U.S. Department of Transportation
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
This magazine is an archived publication and may contain dated technical, contact, and link information.
|Publication Number: Date: September/October 2002|
Issue No: Vol. 66 No. 2
Date: September/October 2002
The redecking of three bridges, plus minor deck repair on a fourth, along the George Washington (GW) Memorial Parkway in Langley, VA, is an informative case study of how meticulous planning, use of modern engineering techniques, and well-coordinated execution ensure that a complex construction project can be carried out without major disruptions in traffic flow.
The GW Parkway bridge project spearheaded by the Federal Highway Administration's (FHWA) Eastern Federal Lands Highway Division (EFLHD)proceeded so smoothly that it won immediate praise from the media and the traveling public. In February 2002, FHWA officially recognized the efforts of the project team, by awarding its Award for Engineering Excellence.
A key aspect of the project was the use of precast panels that helped reduce the number of days that normal traffic was disrupted to just 10 weekends, versus the several months that would have been required if the traditional technique were used.
|Condition of loop road, before construction.|
All photographs courtesy of EFLHD Construction Office
|Condition of loop road, after construction.|
EFLHD is responsible for engineering safe and environmentally sensitive roadways and bridges on some of our Nation's most beautiful land. EFLHD provides a range of transportation engineering services to Federal agencies, including the planning, design, construction, and rehabilitation of federally owned highways and bridges. The division serves 31 Eastern States, Puerto Rico, the Virgin Islands, and the District of Columbia.
One of EFLHD's principal client agencies, the National Park Service, owns and operates the GW Parkway. The parkway is a four-lane divided highway that stretches about 64 kilometers (40 miles) along the Potomac River, beginning at Mount Vernon at its southern end. The four bridges, 1.6 kilometers (1 mile) from each other, are located at the northern end of the parkway. Two creeks called Dead Run and Turkey Run are each spanned by a northbound and a southbound bridge.
The bridges were in need of repair because the decks the concrete riding surface that cars drive over had developed visible surface deterioration in some places, exposing the reinforcing steel underneath the concrete surface. The EFLHD project team evaluated concrete cores that it had taken from the decks and decided that the level of concrete deterioration was such that the best course of action for three of the four bridges was to replace the decks completely. The deck of the fourth bridge had been replaced in 1975 and was judged to be in good condition, requiring only that the existing asphalt overlay be replaced with a concrete overlay. The overlay a sacrificial layer of concrete with either latex or microsilica additives to make it less penetrable by water is intended to prevent the penetration of corrosive road salts into the reinforced deck concrete underneath.
The key problem was that the bridges are in the Washington, DC, area one of the most high-volume traffic areas in the country. The four bridges carry an average daily volume of approximately 43,000 vehicles. The National Park Service was greatly concerned about inconveniencing motorists and causing traffic delays. Shutting down the bridges for days let alone weeks was clearly not an option.
The challenge before the EFLHD team was to come up with an engineering solution and also to handle the logistics in such a way that would minimize traffic delays.
Precast to the Rescue
To speed the deck replacement, the project team decided to use a technique that EFLHD had used only once before precast panels. This technique enables the bridge deck to be cast off-site in sections or panels. The panels then are transported to the site as soon as they are ready to be inserted.
The fact that the casting is done off-site inside an enclosed building allows for better quality control. For the GW Parkway project, the bridge sections were precast in southern Virginia by Bayshore Concrete Products Corporation.
Use of the precasting technique allowed the project team the flexibility to carry out the work during lean traffic hours and not affect traffic during peak hours. "You can't adequately accommodate traffic during rush hours using conventional bridge replacement methods," says Ken Atkins, project manager with EFLHD. "You'd take out two travel lanes over a long period of time. With 2,000 vehicles per lane per hour, we needed those lanes during the rush hour."
In the traditional technique, after the existing decks are taken off, a new framework of reinforcement is tied into place and the concrete is cast on-site. "You have to place reinforcing steel, then pour the concrete in," says Keith Wong, technology coordination engineer with EFLHD. "After that, you have to wait for the concrete to cure and gain strength before you can put traffic on. At a minimum, it takes about 28 days." He adds that 10 years ago another bridge was refurbished on the parkway using the traditional method, and it took several months.
This project was only the second time EFLHD had used precast panels to replace an existing deck. EFLHD has not traditionally used precast panels in deck replacement projects for two main reasons. One is that panels have to be custom-made for each bridge, and most of the bridges that EFLHD constructs are of moderate length and do not require enough panels to make precasting the most economical alternative. "Precasting thrives on replication," says Hratch Pakhchanian, EFLHD's structural design engineer for the project."If you're only making a few non-standard pieces, it's not economical."
|Turkey Run Bridge before construction.|
|Turkey Run Bridge after construction.|
The other reason for EFLHD's limited use of precast panels is that many of the EFLHD bridge rehabilitation projects do not take place in high-traffic urban environments where the need to complete the work quickly overrides the concern over the economy of scale for precasting deck panels.
Other factors that influence the decision to use precast are the cost of transporting the precast pieces and the additional engineering that is required. However, in locations where the weather dictates a short construction season, or where concrete plants are not located within practical distance from the site, as is the case in Alaska, for example, this method is used routinely.
|Removal of the old bridge deck slabs.|
The GW project essentially presented a situation where the driving issue was the tight time available to perform the work. EFLHD realized that completing the project with minimal disruption to the traveling public was crucial. Despite the cost factor, the good experience at the GW Parkway and other projects has prompted FHWA to encourage more frequent use of this technique for high-traffic bridges.
The project team decided that the tasks of replacing bridge decks, adding overlays, and replacing railings were to be restricted to the weekends when traffic volume is relatively low. A 23-stage traffic control plan was designed that maintained one lane of traffic for each direction of traffic. During weekdays, all four lanes were kept open.
