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South Carolina Demonstration Project: Black River Bridge Replacements on SC 377 in Williamsburg County
This project is located about 4 mi south of Kingstree in Williamsburg County, SC. The project consisted of replacing four reinforced concrete bridges and realigning and improving the intersection of U.S. 521 and SC 377. The four bridges include the main bridge over the Black River and three overflow bridges over adjacent swamps. The bridges, about 52 years old, were found to be structurally deficient. Figure 1 is a map showing the general location of the project. Figure 2 is a schematic of the project.
Figure 1. South Carolina HfL project location.
Figure 2. Schematic of project layout.
The 2006 annual average daily traffic (AADT) for the four highway sections in the project area was as follows:
Commercial vehicles comprised 6 percent of the AADT. Table 1 lists details of the four bridges that were replaced and table 2 lists details of the highway and intersection improvement work.
The Black River bridges carry SC 377, a two-lane rural highway, over the Black River and adjacent wetlands near the town of Kingstree in Williamsburg County, SC. The bridges were built in 1955 with reinforced concrete and a substructure consisting predominantly of steel piles. Over the years, significant deterioration and corrosion of the steel piles was noticed. SCDOT survey results indicated the main bridge over the river was structurally deficient (with a sufficiency rating of 10.8 on a scale of 0 to 100). In September 2003, this bridge was posted for a load restriction for trucks of 3 tons per axle or 5 tons gross weight.
The surrounding community is rural and a majority of the truck traffic using this route carries agricultural goods and timber. After the bridge was posted for load restrictions, truck traffic was switched to a detour (figure 3) of about 14 mi. Passenger vehicles also were detoured for 5 days to allow the contractor use of the full roadway. Figures 4 and 5 show the original Black River Bridge.
Figure 3. Detour route.
Figure 4. Original Black River Bridge.
Figure 5. Black River Bridge pile detail.
The original bridge deck structure consisted of about 10 inches of reinforced concrete and was supported by steel beams. The steel beams rested on concrete pier caps supported by steel piers. About 0.5 mi from the main bridge is the intersection of U.S. 521 and SC 377. Reconstruction of this intersection included safety enhancements and geometric modification, such as additional widening and turn lanes to ensure smoother and safer traffic flow. Figure 6 shows the original intersection of U.S. 521 and SC 377, looking east on U.S. 521. Traffic at this intersection was controlled by stop signs and warning signals on SC 377.
Figure 6. Intersection of U.S. 521 and SC 377 before reconstruction.
Since this route is used frequently by local residents, a full closure of SC 377 to facilitate bridge replacement work would have included a long detour for all vehicles. An option would have been to build the new bridges next to the existing bridges. However, this option would have significantly impacted sensitive wetlands areas and increased the amount of roadwork involved in the project. Therefore, SCDOT decided to adopt a two-phase construction approach, which minimized the environmental footprint of the new bridges and kept lane closures to a minimum.
The HfL innovations adopted during the reconstruction of this project include the following:
Road Safety Audit
Transportation experts from the SCDOT conducted a road safety audit (RSA) prior to construction to ensure that all aspects of safe operation of this roadway were noted and recorded to enable appropriate decisions on resource allocation. The RSA team noted that U.S. 521 is a designated evacuation route. While the team believed that the project would not have any major impact on the functionality of U.S. 521, the possibility of such an event should be considered. Since the staged work on U.S. 521 was vital to the staging of the rest of the project, an active hurricane season could possibly hamper the staging, thus delaying the project. Conversely, the team noted that if an evacuation was ordered, the project’s possible impact on traffic flow should be considered. In addition to traffic flow concerns, the RSA team made the following safety recommendations:
Given that time was of the essence in restoring truck traffic, SCDOT developed a project-specific A+B+C bidding provision to encourage the contractor to strive for efficient production methods and achieve the shortest possible construction time. The provision had the following components:
Table 3 shows the results of the bidding process.
