Atherton Bridge, Spanning Nashua River on Bolton Road, Lancaster, Worcester County, MA

Significance: The Atherton Bridge is an example of a hybrid pony-truss that bears a similarity to the Post truss. The bridge is 72 feet long, 18 1/2 feet wide, and is comprised of eight panels. It rests on granite abutments and was, at the time of its construction, the only iron bridge in Lancaster. Characteristics of the Post truss incorporated into the Atherton Bridge include compression members which incline towards the middle of the bridge, and tension rods which incline outwards. These tension rods and compression members extend over one panel except at the ends, where they extend over two. The compression members are formed of "Phoenix Columns," patented by the Phoenix Iron Company of Pennsylvania. The top chord consists of riveted compression members. The web members are joined to the top chord by pin connections while the web connections are joined to the bottom chord with screw connections. The bridge's wood and steel floor beams rest directly on the bottom chords of the truss. The floor beams support a wood plank deck. This structure retains an enormous amount of historical integrity. It is listed on the National Register of Historic Places. The Atherton Bridge is an unique variation on the metal truss designed by Simeon S. Post in the 1860s, and one of only a small number of Post-type bridges known to survive nationally. The Post truss enjoyed a brief period of popularity in the late 1860s and early 1970s and was used widely by railways for long-span river crossings. The Atherton Bridge is unique in that the web configuration resembles a Post truss, but the bridge does not incorporate Post's patented joints. The builders of the bridge, J.H. Cofrode & Company of Philadelphia, probably adapted the Post form for use in small highway bridges. The Atherton Bridge is locally significant as the first iron bridge erected in Lancaster. Although it has sustained structural damage from overloading, the bridge has not been significantly altered.
Unprocessed Field note material exists for this structure: FN-11
Survey number: HAER MA-17
Building/structure dates: 1870 Initial Construction
Building/structure dates: 1975 Subsequent Work