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I-85 Interchange Design-Build Project Using Prefabricated Bridge Elements in West Point, GA
The new I–85 interchange project in Troup County, GA, was selected as a recipient of a $1 million Highways for LIFE grant. The entire project covers the new interchange, a second bridge over Long Cane Creek, more than 10 mi (16 km) of four-lane frontage and access roadways, plus all the lighting, signals, and drainage improvements necessary to construct such a large–scale development. The overall project construction cost is about $81 million, of which the I–85 interchange is just over $4.3 million.
This entire infrastructure plan is in support of the new Kia Motors manufacturing plant and training center (the first Kia Motors plant in the United States) being built on a 2,200–acre (890–hectare) site along the west side of I–85, starting from north of State Route 18 and extending up to Gabbettville Road in Troup County. The site will generate thousands of daily auto and truck trips, most using I–85 to and from the site vicinity. This project is therefore critical to implementing safe, convenient, and efficient access to the area. The general project location and proposed interchange site are shown in figure 1.
The entire project was implemented under the D–B delivery method and the new I–85 interchange was built with innovative construction strategies centered on the use of prefabricated bridge substructure and superstructure elements. The interchange has a diamond-type configuration with four access ramps and a bridge that carries Kia Boulevard (formerly Gabbettville Road) over I–85. The bridge is a four– span concrete structure with eight columns per bent. Prefabricated elements make up the substructure's columns, pier caps, and deck beams. The elements were fabricated at the Hansen, Inc. casting facility in Pelham, AL. The contract was awarded to C.W. Matthews Contracting, Inc. and Arcadis D–B team. The following subsections highlight the innovative features of this project.
This was the State's first project using contract methods under the new Georgia law based on the GDOT State Transportation Board–adopted rule governing D–B procedures. The rule includes prequalification requirements, public advertisement procedures, scope of service requirements, letter of interest requirements, and request for proposal (RFP) requirements, which were used in determining a minimum of three and maximum of five qualified D–B firms. The D–B contract was awarded on a technical proposal and low–bid basis. This project reduced traditional construction scheduling from 30 months to 18 months through application of the D–B method with built–in contractor incentives and disincentives.
The D–B RFP special provisions included an innovative contracting approach requiring the D–B contractor to propose state–of–the–art methods to achieve specified performance goals, therein providing innovative recommended methods for monitoring and reporting various performance measures to achieve the HfL goals. Requiring the D–B contractor to propose these methods to achieve performance expectations is essentially performance–based contracting and a new approach for GDOT. This is a way of asking the industry to buy into the approach which gives them more flexibility to innovate.
GDOT required the contractor to define the performance measure methods as project deliverables tied to an incentive–disincentive approach, which is unique in Georgia. Execution is as enforceable as any other deliverable in the contract. Data reporting assessment will help determine the performance measures for GDOT's future construction contracts.
Several types of prefabricated elements helped make this project a success:2
2. "Prefabricated Bridge Elements" presentation, HfL Workshop, John Tiernan, Arcadis.
The focus of this subsection is the innovative prefabricated bridge substructure elements (PBSE) and how they were used to expedite construction, improve safety, and provide a high–quality finished bridge. The project plans incorporate prefabricated bridge columns and pier caps to construct the intermediate bents for the bridge. This is the first time PBSE were used in Georgia and is part of the strategy to incorporate innovation into the design.
The bridge components were cast offsite in a controlled environment and shipped to the site via conventional semitrailers. During fabrication a high level of care was taken to cast each component to within a 0.25–inch (in) (6.35–millimeter (mm)) tolerance so connections made in the field would fit precisely.
To take delivery, the contractor closed one lane of I–85 and offloaded up to four columns and pier caps at a time. Lane closure was kept to a minimum, normally for 1.5 hours or less, and occurred during nonpeak traffic hours, minimizing impact to the traveling public. The columns were temporarily stored onsite after delivery. Two columns per day were set early in the project, then, as experience grew, up to four columns a day were placed. Column placement is shown in figure 2.
Column footings (figure 3) were cast in place ahead of time with protruding reinforcing steel (12 bars per footing) that fit into a specialized coupler on the bottom of the columns. A bed of portland cement–based, nonshrink, high early strength grout was placed on the footing to receive the column, and additional specialized grout supplied by the manufacturer was hand pumped into the coupler's inlet holes. The coupler is designed as an emulation connection and in effect forms a nonthreaded butt splice between the longitudinal reinforcing steel in the column and the reinforcing steel in the footing.