Although the winning bid was $1.5 million more than the second bid, 270 days were saved on the final product. Of the total, 125 days were saved on phase 1 of the project. This project was awarded to the winning bidder, United Construction Inc. The total project cost, discussed in the "Economic Analysis" section of this report, takes into account the cost of the B and C portions of the contract plus incentives awarded to the contractor for early completion.
This type of a bidding process enabled the contractor to determine the time necessary to complete the project according to the contractor’s capabilities. The project was bid with a shortened timeframe, which allowed for a more competitive bid price. With an accelerated timeframe to complete the project, contractor crews worked 7 days per week instead of 5. This was made possible by the availability of multiple crews and crew rotation. The incentive portion of the bid helped offset some of the costs of overtime pay. A drawback of this accelerated schedule was that materials and deliveries were not always available on weekends, plus construction crews and SCDOT inspectors had to work on weekends. In addition, SCDOT engineers use a 5-day calendar when making approvals and decisions.
This special provision was included in the bid to attract bids with the shortest possible construction timeframe. According to this provision, the bonus or incentive was paid to the contractor only if the project was substantially completed before the deadline. This could not be adjusted for any reason except a catastrophic event. The no-excuse bonus was $9,000 for each day the contractor finished interim construction ahead of schedule. The bonus was restricted to 30 days ($270,000). By offering this bonus, the contractor was encouraged to complete the project ahead of schedule, reducing the duration of the truck detour.
SCDOT developed a new ride quality specification with incentives. On this project, the maximum acceptable IRI for each nominal 0.1-mi segment of vehicle lane, when tested in accordance with SC-T-125, is 65 inches per mile. When initial measurements are 65 inches per mile or less, payment is based on the original contract unit price per ton of final hot-mix asphalt (HMA) surface tested, shown in table 4. The pay adjustments summarized in table 4 apply only to the surface course of HMA. The surface course was not as smooth as SCDOT required, and the contractor has milled and replaced several areas at its own expense.
SCC is an innovative concrete product that has excellent deformability and resistance to segregation. It can be placed in heavily reinforced formwork without difficulty and can result in high-quality smooth surfaces. This project included the use of SCC in bridge beams for the first time in South Carolina. SCDOT, with the help of the fabricator and USC, developed an SCC mix and special provisions for its use in casting the bridge beams.
Since SCC is significantly more fluid than normal concrete and is more resistant to segregation, the concrete can flow more easily in a heavily reinforced structural cross-section. This fluidity reduces the potential for honeycombing in concrete. SCC proponents claim that the main advantage is a substantial reduction in labor hours and total production costs by using fewer workers to pour, vibrate, and finish the structural elements. According to Martin (2002)1, the increase in material costs for SCC is about 17 percent, which can easily be offset by improvements in pouring productivity (about 47 percent) and reduction in vibrator and
1 Martin, D.J. Conference Proceedings: First North American Conference on the Design and Use of Self-Consolidating Concrete, November 12-13, 2002.
equipment maintenance costs. SCC also has a safety advantage because workers are not on top of the casting forms carrying vibrators and power cords, which are a tripping hazard during fabrication. The result is high-quality beams that should last longer than conventional cast beams and are fabricated with fewer workers.
Staged Construction—Phase 1
The prime contractor for this project was United Construction Inc. Several subcontractors were retained, including Goodson Construction and C&R Asphalt for the roadwork portion of the project. Phase 1 of the project consisted of constructing two-thirds of the width of the new bridges next to the existing bridges. The existing bridges were 26 ft wide, whereas the new bridges were 44 ft wide (two 12-ft-wide traffic lanes and 10-ft shoulders). Figure 7 shows a schematic of phase 1 construction of the main bridge. Figure 8 shows the profile and elevation of the main bridge.
Construction preparation began in late October 2007. The initial construction period for phase I was planned at 210 days. Light vehicle traffic was maintained on the existing bridges while construction was started. All truck traffic was maintained on the detour route during phase I.
Figure 7. Phase 1 construction details.
