Massive Woodrow Wilson Bridge Challenges Pumpers on Many Levels
From routine pumping of precast sections to designing delivery systems that adjust to the changing of the tides, pumping contractors Curtis Creek Concrete Pumping, LLC, Baltimore, MD, and Brundage-Bone & Blanchet, LLC, Maryland, are meeting the challenge on the new Woodrow Wilson Bridge.
In 1961, engineers and contractors completed the Woodrow Wilson Bridge, successfully carrying traffic from the Capital Beltway (I-95/I-495) over the Potomac River between Maryland and Virginia. Officials estimated the bridge would carry 75,000 vehicles a day for the next twenty years. Forty years later and three times the intended traffic have resulted in one of the worst bottlenecks in the country. In addition, the bridge offers only a 50-foot channel clearance, forcing motorists to endure approximately 250 openings every year.
In February 2001, contractors completed dredging of 340,000 cubic yards of material to make room for the $2.6 billion replacement of the existing Woodrow Wilson Bridge. Sponsoring is supplied by four cooperating agencies: the Federal Highway Administration (FHWA), Virginia Department of Transportation (VDOT), Maryland State Highway Administration (MSHA), and the District Department of Transportation (D.DOT).
At seven and a half miles long, the Woodrow Wilson Bridge Project is the largest public works project in the mid-Atlantic region, and is split into three contracts: the Maryland Approach, the Bascule Span and the Virginia Approach. Specs include replacing the existing single-span draw-type bridge with two parallel 6075-foot long bascule bridges. The new bridges will provide 20 feet more vertical clearance, and new V-shaped reinforced concrete piers will widen channel clearance by 85 feet. These combined improvements will minimize the number of annual drawbridge openings to 65. Each span will provide six lanes for vehicle traffic, full shoulders and a bike path. Four new interchanges will also improve traffic flow and alleviate congestion.
Contractors commenced on construction of both the southern and northern bridges simultaneously, with the intention of completing the southern span by spring 2006, at which point traffic will be diverted to the completed portion and the existing bridge will be demolished. Contractors are on track for a 2008 deadline of the northern bridge. Joint venture Potomac Constructors, LLC, is responsible for the construction of the 3,300-foot long Maryland approach, running 1.1 miles from the Maryland shore to the “centerpiece” of the bridge, the bascule span. Three partnering general contractors, Edward Kraemer & Sons, Hanover, MD; American Bridge Company, Coraopolis, PA; and Trumbull Corporation, Pittsburgh, PA are progressing on segment construction, segment installation and bridge deck construction.
The precast yard, also serving as the headquarters of the project site, is located on the Maryland shore. Curtis Creek Concrete Pumping provides 28 and 32-meter boom pumps and operators to pump a total 616 pier segments for the Maryland Approach. A temporary on-site batch plant allows ready mix supplier Aggregate Industries, with US corporate offices in Rockville, MD, to easily access and supply the pumps. Contractors are creating three types of segments – starter segments, “regular” or “typical” segments, and knuckle segments – utilizing a long line casting method. A complex forming system designed by EFCO, Des Moines, IA, is especially agile and features an integrated mandrel carrier. This allows contractors to adjust the size and shape as the core of each type of segment is formed. The concrete pumping company completes ten segments each week pouring twice a day, five days a week requiring the pumping contractor to be available and ready to service the customer on demand.
Each segment requires only 35 yards of concrete, but production has remained slow at ten yards per hour due to a complicated and wet 3500 psi mix. A slump between four and eight inches makes the mix very hard to control, so the company’s pumping crews are forced to utilize a very patient pumping method, pouring the narrow, vertical walls a little at a time, allowing the mix to set between pours.
The starter segments are cast in one of the precast yard’s two long-line beds and cure in the forms. These segments serve as the first block set on the pier pedestals. The regular segments serve as the legs of the “V piers, and are cast using a strictly measured match-cast casting method utilizing the long-line beds. Each pier increases in size as they move across the river, so no two regular segments are cast the same way. The most complex of the three, the knuckle segments, measure about 20 feet wide and require a rebar skeleton weighing in at 18,000 pounds. These segments are transported by barge and installed on top of the piers.
