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Bridgetown Pike Bridge Replacement Project ASHE Nominee-2001 Project of the Year
By Peter W. Berthold, P.E., Pennsylvania Department of Transportation

When the Pennsylvania Department of Transportation decided to replace the existing bridge with a new bridge on new alignment outside the floodplain, the Bridgetown Historic District (which is comprised of four historic properties bordering the project) required that the "crossroads" between Bridgetown Pike and Newtown Pike (S.R. 413) remain within the same alignment. The relocation of Bridgetown Pike to the new alignment would have resulted in the elimination of the "crossroads" of Bridgetown Pike and Newtown Pike and the demolition of the stone mill floodgate walls, headrace walls, and a portion of the headrace. Consequently, SITE-Blauvelt Engineers was retained by PENNDOT Engineering District 6-0 to provide consulting services that were needed to replace the structure, maintain the cultural features of the historical district, and improve safety and traffic operations within the study area.

The Bridgetown Pike (S.R. 2010) Bridge over Neshaminy Creek was borne out of the need to replace an existing two-span, 142-foot-long, riveted-steel, pony-truss bridge over the Neshaminy Creek. The existing structure (which was ultimately left in place) provided a total cartway of only 14-feet by 8½-inches and was rated for a maximum load of three tons. In addition to the substandard load rating, the existing bridge had many design deficiencies that resulted in the need for its replacement. First, the structure provided insufficient width to allow two-way vehicular traffic. Second, the bridge was located within a flood plain at the confluence of Core Creek and Neshaminy Creek that not only resulted in flooding of the structure and approach roadways during a 50-year storm, but also contributed to excessive scour at the pier and abutments. Finally, the roadway alignment did not provide the needed sight distance for motorists to see oncoming traffic before crossing the bridge, thus resulting in traffic delays and safety concerns.

The result was the design and construction of a new structure to carry Bridgetown Pike over the Neshaminy Creek, in addition to an additional structure replacement on Newtown Pike (over Core Creek), realignment of the intersection of S.R. 2010 and S.R. 413, various roadway safety improvements, implementation of a bicycle/pedestrian facility, and enhanced bicycle and pedestrian facilities.

Significant Design Issues
The existing bridge was structurally unsafe and badly in need of repairs but was to remain in place during and after construction. In addition, it was necessary to eliminate an existing substandard "S" curve in the alignment of S.R. 2010 (west of its intersection with S.R. 413) that would greatly improve the operation and safety of S.R. 2010. Realigning the intersection of S.R. 2010 and S.R. 413 also was necessary to rectify safety and capacity deficiencies caused by the offset of two legs of S.R. 2010 and to raise S.R. 2010 above the 50-year flood levels without increasing backwater.

To arrive at the most viable solution and avoid the use of properties that were protected under Section 4(f), six alternatives were considered that underwent extensive study. After careful evaluation and coordination between PENNDOT and the project stakeholders, the recommended alternative was to build a new structure adjacent to the existing structure and maintain the crossroads. The existing structure would be used as part of a pedestrian/bicycle facility running thru the project from Core Creek Park. The proposed action was selected because it would minimize the impact on the Historic District, require minimum right-of-way acquisition, and rectify the roadway, traffic, and structural deficiencies that were present.

Data from previous FEMA studies indicated that both Neshaminy Creek and Core Creek could cause flooding. As S.R. 2010 is relatively level in this area, the opening of the structure had to be increased to maintain the current channel flow rates and backwater. An H&H study indicated that a 290-foot, continuous two-span steel girder structure would pass 100-year flood levels. Furthermore, significant attention had to be paid to the design and alignment of the pier to reduce scour.

To properly assess the potential for future scour and determine the appropriate foundation type, a comprehensive geotechnical study was completed that established the need for a pile foundation system that had the potential to resist high-stream velocities and provide stability for a 42-foot high abutment on the eastern leg. Alternate low-strength backfill was provided to allow the contractor the opportunity to provide the most economical foundation system.

