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Maine Demonstration Project: Reconstruction of Lamson and Boom Birch Bridges
MAINE HFL PROJECT DETAILS
The Maine HfL project included the reconstruction of the Lamson Bridge near Addison and the Boom Birch Bridge near Old Town (see figure 1). Both of these reconstruction projects involved full road closures of two-lane rural roads with relatively long designated detour routes. Among other aspects, this project demonstrates that the HfL program concepts do not apply only to large, complex bridge projects but also to smaller rural bridges. The majority of the bridges on the national inventory are short span rural bridges like these two Maine DOT bridges.
Lamson Bridge (Project No. BR-1264(000)X) carries Basin Road (State Aid Route 4), a rural minor collector, over Lamson Stream in the town of Addison, Washington County, Maine. The Lamson Bridge, built in the 1930s, was deemed as being structurally deficient due to substructure deterioration and a determination was made by Maine DOT to replace the bridge (see figure 2). The current annual average daily traffic (AADT) on the bridge is 680 vehicles, with 8 percent of those being heavy trucks, and a design hourly volume (DHV) of 95 vehicles.
A number of HfL innovations were adopted during the reconstruction of this bridge project which are discussed in the following paragraphs.
The Lamson Bridge is located in a narrow corridor with extremely poor sight distances and 1:1 side slopes necessitating a full road closure—a highlighted innovation for the project—for the majority of the construction time. The reconstruction project was further complicated by the proximity of bedrock near the roadway surface and location of the bridge in a marine environment. To construct a standard width bridge and approaches, retaining walls were required. The shortest available detour was about 16 miles from one end of the project to the other. Figures 3, 4, and 5 show the plan view, typical cross section, and elevation of the new Lamson Bridge.
At two town meetings, residents including commercial fishermen, the Town Selectman, and the Road Commissioner expressed concern about the duration of a full road closure and the associated impacts to the local economy. This site presents several construction challenges, including the installation of 120 linear feet of precast retaining wall that required a significant amount of excavation. The intention was to deliver a high-quality, long-lasting product that was completed in the minimum realistic timeframe. Keeping the road closure to a minimum was further aided by leaving the existing stone portion of the stream abutments (see figure 6) in place and keeping the construction of the new substructure in the dry, because no extra time was needed to construct cofferdams and to remove the abutments in this highly sensitive marine environment.
A typical timeframe for the removal and replacement of this type and size bridge is about 9 months using a cast-in-place substructure with footings founded on bedrock. Maine DOT's proposed structure incorporated a precast and precast/prestressed concrete system—a highlighted innovation for the project—that allowed a one-lane reopening after approximately 2 months and a full two-lane roadway opening only 3 months after the initial closure. After some consideration, this amount of time was chosen as a good compromise to accommodate the residents' concerns without significantly increasing the cost of construction. The scheduling of this road closure was also discussed at the formal public meeting. Maine DOT suggested starting the closure on June 15, 2007, to coincide with the public school summer break, but the residents requested a road closure date of July 15, 2007.
Early in the design process, the Maine DOT Environmental Office expressed concern that construction in this location could impact endangered species and would require a full Section 7 review. It was decided to increase the proposed bridge span and work behind the existing stream abutments. This took the new construction entirely out of the water, effectively made environmental concerns a non-issue, and removed the new bridge substructure from a corrosive marine environment.
The new Lamson Bridge included wider travel lanes and wider paved shoulders and raised the sag curve low point about 1 foot vertically. These improvements provided for safer vehicle travel and allowed pedestrians to cross the new bridge safely while cars passed in both directions. The DOT is also planning to set the speed limit in this location at 30 mph after completion of the project. It was not feasible to provide for higher speeds here which require significantly lowering the vertical grade due to the proximity of residential property adjacent to bridge and a rock ledge near each crest curve. Figures 7 and 8 show placing the abutment forms and the superstructure beams.
While precast/prestressed concrete bridge superstructures had been in common use for many years in Maine, the Lamson Bridge replacement project used a full system of prefabricated components. The combination of precast/prestressed and transversely post-tensioned beams and precast abutments had only been used twice in Maine, and they had not been used previously in conjunction with precast retaining walls that functioned as return wingwalls to the abutments. The use of a concrete voided slab superstructure where the precast/prestressed beams functioned as a single unit deck after transverse post-tensioning saved time and effort on deck construction, as illustrated in figure 9. As mentioned earlier, the use of such accelerated bridge construction methods was the central aspect of innovations used on this project and embody the core ideology of the HfL program.
Project work for the new bridge involved a full road closure and a 16-mile detouring of traffic, removal of the existing bridge superstructure and cast-in-place portion of the abutments, and construction of a new wider (28 feet curb-to-curb) bridge consisting of a 46-foot single span, precast/prestressed concrete superstructure with integral abutments. The superstructure included a 3-inch hot-mix asphalt (HMA) wearing surface with membrane waterproofing placed on a castin-place concrete leveling slab and a standard two-bar steel bridge rail, as shown in figure 10.