Once the segments are cured and contractors are prepared for their arrival at the bridge site, the segments are removed from the forms using a shuttle lift with a carrying capacity of 120 tons. Segments are craned to the staging area, then lifted onto a barge, and finally transported by barge to the pier. The typical segments are erected using a Manitowoc 4100 and a specially designed piece of equipment called a manipulator. The manipulator rests on the previously erected segment and then clamps onto the next segment in sequence. A remote control manipulates an iron arm along the axis until it is in place.
Construction of the Maryland Approach’s “V” piers will continue throughout most of 2005. To construct the bridge deck, Lyell Tripp, Project Manager with Edward Kraemer & Sons, says the construction team will utilize a 32-meter separate placing boom supplied by trailer pump. The team will also incorporate a powered deck placer, which will be supplied by a concrete boom pump and/or trailer pump and run on pipe rails.
Work is also moving along on “V” pier construction on the bascule span, the “centerpiece” of the Woodrow Wilson Bridge. American Bridge and Edward Kramer & Sons, AJV oversee this contract. The concrete pumping company provides an intricately engineered system of pumps, supply line and placing equipment for the construction of the pier legs.
Despite being much smaller in size, the contract value of the bascule span is just shy of the of much larger Maryland Approach contract. The hefty price tag can be attributed to the construction of the spans’ “V” piers. Although aesthetically similar to the approach piers, crews are utilizing the cast-in-place segmental method to create stronger piers. Three massive V-piers will support each pair of the bascule’s four, 3.5 million pound steel draw spans.
Each segment, requiring approximately 150 cubic yards, is similar to a large box culvert. The segments are hollow on the inside, bending outward at a 45-degree angle, and consist of two separate components, a floor with two short stem walls, and a top that combines the web walls and ceiling. For each pour, the team uses forms supported by an intricate falsework system designed by Janssen & Spaans Engineering, Inc. Indianapolis, IN. The falsework operates using a sandjack system, which is easily maneuvered once pours are completed.
Two Schwing separate placing booms place concrete into the formwork from centrally located, free standing towers. The bases on both towers are ballasted with a 16-foot square concrete block, which can be broken down to five pieces, the heaviest weighing approximately 120,000 pounds. In order to supply the booms with concrete, contractors engineered an intricately designed line system.
Both booms are supplied through separate 900-foot and 1300-foot long floating slickline from a high pressure trailer pump set up on the shore. Crews support the system on barges that run out to work platforms fixed in place to the Potomac River bottom.
A tide varying as much as four to five feet each day provided contractors with a big challenge, as movement of the system could create interruptions to the concrete delivery. The solution was provided by designer Ray Musselman and Conforms, Port Washington, WI, with a pipe that is capable of automatically compensating for the change in tide with swivel elbows. Removable ballast blocks along the slickline are equipped with quick-disconnects. The system also has an environmentally friendly blowback capability to prevent spillage into the river.
Ready mix access to the line pump is over one of the busiest, most congested roads in the country. The mix needs to be forgiving as an unexpected traffic jam on the existing bridge or elsewhere on the roadway leaves the pump without fresh concrete for up to an hour. A 6.5-inch sack mix with 50% fly ash and high range water reducers provides a life span of over two hours without loss of final strength or workability.
The booms are utilized to place concrete into the piers once or twice each week. They will place a total 33,000 cubic yards of concrete over a two-year period.
The boom towers are centrally located as crews progress on construction of the south span piers. Once the south span work is completed, the booms and towers will be relocated to concentrate efforts on the north span.
The third section of bridge construction runs from the Virginia shore to the bascule section. Corman Construction, Inc., Annapolis Junction, MD, and Granite Construction, Watsonville, CA created the joint venture Virginia Approach Constructors. Projects on this portion of the bridge include bridge deck construction, construction of segments, and segment installation. Pumping contractor Brundage-Bone & Blanchet, LLC, Maryland, are supplying pumps and operators for precast work and bridge deck construction.
The complete Woodrow Wilson Bridge project is on track for completion in 2006. Completion on all supplementary work, including on-shore interchanges is projected for 2011.