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Irwin Viaduct

Irwin Viaduct

Primary Photographer(s): Nathan Holth

Bridge Documented: June 3, 2012

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Key Facts

Facility Carried / Feature Intersected
US-30 Over Tinkers Run and Main Street
Irwin: Westmoreland County, Pennsylvania: United States
Construction Date and Builder / Engineer
1939 By Builder/Contractor: Unknown and Engineer/Design: Pennsylvania State Highway Department

Technical Facts

Rehabilitation Date
Main Span Length
75 Feet (22.9 Meters)
Structure Length
524 Feet (159.7 Meters)
Roadway Width
50 Feet (15.24 Meters)
8 Main Span(s)
NBI Number

Historic Significance Rating (HSR)
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Bridge Documentation

View Archived National Bridge Inventory Report - Has Additional Details and Evaluation

This bridge is a high level steel stringer bridge that carries US-30. It contains continuous spans, an early use of continuous stringer design by the state highway department. The bridge is unusual because it has steel bents for supports and these bents are significant because they use rolled H section. This was an early use of these types of rolled beams in bridge design in Pennsylvania. The deck of the bridge has been replaced as have the original railings. In contrast, the superstructure and substructure appears to be largely unaltered.

Information and Findings From Pennsylvania's Historic Bridge Inventory

Discussion of Bridge

The 524' long and 52' wide, 8 span viaduct is composed of from west to east 3 span continuous steel stringer spans (1 @ 60'-6", 1 @ 64'-6", and 1 @ 76'), a 29' long stringer span, and 3 span continuous steel stringer spans (1 @ 86'-6", 1 @ 74', 1 @ 67'-6"). It is supported on concrete abutments and bents with H-pile columns and built up cap beams. The safety shape barriers and present concrete deck were placed in 1984. The bridge is historically and technologically significant as an early example of both continuous stringer technology and the use of rolled H section in a substructure.

Discussion of Surrounding Area

The viaduct carries a 4 lane highway with shoulders over a stream, a county road, and a township maintenance yard near an area of 20th century residences in Irwin. The bridge does not appear to be part of a potential historic district as it is a large, overhead structure. This section of US 30 was built in the late 1930s as part of a bypass around Irwin. PHMC has a Multiple Property Documentation Form for resources associated with the Lincoln Highway/US 30 corridor from Franklin through Westmoreland counties. The period of significance is 1750-1947. The alignments of the Lincoln Highway are not considered a historic resource or historic district.

Bridge Considered Historic By Survey: Yes


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Maps and Links: Irwin Viaduct

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