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Rhode Island Demonstration Project: Replacement of Frenchtown Brook Bridge No. 435
Frenchtown Brook Bridge No. 435 carries Davisville Road, an urban minor arterial that starts at Frenchtown Road in the town of East Greenwich and proceeds generally in the southeasterly direction to U.S. Route 1 (Post Road) in North Kingston (shown in Figure 1). RIDOT included replacement of this bridge as part of its relocated Route 403 project, a major undertaking.
The16-ft-wide rectangular slab bridge built in 1955 at a 60-degree skew resembles a culvert (Figure 2). It was functionally obsolete and structurally deficient with a load rating of only 12 tons for a HS-20 vehicle. The concrete abutments that supported the structure had substandard dimensions. RIDOT decided to leave a portion of the existing substructure in place to minimize the impact on Frenchtown Brook, an important tributary of Hunt River.
Under the relocated Route 403 project, Davisville Road is no longer part of Route 403. The two one-way lanes and two shoulders to the north toward Frenchtown Road and the on-ramp to Route 4 North before relocation will serve as lanes for two-way traffic, a lane in each direction. With relocation, traffic volume of 10,200 vehicles per day (vpd) is estimated to drop to 7,300.
The traffic analysis in conjunction with the project indicated that it was feasible to detour traffic because the detour was short and the impacted traffic was primarily local.
RIDOT considered six alternatives to replace the structure, the first two of which appeared the most promising:
It was estimated that alternative 2 would cost $360,000 more if piling was needed and about $40,000 more if no piling was needed. Alternative 1 would not require piling because the loads on the footings would be much less because of the shorter span and more uniform bearing pressures.
RIDOT decided to go with option 1 and use precast elements for all segments of the structure for the first time in its project delivery history. This included both the footings and three-sided (roof and two legs) bridge segments for the main structure and precast elements for the footings and the wall stems for the four wingwalls of the bridge. See Figure 3 and Figure 4.
To complete the bridge construction work as quickly as possible and to lessen the impact of the project, RIDOT concluded that it would have to close Davisville Road to traffic. RIDOT further estimated that by using precast elements for all components, the closure period would be reduced from 6 to 2 months.
RIDOT applied for a HfL grant designed to advance longer-lasting highway infrastructure using innovations to accomplish fast construction of efficient and safe highways and bridges. A grant of $620,000 was made to RIDOT under the program.
Figure 1. Project location.
Figure 2. Old Frenchtown Brook Bridge.
Figure 3. Typical bridge section.
Figure 4. Conceptual typical wall element.
To ensure that the closure of Davisville Road would be for only a brief period, RIDOT included an incentive/disincentive clause in the contract specifications. For each calendar day that the bridge was fully open to traffic before the allowed 65-calendar day period, an incentive of $3,000 would be paid to the contractor. The incentive was capped at $90,000. A disincentive of $3,000 applied for each day the road was closed beyond the allowed 65-day period.
Other highlights relevant to precast concrete bridge elements included the following:
The contract was awarded to Aetna Bridge Co. of Pawtucket, RI, which had a low bid of $1.9 million. The contractor chose Contech Engineered Solutions of Palmer, MA, as its prefabricated elements subcontractor, located about 85 mi from the project site. The consultant designer on the project was Gordon R. Archibald, Inc. Professional Engineers of Pawtucket, RI.
The contractor started the roadway closure on July 30, 2012, for bridge construction. Approved shop drawings for the project are shown in the Appendix. The shop drawing package includes the bridge plan, foundation plan, upstream and downstream elevations, and a variety of connection details and specifications for manufacture and installation.
Construction of the project is highlighted in Figures Figure 5 through Figure 31.
The contractor started with dewatering measures, installation of demolition shield, demolition of wingwalls, and excavation behind the abutments. To minimize impact on Frenchtown Brook, a portion of the existing abutment was left in place (see Figures Figure 7 through Figure 9).
Figure 5. Bridge before closure.
Figure 6. Closure of Davisville Road.
Figure 7. Demolition of old structure in process with stream diversion in place.
Figure 8. Demolition showing slab removal with abutment walls left in place.
Figure 9. Abutment walls of old bridge left in place so work does not impact stream.
Figure 10 shows the plan view of the structure 150 ft long with 25 6-ft elements. The original plans called for concrete and grout subfooting under the precast foundation elements, but the contractor’s value engineering proposal to use a crushed stone subfooting wrapped in geotextile was approved instead. The precast foundation units were lifted off a tractor-trailer and placed on the subfooting. See Figure 11 for the construction detail and Figures Figure 12 through Figure 14 for the modular foundation element placement. The interior foundation elements are 23 ft, 11.5 in long, 6 ft wide and 2.5 ft high. The end units are of the same width and height and 26 ft, 11.75 in long. The units were hollow to facilitate transport and handling and were subsequently filled with concrete at the site. See the shop drawings in the Appendix for more details.
The three-sided 6-ft-wide bridge elements with an internal span of 28 ft shown in Figure 15 were lifted off the trucks and placed on the footings (see Figure 16). These elements came with a cable tie. The cables were removed after arch units had been erected and the concrete placed in the foundation units and at the arch unit had been allowed to cure to 2,000 psi. The headwall elements with their counterforts and wingwall elements with anchors were then placed. The butt joints between adjacent bridge elements were filled with preformed bituminous joint sealant and a 9-in-wide continuous joint wrap. A primer compatible with the joint wrap was applied for a minimum width of 9 in on each side of the joint. Other joints between the bridge elements and headwalls and bridge elements and wingwalls were similarly sealed (see Figures Figure 17 through Figure 25).
See the Appendix for grouting requirements at the joints. A minimum 28-day strength of 11,000 psi was required. The specifications for manufacture and installation also required that the lifting and erection anchor recesses be filled with grout.
Approved backfill shown in Figure 26 was rolled into place (Figure 27) and covered by a 5-in modified base course in two 2.5-in lifts followed by a 2-in bituminous surface course (Figure 28).
The road, which once served one-way traffic, was striped for two-way traffic (Figure 29) and opened on Friday, August 31, 2012, in time for the Labor Day weekend, just 33 days after it was closed to traffic. Figure 30 shows the completed structure with guardrail and riprap in place, and Figure 31 shows a view of the bridge opening with riprap placed behind old structure abutment walls.
Figure 10. Plan view of structure.
Figure 11. Bridge element support detail.
Figure 12. Precast foundation units being lifted off tractor-trailer.
Figure 13. Precast foundation unit being placed on subfooting.
Figure 14. Modular prefabricated footings in place.
Figure 15. Main bridge element with cable tie on flatbed.
Figure 16. Modular main bridge elements lowered into place.
Figure 17. All 25 main bridge elements lowered into place.
Figure 18. Modular headwall being lowered into place.
Figure 19. Wingwall support detail.
Figure 20. Modular wingwall being lowered into place.
Figure 21. Another wingwall being lowered into place.
Figure 22. Far end headwall being lowered into place.
Figure 23. Closeup of headwall anchors.
Figure 24. Closeup of wingwall anchors.
Figure 25. Prefabricated structure showing joints sealed and wrapped.
Figure 26. Stockpiled structure backfill.
Figure 27. Gravel backfill being rolled into place.
Figure 28. Bituminous material being rolled into place.
Figure 29. Davisville Road opened to traffic.
Figure 30. Completed structure with guardrail and riprap in place.
Figure 31. Bridge opening with riprap placed behind old structure abutment walls.