Bloomfield-Nulhegan River Route 102 Bridge

DESCRIPTION:

This bridge is located in Bloomfield Village, Vermont, on Vermont Route 102, over the Nulhegan River, near where it empties into the Connecticut River. This single span steel Pratt truss with riveted construction six panels rests on poured concrete abutments. The entire length of the bridge is 134 feet and the width is 24 feet. It clears the water by 10 feet and has a portal clearance of 15 feet. Still in use as a highway bridge in its original setting, the structure also maintains its integrity in engineering, materials, design, workmanship, feeling, association, and setting.

All of the connections on this span are hydraulically riveted, and most of the structural elements are rolled I-beams. Theses two characteristics are representative of the technological advanced and standardization associated with bridge construction in Vermont after 1927. The top chord has a latticed underside and its four panels are bisected diagonally by I-beams, which divide the panels into triangles. The center panels are bisected again, from the center of the diagonals to the lower corners.

The six panels consist of vertical, diagonal and sub-diagonal beams. The two end panels are triangular truss portal braces with channeled verticals. The four middle panels are bisected diagonally; the northern diagonals descend right to left, and the southern diagonals descend left to right. Sub-diagonals bisect the center panels from the center of the diagonals; the north panel has sub-diagonals from right to left, and the south has sub-diagonals from left to right.

There is a cross bracing at the top of each portal entrance, which connects both sides of the portal bracing. The braces consist of top and bottom chords connected by vertical and diagonal I-beams.

The floor system consists of I-beams mounted above the lower chord and riveted to the verticals. Four I beam stringers connect the beams and support a concrete slab floor. The guard rail is built up of angles and channels, with a pipe top rail. The horizontal rail spans the entire bridge, and is supported by vertical, waist high, evenly spaced beams. The entire structure rests on a poured concrete abutments which are located in the river banks, about ten feet above the water.

STATEMENT OF SIGNIFICANCE

The bridge on Vermont Route 102 over the Nulhegan River, near the Connecticut River, is located in Bloomfield, a small village in the northeast corner of Vermont. A steel truss bridge built in 1937, it is an excellent example of the Pratt through truss design, which was so popularly employed by Vermont state engineers in rebuilding the bridges that washed away in the disastrous flood of 1927. The structure qualifies at a state level under criterion "C" of the National Register because of its engineering significance. It represents the style, appearance, materials and engineering methods of industrial architecture in Vermont in the 1920's and 1930's. This bridge also signifies state historical patterns in government and transportation, making it eligible under National Register criterion "A". Vermont state government standardized the transportation industry after the flood, in an attempt to rebuild roads and bridges throughout the state as quickly and efficiently as possible. Prior to the disaster, local governments were responsible for bridge and road construction and repair. Nominated as part of a Multiple Property Submission, for Metal Truss, Masonry, and Concrete Bridges in Vermont, this bridge represents the steel truss bridge property type. Because it is an exceptional example of the Pratt through truss, and because it maintains its integrity in location, workmanship, design, materials, setting, feeling and association, the Bloomfield-Nulhegan Route 102 Bridge meets National Register requirements for listing as a steel truss property type.

The Bloomfield-Nulhegan Route 102 bridge represents the cumulation of the technological and engineering advances made in 1927, ten years before its construction. About 1200 bridges in the state had been destroyed by the 1927 flood, and the repair and reconstruction of these overpasses was an enormous project which had to be undertaken immediately. It was decided that steel truss bridges were the most expedient and practical to build, and so this became the standard type for all bridges in the state. Though metal truss bridge construction had been patented in the late 1800's, the engineering technology was still evolving in 1927, and Vermont became a national leader in the development of bridge technology and a laboratory for new construction and materials.

The truss bridge took many forms and designs, but the most popular type, and the type that was built in Bloomfield, was the Pratt truss. This type of truss was the most adaptable, and weight and stress distribution was most easily calculated for these bridges since they were so simple in design. The fact that the Pratt truss was so highly favored makes the Bloomfield-Nulhegan Route 102 bridge no less significant. In reality, the popularity of the Pratt truss represents its significant role in engineering history.

The arrangement of diagonal, sub-diagonal, and vertical beams and the designation of certain members as load and stress bearing sections in this bridge make it an excellent example of the Pratt truss design, It also uses the standard methods of construction that were used in 1927, when repairs were being made after the flood, and when the Pratt truss was at its height of popularity in Vermont. The flat chord Pratt truss was easier and more economical to build than the more complex and expensive curved Parker truss, and was the most practical type for Bloomfield.

Early truss bridges were assembled in a factory and then shipped to the site. Technological advances, such as rolled I-beams and hydraulic riveting machines enabled bridges to be entirely put together on site, which facilitated construction. These were recent innovations in the 1920's and Vermont was one of the earliest places in the nation to utilize this technology so frequently and effectively.

MAJOR BIBLIOGRAPHICAL REFERENCES

Historic Sites And Structures Survey, December 5, 1984, Bridge Survey Inventory Form. Survey Number 0501-22, conducted by Matt Roth, Historic Resource Consultants, on file at Vermont Division For Historic Preservation.

FORM PREPARED BY: Betsy Loftus, University of Vermont Historic Preservation, Wheeler House, South Prospect Street, Burlington, VT 05405. Tel: 802-656-3180. Date: 4/1/91. 1/23/94.)

DATE ENTERED: November 14, 1991.
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