deterioration.

Finally, “retaining the structure would mean retaining some of the shortcomings of the original design that have led to the bridge’s rapid degradation,” the agency noted.

Preferred Alternative

The NPS has identified Alternative 1B, replacing the bascule span with variable depth girders, as its preferred alternative.

This option would enable the bridge to retain many of its “character-defining features,” such as the abutments, fascia, railings, light posts, and guard and overseer cabins, and the system would also mimic the arch of the original trusses.

It also solves several issues that led to the deterioration of the existing span. For example, the NPS indicates the new bridge deck would be constructed with a continuous slab, thereby removing the drainage issues at the roadbed-sidewalk joint that eroded the underlying steel.

The new variable depth structural steel would also be fully accessible for routine maintenance and inspection, as well as easier to paint than the existing truss system. In fact, the agency points out, operation and maintenances costs over the life of the bridge would be $40 million less than they would be for the rehabilitation.

The NPS will present its proposal to the NCPC on May 5.

In the meantime, the agency is undertaking the required Environmental Assessment to examine the potential environmental impacts of the project. The EA is now open for public comment through May 16.

   

Tagged categories: Bridges; concrete; Federal Highway Administration (FHWA); Historic Structures; Infrastructure; Rehabilitation/Repair; Renovation; Roads/Highways; Structural steel

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