Note: Span 3 (shaded) has SCC beams.
Bridge Beams Manufactured with Self-Consolidating Concrete
As mentioned earlier, this project included the first use of SCC bridge beams in South Carolina. SCDOT had a research contract with USC to develop SCC mixes and full-scale testing. The main objectives of this research were as follows:
USC performed full-scale testing on similar SCC and high-early-strength concrete beams in May 2006. Researchers found that comparable crack patterns and failure modes were obtained in both types of concrete beams under load testing. They concluded that SCC beams were a viable alternative to conventionally poured heavily reinforced concrete girders. A demonstration bridge project was planned to evaluate the feasibility of SCC beams in bridge construction.
The SC 377 project was chosen as the demonstration project for the use of SCC beams. The beams, prestressed AASHTO Type III bridge beams, were fabricated by Standard Concrete Products Inc. of Savannah, GA, in March and April 2008. Figures 9 and 10 show the fabrication process.
Figure 9. Fabrication of SCC beams.
Figure 10. SCC beam pretension tendon detail.
Six SCC beams were fabricated for this project. As part of the research effort, four SCC beams were instrumented with strain gauges. USC has a contract to monitor the performance of SCC and conventional beams used in the project. Researchers installed the strain gauges and lead wires before SCC was poured into the forms (figure 11). On each instrumented SCC beam, two vibrating wire gauges were placed at the top and bottom of the beam at mid length. Temperature gauges were also installed.
Figure 11. Strain gauge installation in SCC beams.
During fabrication, researchers measured the properties of fresh SCC. These tests included the SCC spread test, U-box test, L-box test, and air content (pressure method) test. The researchers cast several compressive strength test cylinders for further laboratory tests.
Construction of the Black River Bridge
After fabrication in Savannah, GA, the SCC and conventional beams were transported to the construction site by trucks. Construction of the Black River Bridge substructure began in April 2008. After the beams were set (figure 12), the contractor placed the formwork and plates for the bridge deck. The bridge deck concrete was poured on May 14. Figure 13 shows the completed phase I of the bridge.
Figure 12. Construction of Black River Bridge (Phase I).
Figure 13. Black River Bridge after phase I of construction.
The contractor completed construction of phase 1 30 days before the deadline and collected the full bonus ($9,000 x 30 days = $270,000). Construction on adjoining earthwork and roadwork between the four bridges was also in progress during this time.
For only 5 days, the road was closed through the work zone and all traffic was diverted to the detour route. This closure was necessary to tie in the adjacent roadwork to the new bridges. On June 12, 2008, the new phase I portion of the bridges and connecting highway pavement was reopened to all traffic, including trucks, and phase II of construction began.
Staged Construction—Phase II
Major construction activities during phase II include the following:
Figure 14 shows the construction details in phase II. As seen in the figure, the shaded portion represents phase II construction of the new bridge (one-third width). The old bridge was demolished before construction commenced on phase II.
Figure 14. Phase II construction details.
Figure 15 shows the demolition of the main bridge. After all of the old bridges were demolished, construction was started on phase II. The initial project completion date was February 2009 with conventional construction methods, but the accelerated schedule accepted by SCDOT and the contractor called for a December 2008 completion date. As noted earlier, construction on this accelerated schedule was made possible by employing extra crews and working 7 days a week.
Figure 15. Demolition of the old Black River Bridge.
The bridges were ready for deck concrete placement in late September 2008. Bridge deck concrete was placed within the span of 1 week on all four bridges. Figure 16 shows phase II of construction. Figure 17 shows a typical completed section of the bridge.
Figure 16. Phase II of construction.
Figure 17. Completed typical section of the main Black River Bridge.
The asphalt surface course was placed late November 2008. However, because of problems stemming from paving late in the season, the final surface was too rough to be accepted under the performance criteria in the contract. Traffic operated on the highway throughout the winter, and the surface was milled and repaved in spring 2009. SCDOT accepted the final surface course.