Also included were new full depth HMA approach roadways, guardrail, mechanically stabilized earth (MSE) retaining walls, riprap, grading, and drainage. Specifically, 200 feet of approach roadway, shoulder, and transitions (1000 square yards of pavement), 1320 square feet of modular precast concrete retaining walls, 350 feet of guardrail, 50 cubic yards of riprap, and two drainage structures with 60 feet of pipe were constructed or installed.
Due to the subsurface conditions, the precast abutments originally were designed to be supported by steel H-piles placed (not driven) in shafts drilled with a down-hole hammer and socketed into the underlying rock to achieve the necessary length and fixity. However, because of the relatively shallow rock and the decision to work behind the existing rock stream abutments, the contractor submitted a value engineering (VE) proposal to use cast-in-place spread footings instead of the H-piles. This proposal was accepted by the Maine DOT.
The prime contractor for the Lamson bridge replacement was CPM Constructors. The road was closed to traffic on July 15, 2007. Following the completion of the bridge (figure 11), and roadway reconstruction, the road was reopened on August 31, 2007, before the start of the school year. The total cost of construction was $912,000.00.
BOOM BIRCH BRIDGE
Boom Birch Bridge (Project No. BR-1266(100)X) carries the Southgate Road (State Highway 116), a rural minor collector, over Birch Stream in the town of Old Town, Penobscot County, Maine. Boom Birch Bridge was 69 years old, in structurally deficient condition, and in need of immediate replacement, as shown in figure 12. The Federal Highways Sufficiency Rating was only 21.8 out of 100. The deck was rated in "poor" condition and the substructure in "serious" condition. The AADT was 590 vehicles, with 8 percent of those being heavy trucks, and a DHV of 108 vehicles.
The environmental conditions, wetlands on one side and a river confluence on the other side, prohibited the use of an "on-site" detour on this project. Additionally, the age and severely deteriorated condition of the existing timber bent substructure precluded the use of phased (one lane at a time) construction. Consequently, it was determined to fully close the roadway and bridge to accelerate bridge removal and new bridge construction. This required maintaining a 14-mile detour on local roads. This closure decision and the long detour created much concern among local municipal officials, emergency responders, and the school district administrators. The Maine DOT met and worked with focus groups of these concerned stakeholders to achieve a workable solution. Figures 13 and 14 show the plan view and typical cross section of the new Boom Birch Bridge.
At two town meetings, residents and municipal officers expressed concerns about the duration of a full road closure, delays to fire and rescue response, commuting time increases, bus travel time, and the associated impacts to their local economy. The town manager expressed her support for the detour if the DOT could "fast track" the closure. Residents were greatly concerned that the bridge closure might extend into the school year. Setting a goal to open the new bridge in time to resume school-related traffic and a bus route on September 1, 2007, the closure was limited to 6.5 weeks.
The existing alignment was very straight and provided for adequate construction zone sight distance and safety. The proposed alignment was effectively the same, with the addition of a very slight crest curve over the bridge. The new alignment maintained the approach roadway profile at the existing elevations while increasing the elevation of the middle of the bridge by 1 foot. This allowed for improved deck drainage and added under-clearance for recreational boating under the bridge, as was requested by both boaters and residents.
The substructure of the existing Boom Birch Bridge consisted of timber bent piles and timber crib abutments. The timber ends at the top of the piers showed crushing and splintering from years of ice loads. The abutment cribs had evident scour. The deck had been extensively patched. The ongoing deck slab spalling caused a direct hazard to traffic. The bridge was rated structurally deficient, and substructure problems threatened potential failure in a relatively short number of years. Therefore, it was determined that a completely new bridge replacement was needed for safe traveling over the Birch Stream. The replacement bridge width, though only 26 feet curb to curb, was 5 to 6 feet wider than the previous superstructure.
The bridge inspector for this region flagged Boom Birch Bridge as a top priority due to its poor substructure condition rating. This warning remained effective throughout the programming process. This bridge replacement was fast-tracked through the programming and design phases as an accelerated construction project.
Project work consisted of a full road closure and rerouting traffic through a 14-mile detour, removal of the existing bridge, and construction of the new bridge. The new bridge consisted of three 47-foot prestressed concrete simple spans on precast, post-tensioned piers and abutments, as shown in figure 15. Plain elastomeric pads were used as bearings, and the wearing surface consisted of a 3-inch bituminous layer on a high-performance membrane waterproofing. The superstructure included cast-in-place concrete curbs and a standard two-bar steel bridge rail. The project also called for the construction of 210 feet of approach roadway, 500 cubic yards of heavy riprap blanket and side slope protection, 375 feet of guide rail, drainage features, and the re-grading of a gravel boat ramp within the project limits.
The Boom Birch Bridge was Maine's first bridge with precast post-tensioned pier caps, shown in figure 16. Pile driving for Boom Birch was no different from typical bents. However, the precast caps would save weeks of form construction, curing, and form stripping. Each of the three cap segments had a rectangular void to fit over the piles. Once each cap was placed and post-tensioned, the remaining void space was filled with a high-performance, fast-curing concrete.
