September/October 2002
The Bridges That Good Planning and Execution Rebuilt
by
Gary Jakovich and Jorge Alvarez
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.
![Photo of loop road before construction, pavement cracked Photo: All photographs courtesy of EFLHD Construction Office](images/02roadbefore.jpg) |
Condition
of loop road, before construction. |
All
photographs courtesy of EFLHD Construction Office
![Photo of loop road after construction, repaved and painted Photo: All photographs courtesy of EFLHD Construction Office](images/02roadafter.jpg)
|
Condition
of loop road, after construction. |
The
Challenge
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."
![Photo of Turkey Run Bridge before construction Photo: All photographs courtesy of EFLHD Construction Office](images/02turkeyrun.jpg) |
Turkey
Run Bridge before construction. |
![Photo of Turkey Run bridge after construction Photo: All photographs courtesy of EFLHD Construction Office](images/02turkeyrun2.jpg) |
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.
![Photo of old slab being lifted by crane Photo: All photographs courtesy of EFLHD Construction Office](images/02removedeck1.jpg) |
![Photo of slab being lifted Photo: All photographs courtesy of EFLHD Construction Office](images/02removedeck2.jpg) |
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.
Weekend
Work
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.
![Photo of new deck slab being lowered by a crane Photo: All photographs courtesy of EFLHD Construction Office](images/02newdeck.jpg) |
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.
![Photo of workmen placing latex-modified concrete overlay Photo: All photographs courtesy of EFLHD Construction Office](images/02placingl.jpg) |
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?