A Wilson with one important point
During his final coherent days in office, the 28th President of the United States was in the midst of a tour of the country when he turned to an advisor and said, "I think I’m falling to pieces." Another Woodrow Wilson couldn’t be built back then.
Now the time has come to make one stronger, bigger and on the cutting edge. A second Woodrow Wilson Memorial Bridge is set to spread across the Potomac River, connecting Virginia and Maryland. The original Woodrow Wilson span, which carries Interstate 95 and the Capital Beltway, is starting to buckle under intense traffic over the past decade. The bridge was built to handle 75,000 vehicles a day. It’s currently feeling the tread of 175,000 daily, and projections go as high as 300,000 by the design year of 2020.
"There is an additional schedule aspect to this project in that the feeling is if they don’t move traffic off the existing bridge by somewhere around 2004 they’re going to have to look at some fairly hefty costs involved in doing some rehab," Richard Cary-Brown, vice president and principal project manager for Parsons Transportation Group Inc., told ROADS & BRIDGES.
The Parsons Transportation Group certainly knows the feeling of trying to make the new plans come to life. They submitted the winning design, which was unveiled at the 16th Annual International Bridge Conference held June 14-16 in Pittsburgh.
"We were certain we had something unique, that it was a solution," Serafim Arzoumanidis, chief designer of the bridge, told ROADS & BRIDGES. "But you can never tell how the committees and judges will do things. We had an expectation that this design would distinguish itself."
It’s a team game
The competition took flight back in the spring of 1998, when teams submitted their qualifications, which included resumés of key individuals and information on exactly who would be in charge of the project, to the committee. The field was cut to four and the teams were then asked to submit two alternatives to the design. During a blind selection process—the entries were arbitrarily labeled A, B, C and D—advisory committees examined certain aspects, such as the historical point of view, archetectual features and constructibility. The judges involved were looking for an arch-like structure that carried aesthetic value and scored points in the constructibility catagory. Of high importance was the appearance of the bascule bridge. Teams were encouraged to integrate the bascule into the look of the span so it doesn’t appear as a separate structure. The committees rated the designs and passed them over to a selection panel, which made the creation of the Parsons Transportation Group a unanimous winner.
"The fact that these committees and judges gave us unanimous support was something that was unexpected," said Arzoumanidis. "I think the seamless nature of the bridge gave us an edge over the competition. Second, the fact that the foundations were economically a good solution to the difficult soil conditions, and the construction of this alternative was much more simplified than the others."
The Parsons plan calls for a pair of 6,000-ft-long multiple-span bridges which will contain 12 lanes of traffic. The new bridge also climbs 70 ft high, which is expected to drop the number of drawbridge openings from about 220 a year to under 70. Additional features will be two high-occupancy vehicle, express bus or rail transit lanes.
Curing a belly ache
Exactly how much could sit on the soft belly of the Potomac River, particularly where the bascule span would be placed, was a chief concern for all involved.
The worst location contains approximately 55 ft of mud, and below that is a layer of sand and clay. The first hard layer is 130 ft down, and the rock floor is at 400 ft.
"Those conditions were not helping the arch concept," said Arzoumanidis. "And because of it they thought the bascule pieces would end up being very large and very costly."
Emerging from the Parsons thought process were independent ‘V’-shaped piers and foundations that were able to pull off the "arch look" while, at the same time, efficiently disperse the forces to the river bottom. The forces in the V-pier legs are resisted by the ties at the top of the 18 V-piers. The piers are segmental post-tensioned concrete, the bascule piers will be cast-in-place post-tensioned concrete. Steel pilings driven up to 150 ft below the surface will offer support.
Steel box girders will be used for the bridge superstructure. There are two sets of V-piers per structure, and each V-pier supports two of the box girders. The design will create spans of up to 200 ft.
Diaphragms between the boxes will also be box-shaped.
"We made the depth of the boxes varying between the supports with a shallower depth in the middle of the spans, so the bridge appears to be like an arch, but the structural performance is very different," said Arzoumanidis. "We came up with a solution that is more economical in terms of the foundations, when compared to a typical arch structure.
"We thought the steel box girders would make the whole structure lighter, and that would also be helpful to the foundation situation."
Parsons also thought it had a very practical way to construct the bridge deck. The original idea was to precast the segments of the deck, then ship the pieces to the sight and place them on top of the girders. However, the team later decided on a cast-in-place roadway deck, which will be transversly post-tensioned concrete. The cast-in-place alternative offered advantages in long-term durability, according to Parsons.
Money in place?
The initial price tag of the Woodrow Wilson Memorial Bridge project is $1.9 billion, with $900 million covered in the Transportation Equity Act for the 21st Century.
Legislation, however, was introduced in the summer calling for an additional $600 million for the country’s only federally-owned span.
"A lot of the members of our committee expressed concern about spending this much money in the future when there are a variety of other projects across the country that are just as desperate for improvements as the Wilson bridge is," Scott Brenner, transportation committee spokesman, told ROADS & BRIDGES. "This $900 million was the largest single earmark in the entire transportation bill, so you have members on our committee who have some very serious problems in their own states. To have to give away $900 million for this project, while it’s worthy, it’s a little hard for them to say we’re going to give you another $600 million."
The project consists of five different contracts, and includes approaches and intersections associated with the main bridge. Virginia and Maryland also will cover a portion of the final bill.
Another delay has been created by a U.S. District Court, which ordered a halt to construction of the bridge pending an environmental review.
"There’s an injunction against (the states) because the court is saying they did not follow all the normal procedures before moving ahead," said Brenner. "Right now, it’s really up to the states to figure out how to get going on this thing."
According to Parsons, the first contract will be a dredging contract. Work is expected to begin in the spring of 2000. Foundation contracts should start in the fall of 2000. A contract for the superstructure will follow, with the completion date set at 2006. Traffic could be moved to one of the bridges by 2004.
"We have our hands full right now," said Arzoumanidis. "There are so many technical issues we are working on in preparation for the final design effort. We’re at full strength right now.
"We’re very excited about this project and we think we have something that is very special."