Inside the coupler, the two ends of the rebars (about 12 in (304.8 mm) required for each rebar) come together and are surrounded by grout. The couplers are set in the column forms at the end of the main rebars during the precasting and embedded in concrete during the casting. The couplers have built–in tolerance of up to 0.5 in (12.7 mm) to accommodate rebar misalignment and to make field assembly between the substructure elements as quick and easy as possible. Figure 4 shows details of the coupler and figure 5 shows details of the column bar connection. Figure 6 provides details of typical intermediate bent construction and figure 7 shows details of a typical column.
Once the columns were set and checked for alignment with surveying equipment, the pier caps were placed on top of the columns in much the same way the columns were set on the foundations, except that the sockets in the pier cap had to simultaneously line up with reinforcing steel from two adjacent columns. At this point in assembling the elements, the 0.25–in (6.35–mm) tolerance became critical. Each intermediate bent has eight columns with four pier caps joining two columns each. Once the alignment was checked with the jig, the contractor was able to set one intermediate bent (four pier caps) in one day. Pier cap risers were cast in place to finish each intermediate bent (figure 9).
During construction, however, concerns about the schedule as well as how the segments would fit together led the contractor to propose a revised scheme. The revised scheme resulted in a defined detour route (see figure 6). The segments were replaced during three weekend full closures of the southbound lanes. As a result, rather than 12 separate single–lane closures on 12 nights, complete road closures on three weekends were used to replace the 12 superstructure segments, one span per weekend. VDOT's Public Affairs Office notified the public about the project and the traffic pattern during construction through news releases to the local media. Variable message system (VMS) boards were placed along the highway before construction to inform road users about the closure. The three full closures resulted in reduced risk because all four prefabricated segments were fitted together one span at a time. This change in the construction scheme also allowed the project to get back on schedule and be completed by the original completion date. A detailed discussion of the full closure traffic impacts is presented later in this report. Figure 7 shows the removal of one of the superstructure sections. Figure 8 shows the bridge superstructure partially replaced.
Similar connection was made between the top of the column and the pier cap. A steel jig was placed on top of the neighboring column as they were set to insure proper alignment (figure 8).
After the intermediate bents were assembled, 130 ft long prestressed "bulb–I" bridge beams were installed. Beam delivery required the contractor to briefly close both lanes in either the NB or SB direction of I–85. Up to three beams were removed from the transport trucks and set into place using two cranes while the lane closure was in place. Disruption to I–85 traffic flow was kept to a minimum by using short–duration lane closures to briefly offload the beams during times of low traffic volume (as revealed through real–time speed band monitoring). Preset dowels in the pier caps protruding through elastomeric bearing pads provided fast alignment of the beams. Setting each beam usually took about 10 to 15 minutes, after which I–85 traffic was allowed to resume. Figure 10 shows the beam installation.
The real–time speed band monitoring program supplied key information on traffic speed and volume, enabling the contractor to choose the most effective time to implement lane closures to take delivery of the bridge elements. This valuable information was also used to schedule lane closures for finishing the bridge deck and paving portions of the ramps connecting to I–85.
Real–Time Speed Band Monitoring
Real–time speed band monitoring was included as part of the D–B contract. It was the first time a contractor was required to provide this service to GDOT. The objectives of the system were to provide advanced real–time traffic information to the traveling public and to provide real–time speed and volume data for evaluation.3
Traffic volume through the work zone was closely monitored with the system. Decisions on the times of the day and week best for lane closure were based on this information. This real–time input led to changes in the original lane closure plan from traditional nonpeak hours in the evenings, nights, and weekends to a new schedule of 8 p.m. Sunday and through Tuesday evening. The contractor noted an increase in traffic volume during community activities on Sunday, which prompted rescheduling of the lane closures to later in the evening to ensure less disruption to work zone traffic.
3. HfL showcase presentation, Dr. Prahlad Pant, PDP Associates.
Major components of the system include the folloring:4
The system was able to successfully provide the following:3
The access ramp shoulders of the new interchange were paved with RCC. The finished color of the RCC is slightly different from the portland cement concrete (PCC) ramp travel lane, enhancing delineation and increasing roadway safety.
Using RCC was good for quick installation of the shoulders and was demonstrated on this project to be a timesaver. However, a smooth surface profile was difficult to obtain with RCC. As constructed, it was suitable for shoulder–type work, but not necessarily for high–speed traffic lanes.
This page last modified on 04/04/11