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Spencer Road Pedestrian Bridge. Montgomery County, Maryland.

The Montgomery County Department of Transportation needed to replace a pedestrian bridge to accommodate a Montgomery County Department of Permitting Services stream improvement project.

The MCDPS undertook a project to improve the Donnybrook Tributary to Rock Creek, located in Chevy Chase, Maryland, to reduce bank erosion which threatened loss of residents’ backyards. Between Donnybrook Drive and Farrell Drive, Spencer Road becomes a pedestrian path and bridge crossing. The existing bridge was a narrow paved path supported by steel roof-trusses on tall concrete abutments. Responsible for the bridge, MCDOT tasked WRA with the bridge replacement design. The chosen replacement bridge span length was twice as long the existing, significantly opening the waterway. To reduce future maintenance issues, WRA recommended a prestressed concrete New England extreme Tee (NEXT) beam bridge. The selection of this beam type allowed the contractor to construct the replacement by placing a single, stable beam without having to perform any cast-in-place construction over the stream, which expedited the task.

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Project Highlights

Geotechnical

With the project being located near Rock Creek, The visible rock in the project vicinity required an extensive subsurface exploration program with many rock cores being taken. In addition to providing exploration oversight, WRA’s geologists and geotechnical engineers analyzed the information obtained and provided recommendations for the structure foundations.

Water Resources

Hydraulic and scour analyses included predictive modeling of proposed conditions and well as recommendations for scour protection countermeasures.

Bridge

The length of the proposed bridge is approximately 64’-3”. Design expedited construction to the extent practicable by designing a single, stable beam with curbs cast at the shop and integral end diaphragms, which eliminated the need for backwalls and deck joints.