New Structure: Replaces Storm-Damaged Connecticut Bridge. (Statistical Data Included)
by Roger A. Krahn

12/01/2001
Public Works

Copyright 2001 Gale Group Inc. All rights reserved. COPYRIGHT 2001 Public Works Journal Corporation

The Blake Street Bridge. which crosses the West River in New Haven, Connecticut, was already in poor condition. There were settlement cracks along the vertical face of the east abutment stem and footing. The bridge also exhibited various degrees of scaling, and some hollow and deteriorated sections of concrete showed some signs of scour damage.

As early as 1995, the City of New Haven and the Connecticut Department of Transportation (CDOT) initiated a project to repair the bridge under CDOT's Federal Local Bridge Program. URS Corporation was retained to perform the engineering design. Work was expected to begin in 1996, but nature intervened and hastened the process.

On April 16, 1996, a storm categorized as a 50-year event, hit the New Haven area. Heavy rainfall raised the volume and speed of the West River. The resulting scouring! action undermined the eastern pier foundation, causing the bridge to give way. Due to the failure of the main pier support, the bridge was closed to traffic.

A DEPRESSION-ERA PROJECT
Ironically, it was another act of nature, 60 years earlier, that led to the construction of the existing bridge. Following a massive flood in 1936 and a hurricane that damaged many bridges in Connecticut two years later, the Blake Street Bridge was constructed in 1939. A creation of the Great Depression, it was federally funded as part of the Works Progress Administration, with work-relief agencies giving special attention to bridge replacement projects.

Though not technologically significant, the new bridge was more aesthetically pleasing than the mundane structure it replaced. It included art deco-style detailing such as stepped forms at the end of parapet railings and fluting on the outside of the parapets. It was a three-span, reinforced concrete T! -beam system, 95-ft long and 45-ft wide. Three 28-ft spans were supported on reinforced concrete abutments and piers. The overall bridge width carried two lanes of Blake Street traffic over a 30-ft roadway, with two six-ft sidewalks and 1.5-ft parapets on both sides.

The river channel was severely skewed at the north inlet side of the bridge and caused a heavy build-up of silt and vegetation at the west span. As a result, the center and east spans had been channeling most of the river's flow, and it was the east pier that failed. In 1990, as part of its flood-control project, the U.S. Army Corps of Engineers constructed several new features in the vicinity of the bridge, including an earth berm that would later be used as a temporary roadway during the reconstruction project.

The closing of the bridge created significant problems. The Blake Street corridor serves as an important transportation artery in the area, carrying more than 10,! 000 vehicles a day. With the bridge out of service, traffic patterns were adversely affected, causing disruption delays for emergency services in New Haven's Westville community. The extensive commercial development within the corridor made the reopening of the bridge critical to local businesses. New Haven Mayor John DeStefano, Jr., declared a bridge emergency on April 29, 1996, which set the replacement project on a fast-track course.

TWO-PHASE REPLACEMENT PROJECT
The city and state agreed to a two phase approach to remedy the problem.

Phase I consisted of the design and construction of a temporary bridge, including demolition of the existing structure, to be completed as soon as possible with emergency funding from CDOT. Phase II would follow with the design and construction of the permanent bridge. The Phase I project, which also included a temporary roadway approach, would restore traffic in a timely manner and allow the permanent! bridge to be constructed without impeding the flow of traffic.

The temporary bridge was a 101-ft, single-span Acrow Corporation of America (Carlstadt, NJ) panel structure. The structure, which had been used on previous projects, was disassembled in storage, and thus was quick and simple to construct. The project retrofitted the bridge to include a sidewalk on the north side, which allowed pedestrian movement to be maintained between the residential neighborhoods east of the bridge and the Westville section. Utility pipe hanger supports were used to buttress an eight-in, diameter water main and a natural gas main of the same dimensions.

Concrete abutments were designed to incorporate the required flood-control structure elevations established by the Army Corps of Engineers' flood-control project.

An unexpected construction obstacle was encountered when contaminated soil was discovered during excavation for the western abutments and roadway approach. To minimize interference with the Phase I construction schedule, as much contaminated soil as possible was left in place and the top layer was covered with geotextile fabric. All of the impacted contaminated soil was removed when the permanent bridge was put in place.

The temporary roadway approach east of the bridge was constructed on the earth dike that was part of the earlier flood-control project. The dike consisted of precast interlocking concrete block slope protection that was reconstructed as part of the temporary access roadway on the east approach.

The removal and replacement of the interlocking concrete blocks was accomplished mostly by hand.

MINIMIZING IMPACT ON BUSINESS
Great care was taken to maintain traffic flow to businesses on Blake Street during construction. Driveway entrances to a restaurant on the west approach and a manufacturing company on the east approach were kept open during construction of! both the temporary and permanent structures. Construction activity was staged to minimize its effect on a city park, and pedestrian access was provided along the temporary roadway adjacent to the park and across the northern side of the bridge. Water and gas lines were required to be reconstructed on both the temporary and permanent bridge structures. The temporary bridge and access roads were opened to traffic within three months of the start of construction.

The permanent bridge, which has been open for about a year, is 96 ft long and 45 ft wide. It carries two lanes of Blake Street traffic over a 30-ft roadway, with two six-ft sidewalks and 1.5-ft parapets on each side. The three-span structure was replaced with this single-span structure, eliminating piers in the water. The bridge superstructure is supported by prestressed deck units. All units are 3.3 ft deep, with eight units having a nominal 36-in, width and four units with a nomi! nal 48-in, width. A 12-in, water main is supported under the sidewalk on one side of the bridge, and 12-in, and six-in, natural gas pipelines are supported under the sidewalk on the other side. Pipelines are located in spaces between pre-stressed deck units, with channel supports welded to steel anchors set in pre-stressed deck units. Telephone conduit is located in the concrete sidewalk. The bridge parapet system consists of two square tubular metal bridge rails located between concrete posts.

A low-flow fish channel was created because the Connecticut Department of Environmental Protection and the National Marine Fisheries Service were concerned about interfering with the seasonal movement of migratory fish and the need to preserve fish spawning and nursery habitats in the West River.

Although construction of the permanent bridge was delayed more than a year due to lack of funding, the temporary structure kept traffic flowing and pro! vided ready access to businesses in the area. Total construction cost of the project was approximately $2 million.

Roger A. Krahn, P.E.
Mr. Krahn is a project manager for URS Corporation in Rocky Hill, Connecticut.