Bridges in the Era of Standardization, 1910s to 1950s
Eno River Bridge (Orange County Bridge 52) in Hillsborough, built by State Highway Commission in 1922 following state standards for reinforced concrete tee beam structures (Durwood Barbour Collection of North Carolina Postcards, UNC-Chapel Hill)
By the late 1910s, when North Carolina embarked on its statewide road and bridge improvement programs, the great period of innovation and experimentation in bridge designing was coming to an end. Two bridge-building materials—rolled-steel beams and reinforced concrete—had emerged as the prevailing materials based on their availability, economy, ease of erection, capacity, and maintenance requirements. The rolled-steel stringer and reinforced-concrete arch, tee beam, and slab types so dominated the national scene after World War I that bridges from North Carolina to Maine and California were virtually indistinguishable from one another.
Bridge department drafting room (Fourth Biennial Report of the State Highway Commission, 1921-1922)
North Carolina's historic highway bridges tend to reflect the national trends in bridge-building technology that were marked more by the increased strength and standardization of materials than development of innovative new bridge types. The state's bridges illustrate the nearly universal application of standardized types to any combination of crossing requirements. Standardized steel stringer and reinforced concrete, tee beam bridges accounted for more than 70 percent of North Carolina's pre-1961 highway bridges. The remaining bridges are a handful of other types, including metal truss; reinforced concrete arch, slab, rigid frame, and through girder; steel-girder-and-floorbeam; creosoted timber stringer; and movable bridges. In the mid-1950s, a new material, pre-stressed concrete, made its appearance in the state and was quickly recognized for its strength and versatility.