User:KevinButler22/sandbox

Tyngsborough, MA is probably best known today for its green painted single-arched iron bridge over the Merrimack. This bridge has become the town’s emblem and more practically, a major river crossing for residents of Massachusetts and New Hampshire alike. The Tyngsboro Bridge is located in Tyngsboro, Massachusetts, and the Massachusetts Highway department owns the bridge, as well as route 113 which runs over it's 656′ span. Although officially called the Tyngsboro Bridge, some, especially young children of the area refer to the structure as the "Big Green Bridge."

Structure
The Tyngsboro Bridge is 656′ long and 41.5′ across. Erected as 3-hinged steel trussed rib through arch; center hinge fixed upon completion. Arch ribs are 20′ deep tapered in end panels to a point at end hinges. Pratt-type trussing in the arch ribs with 34 panels. The 2 crown panels have crossed diagonals and heavy horizontal struts, which are pinned at the centerline. Upon completion of the bridge and with all dead load in place, the crown hinge was fixed by means of riveted plate connections between the opposing ends of the upper and lower chords. Pinned steel I hangers carry the strongly cambered deck. Deep portal frames; heavy upper lateral system, with sway bracing at panel points.

History
Boston Bridge works originally built the Tyngsboro Bridge in 1930, and from 2004 to 2012 the bridge was closed for repairs, a new roadway and a new paint job. The Tyngsboro bridge replaced a 4-span iron whipple truss bridge built 1873, which in turn replaced fairy services across the river. The bridge is the 2nd oldest of 5 positively identified steel rib through arch bridges in the MassHighway database, and one of only 13 known steel rib arch bridges of any configuration in the database. One of only 2 of the 13 to utilize an open, braced rib design (the Boston University Bridge, Boston is the other). The Tyngsborough Bridge’s 547 foot main span is the longest simple steel arch span in the MassHighway database, and the 5th-longest single span amongst all bridges listed in the database.