Because the existing bridge had been observed to be in flood conditions and has always been at risk of washing out, design provisions were made on the new crossing for an 8-foot pedestrian and bicycle lane in the event that the steel-pony truss became damaged. Furthermore, the substructure provides for the future addition of a travel or turning lane if traffic at the intersection of S.R. 2010/S.R. 413 increases above the 20 year study area and requires additional roadway capacity in the future. Such an addition is made possible through the provision of an extended pedestal and footing width at the pier.

Description of Contract
The project bids were opened in March 2000, with Loftus Construction being awarded the contract. The contract provided for 24-months to complete demolition and construction of the entire project. This included the Neshaminy Creek crossing, intersection improvements at S.R. 413/S.R. 2010, intersection improvements along the detour route, bicycle and pedestrian path, and replacement of an adjacent bridge along the detour route, bicycle and pedestrian path, and replacement of an adjacent bridge along Newtown Pike crossing Core Creek that was impacted by the improvements to the intersection.

The proximity of emergency services that traveled the structure and the current traffic volumes along Bridgetown Pike, caused a review of the six-month closure proposed for the bridge during construction. This closure was reduced to two weeks by constructing a temporary roadway on an adjacent property owner's frontage, constructing a temporary pile and lagging retaining wall to withstand embankment needed to construct the new structure, and installing a one-lane narrow roadway, with temporary traffic signals on each end controlling the direction and flow of traffic. Secondary impacts were identified along the detour route and were mitigated through the implementation of intersection and signal timing improvements.

The estimated cost for the project was $6 million. Through the aggressive maintenance and protection of traffic program, project work task scheduling, and innovative construction solutions to problems experienced in the field, the project was completed in only 18 months, with a final cost ($5.4 million) that was 90% of the estimated amount.

Significant Techniques
The new structure on Bridgetown Pike is a two-span, continuous-composite, steel-plate girder, with one span being 148-feet long and the other 142-feet long, supported by concrete abutments and a pier with steel H-pile footings. Weathering steel was used for the superstructure, steel beam guide rail, posts, terminal section, and all appurtenances and hardware so that it would blend with the historical surroundings.

On the western leg of Bridgetown Pike, a mechanically stabilized earth (MSE) retaining wall was constructed to protect the recreational/bike trail from motorized traffic and to retain the embankment of the proposed roadway. The wall was connected continuously with the proposed bridge structure, and the same aesthetic treatments were used to maintain the rustic appearance of the structure.

To match the colors and textures of the site, SITE-Blauvelt focused on the colors and textures of the native building materials. To blend with colors found in the immediate vicinity of the site, the concrete was stained and mortar joints were used to simulate the look of laid stone. The form liners that were used for the concrete provided a random looking pattern of stone. By staining the concrete at individual stones, additional variation was provided to give a natural look.

Landscaping around the bridge was important because of the historic setting of the area. Every effort was made to limit the necessary work zone utilized by the contractor and reduce the number of trees that were required to be removed. Areas that had to be disturbed were regraded and planted with tree species that were agreeable to the adjacent property owners and the Historical District Society.

Although the footers were supported on piles, the pile caps had to be depressed below grade to minimize the potential for future scout. This required the contractor to install a temporary cofferdam to divert Neshaminy Creek around each substructure being constructed and divert Core Creek through temporary pipes around the back of the abutment to also minimize its impact. Because of unexpected storms through the first construction season, the contractor had to reestablish the stream diversion and temporary stream crossing during construction of the pier and abutments.

Because of the height of the abutments (42 feet), high-strength concrete was used along with low-specific gravity backfill material. The causeway was reinforced with additional strength to provide for the 900-ton crane that was needed to aid the contractor during beam erection. With the 148-foot spans and use of the larger crane, the beams were off- loaded on one end of the bridge and swung into position.

Positive community relations were key to the successful completion of the bridge replacement. The design was developed in conjunction with the steering committee and the Historical District Society, which emphasized the need to maintain the historical crossroads and build the structure within a flood plain. Various historical and aesthetic issues arose during construction, as well as the concern that the new bridge would contribute to increased flooding problems. To the satisfaction of the community, the contractor was able to reestablish Core Creek to an improved condition with the completion of the new structure.

 






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