Bridge C601 Elm Street over the South Branch of the Raritan River
This is a two span lenticular truss bridge constructed in 1896 by the Berlin Iron Bridge Company of East Berlin, Connecticut, using a design patented by William O. Douglas in April, 1885. Each span is 140' 7'' long. The bridge gets its name from the appearance of the top and bottom chords; the top is curved downward and the bottom curved upward, making it look like a lens. (The patent refers to it as a parabolic truss.) This bridge is the only functioning lenticular truss in New Jersey.
The top chord is made of two vertical C channels with a plate riveted across the top. It originally had a plate closing the bottom, but this was removed as part of the strengthening done in 1984. The bottom chord is composed of flat eye bars. The vertical struts are L channels with lacing bars riveted to them. Round web ties and various types of bracing keep the structure rigid.
Because the bridge was unstable in the lateral direction, i.e. it tended to move along its center axis, additional stiffening was added in 1932 by bracing the end portals at all four ends. This addition is maintained in the current rehabilitation. In 1984 the bridge was further strengthened by bolting steel I beams inside the top chord channels. Continued deterioration lowered the load rating to three tons.
The bridge was dismantled by inserting an Acrow truss through it and using this as a support to which the bridge was attached at its verticals. It was then possible to remove it without any danger of collapse. It was reassembled by reversing the process; the verticals were first attached to the Acrow and the other components added.
Upon inspection of the disassembled bridge, it was discovered that the verticals were too deteriorated to be reused, so new ones were fabricated. All the parts, both old and new were galvanized and painted. The bottom chord was strengthened by the addition of U-bolt and rod connections between the nodes. An additional brace was added from the bottom of each end post to the first lower node. It is not known why this strut was not on the original bridge, as it is shown on the 1885 patent. The horizontal tie rod going through the center of each truss is not shown on the patent, although it is shown at the edge of the deck as a floor line tension rod. The new deck system consists of new hangers, floor beams, and a glue laminated wood deck with a blacktop overlay.
This was the first time this type of bridge was successfully dismantled and reassembled.
The bridge is on the National Register of Historic Places, and was documented as part of the Historic American Engineering Record program.
This project was awarded a 2008 Historic Preservation Award by the Historic Preservation Office of the New Jersey Department of Environmental Protection (see Rehabilitation of County Bridge C 0601). Some of the key people involved received award certificates.
Designer: Keller & Kirkpatrick
Contractor: Ferreira Construction Co.
To see pictures of the bridge taken before this work was done, see Neshanic Station Bridge.