Chain Bridge

Structure Description

Structure Type:

Single-span, steel wire cable suspension bridge with 2 pairs of cables. Each cable is 3 1/2" in diameter, and contains 210 individual wires, each 0.192" in diameter, laid parallel. Each cable is wrapped with a 0.135' diameter soft iron wire. Suspenders are 1 1/4" steel wire cables, looped through hanger assemblies at the ends of each floorbeam. The slightly bowed deck is stiffened by steel, single-intersection Warren pony trusses which are hinged at their pier ends and at the centerline of the bridge. Reinforced concrete towers on earlier stone masonry piers carry cast saddles on 8-roller nests. The main cable ends are linked to groups of 1" x 5' steel eyebars in massive concrete anchorages.

The original timber deck was replaced in 1922 and 1931; all timber stringers and deck planks were removed 1938 and replaced with an Irving open steel grid deck on steel stringers. All hinges of both stiffening trusses rebuilt in 1935.

History of Bridge:

The first bridge on this site was a Palladian, arched timber truss designed and built by Timothy Palmer in 1792. This was replaced in 1810 by a wrought iron chain suspension bridge designed by James Finley and constructed by John Templeman. On Feb. 6, 1827, the bridge gave way under a heavily loaded ox cart, and was rebuilt (again using wrought iron chains) in the summer of 1827. Sometime before this 1827 bridge was removed in 1909, a pair of cables and a pair of timber stiffening trusses had been added to the eastern barrel of the bridge--this was almost certainly done when the local street railway line was allowed to run its line over the bridge in 1894.

By the early 20th century, the 1827 Chain Bridge had been deemed unsafe and, in 1908, it was turned over to the Essex County Commissioners who immediately started plans to rebuild it. Local attachment to the 1827 landmark was so strong that the county's initial plans were for a new steel cable/steel tower suspension bridge disguised by shingled tower sheathing and by rehanging the 1827 iron chairs (although in a non-structural capacity). These preservationist features were dropped, however, as the local clamor died down. The present bridge, with its reinforced concrete towers (which echo the shapes of their timber predecessors), and its undisguised steel wire cables, was erected in 1909.

Significance of Bridge

The only known suspension bridge in the MassHighway database, and one of only two known suspension bridges remaining in the state (the other being the 1866 eyebar chain suspension bridge in Boston's Public Garden, which no longer functions structurally as a suspension bridge, as a result of an early 20th century remodeling). Little altered and visually arresting. It is located on the site of two earlier bridges which were of national significance.

Within the development of the suspension bridge structural type, this is an essentially "modern" design in that it uses steel wire cables (rather than link or eyebar chains), has a nearly horizontal deck, center-hinged stiffening trusses, and no stay cables.

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