All of the design was based on the American Association of Highway and Transportation Officials (AASHTO) load and resistance factor design (LRFD) code. Replacement in-kind, with steel beams, and precast deck panels was estimated, but proved to be not only considerably longer construction time, but also more expensive. The post-tensioned abutment caps and pier caps were designed by hand calculation. The pier pile group was designed by hand and checked with FB-Pier software. The simple span butted slabs were substantially designed with LEAP's CONSPAN software and checked by hand calculations.
This all pre-cast bridge was not only constructed rapidly, it was also relatively lightweight construction. The governing load criterion utilized 84 percent of the new pile bents' design capacity. Small load increases would have likely increased pier costs substantially by changing the required pier type from a pile bent to a wall pier. The pile cap for a wall pier would have to be placed at least 15 feet below streambed due to the highly scour susceptible soils at this site. Obviously, the deep cofferdam work would have had a large impact on the construction costs and schedule of this small project, not to mention the significantly greater impact on this environmentally sensitive area.
A typical timeframe for the removal and replacement of this bridge would have been about 9 months. Bents on piles, with cast-in-place caps would typically have been considered for both the abutments and piers. However, precast caps have never been used for pier bents in Maine before, and rarely for abutments. Boom Birch Bridge was the first multi-span bridge using precast post-tensioned pier and abutment caps. To further accelerate construction, cast-in-place concrete was eliminated from the bridge travel way (i.e., there was no cast-in-place concrete deck slab). All traffic was directly supported by the superstructure beam members, which were butted, precast/prestressed concrete voided slabs that were post-tensioned transversely. High-performance waterproofing membrane was placed on top of the butted slabs and doubled over the beam ends at the piers. All of these materials and designs promoted simple and rapid construction that is expected to have long-term durability.
As soon as the required concrete compressive strength was attained in the pier cap voids, the contractor placed the bearings (sheets of plain elastomer). Then the butted voided deck beams were erected and post-tensioned. Like the pier caps, the butted beams were prefabricated under controlled conditions in a manufacturing plant, figure 17. Temporary barriers allowed opening the bridge before the cast-in-place curbs were fully cured.
The 21-inch-deep beams were non-continuous, which means each simple span rotates independently under live load. At the piers between the beam ends, a ½-inch thickness of preformed expansion joint filler acts as a spacer, allowing the beam ends to rotate without harm to the superstructure. The caps for each abutment were precast in four segments, and the caps for each pier were precast in three segments. Transverse field post-tensioning held these segments together.
Another innovation on this project was the use of multiple pile anti-corrosion systems. Because of accelerated corrosion on exposed piles, the DOT has begun to install a two-coat system of hot-dipped galvanizing top-coated with an epoxy paint system. In addition to the double coating (one sacrificial and one barrier), a sacrificial zinc anode cathodic protection was installed at each piling. This new multiple protection system is expected to prolong the life of the substructure. The prime contractor for the Boom Birch bridge replacement was Wyman & Simpson. The environmental in-water work window did not start until July 15, 2007. This delayed the removal of the existing bridge, and consequently the beginning of the closure to the second half of summer. The road was closed to traffic on July 16, 2007. Following the completion of the bridge and roadway reconstruction, the road was reopened on September 1, 2007 (see figure 18).
Both the Lamson and Boom Birch Bridge replacements improved safety by eliminating the hazards associated with structurally and functionally deficient bridges. Additionally, the projects improved the alignment of the approach roadways and upgraded the traffic delineation and safety features.
Work zone safety for the motorists and workers was improved by using total road closures with concrete road barriers. The Maine DOT has a "zero work injury" policy.
The Maine DOT significantly reduced the traffic congestion caused by the replacement of the two bridges by using full road closures and prefabricated bridge elements. The desired result was to reduce the total construction time by approximately 80 percent.
Improve Quality and Durability
The quality and durability of both bridges were improved significantly by using bridge components prefabricated in a controlled environment, which provided a higher degree of quality control as compared to conventional cast-in-place construction method. This should result in a longer bridge component performance life with reduced maintenance needs. The use of high-performance concrete with specified higher strength precast/prestressed concrete (7.5 ksi compressive strength) reduced the structure's permeability to water and salts and will likely increase its durability. The durability of bridge travel surfaces was also likely improved and bridge maintenance costs and water damage potentially reduced through the use of integral abutments and waterproofing membranes under the HMA deck overlay. Maine DOT's cost-conscious customers were pleased and well served by getting a high-value product at the lowest long- term (life cycle) cost.
Improve User Satisfaction
The Maine DOT was fully committed to addressing the highway users, adjoining residents, local governments, and environmental needs and desires in the design and construction of both of these bridge/roadway replacement projects. The DOT satisfied all these concerns by totally replacing the structurally and functionally deficient structures with long-lasting, high-quality structures that were constructed very rapidly, as compared to conventional techniques. With this effort, Maine DOT continued to build public confidence in its effectiveness in providing safe and efficient transportation.
This page last modified on 04/04/11