Factoring that 142 panels were to be placed and post-tensioned in stages, the project plan estimated that the entire work would span 10 weekends. The contract stipulated that a bridge could be closed for construction work on Friday at 7 p.m. and had to be reopened by 5 a.m. Monday. During this window, the construction team had to remove the deck and railing, and place the new panels, then install and tension longitudinal prestressing tendons to connect the panels so they would perform as a monolithic deck.
|Placing the new deck slabs.|
Choosing the Contractor
EFLHD chose the "competitive negotiated procurement" process to award the contract. In this kind of procurement, technical and price proposals are requested from the contractors. The contract is awarded to the most technically qualified bidder based on initial proposals received, or after negotiations are conducted to clarify any technical and pricing issues in the bids.
The procurement process involved a solicitation notice that clearly indicated that the contract would be awarded based on factors other than just price. Other factors included the time of project completion, previous performance of the contractor, and the construction methodologies employed.
For the GW Parkway bridges, EFLHD had to find a contractor with the capabilities and proven track record to deal with such a complex and time-critical project. The value of the construction contract was $4.2 million.
EFLHD evaluated the resulting bids using established criteria price, time, method, and experience followed by interviews with the top three bidders. The evaluation panel consisted of EFLHD officials along with a Park Service representative. The contract was finally awarded on a "best-value" basis to Shirley Construction of Newington, VA.
|Placing latex-modified concrete overlay.|
Partnerships and Coordination
To help ensure a smooth working relationship among the various organizations, a partnering charter was developed and signed by the National Park Service, FHWA, and the contractor. The on-site EFLHD project engineer held weekly meetings to discuss project issues and potential problems, ensuring that all parties were aware of what had to be done. Minutes were kept with a "to-do" list.
The partnership approach was crucial in ensuring good communication, teamwork, and cooperation among the organizations. "It minimized unforeseen issues," says Ramesh Kotadia, assistant construction project engineer with EFLHD. "There was a detailed scheduling process for the critical weekend work. We'd reach agreement with the contractor on what work they'd be doing each weekend. We gave them a traffic control scheme to sequence the whole thing. Bridge deck replacement first, overlay, stagger, and so on."
EFLHD's construction team, the National Park Service, the contractor and subcontractors, and the Park Police all took part in the weekly meetings. Since the project involved time-bound operations every weekend, the participants discussed the following weekend's operations including the types of shutdown and preparatory activities during weekdays. "Staying in close touch with weekly meetings was absolutely essential," says Atkins. "This was particularly so, because time was the critical thing. We can't afford to have things drag on in this type of project."
The planning and coordination clearly paid off. The construction activity, which began on April 17, 1998, and was completed on June 29, 1998, was completed in the 10 weekends as scheduled. The overall costs associated with the preliminary engineering (PE) and construction engineering (CE) accounts were under budget. The final PE for the project was 9.9 percent of the construction contract (target value: 10 percent). The final CE was 10.9 percent (target value: 12 percent).
In the crucial area of customer satisfaction, the project scored a 90.3 percent (target value: 85 percent) on the completed project survey for those directly involved in the process and an average of 88.6 percent (target value: 85 percent) on the project development survey.
Keeping the Public Informed
Another key aspect was the use of a variety of communication tools to keep the public informed before and during the construction. A brochure was distributed to local businesses, hospitals, colleges, regional and local newspapers, and news associations within a 40-kilometer (25-mile) radius to inform them of the upcoming construction work, including the times and places of lane closures. In addition, weekly updates were added to EFLHD's Web site, which was linked to the Intelligent Transportation Systems of SmarTraveler®. This linkage enabled motorists to log on to the SmarTraveler Web site and find out the work and lane closures scheduled for the coming week.
FHWA also met with local radio stations and the Virginia Department of Transportation to provide a summary of the project. Radio stations were updated about the schedule of work and lane closures. In fact, Bob Marbourgh, a radio personality with WTOP, gave the project high praise during a Park Service media meeting.
Advance warning signs let drivers know that they could take alternate routes. Naturally, some inconvenience to the traveling public is inevitable when any construction work is carried out in such a high-traffic zone. But by issuing advance notices and information, the team helped reduce delays for commuters. The lack of major traffic backups during the entire project was testimony to good planning and coordination. According to Park Superintendent Audrey Calhoun, "[The work] was done with minimum disruption to the public, and I don't believe that we received any complaints and any time that happens it's a plus."
Indeed, the special efforts of the project team did not go unnoticed by the public. In a letter to The Washington Post's "Dr. Gridlock" column, Robert Gerard of Bethesda, MD, went so far as to suggest that "before undertaking any major road repairs, all [State, local, and Federal] officials should spend a day with whoever was responsible for managing the repairs to the GW Parkway bridge. Those repairs were a model of how to repair roads with an absolute minimum of inconvenience to the public. Well done!"
What more could a project team ask for?
Gary Jakovich is a 1976 graduate of Renssaelaer Polytechnic Institute in Troy, NY, where he earned a bachelor's degree in civil engineering. He joined FHWA in 1978 as a trainee in the Highway Engineer Training Program. In 1979 he was assigned to the Bridge Design Office in EFLHD and has remained with that office since then. He is currently a design team leader. Over the years he has participated in the design and construction of numerous bridge projects, two notable ones being the Linn Cove Viaduct and the Arch Bridge over Tennessee Rte. 96.
Jorge Alvarez studied civil engineering at the University of La Paz in Bolivia, South America, and earned a degree in civil engineering at the University of Kentucky. He has done highway research for the Kentucky Department of Transportation research laboratory, highway investigation for the World Bank in South America, highway and metro design in the private sector, management and supervision as a vice president of an engineering company, and has served as project engineer for construction projects for EFLHD.