Road: Route J
Feature Crossed: Little Niangua River
Other Location Information: approximately 7.6 miles NE of Mack’s Creek
Structure Number or County Bridge Number: Bridge No. S0391
Type: self-anchored suspension bridge
Length: 519’ 10” (450’ suspension span with 225’ main span; 69’ approach span)
Width: 20’ curb-to-curb; 24' 11" out-to-out
Year Built: 1933
Builder: Clinton Bridge Works, general contractor
Current Load Rating: Weight limit 15 tons
History of Modifications, Rehabilitations, etc.: 1997 timber deck replaced with steel grid deck
For further information, please contact:
Name: Karen Daniels, Sr. Historic Preservation Specialist
Organization: Missouri Department of Transportation
Address: MoDOT Design Division, Historic Preservation Section, P.O. Box 270, Jefferson City, MO 65101
The Little Niangua River Bridge (S0391) is a self-anchored suspension span carrying Route J across the Little Niangua River. The bridge is 519’ 10 ½” long with one 70’ steel girder approach span. The three main suspension spans are side Span 1 (112’ 6”), Span 2 (225’) and side Span 3 (112’ 6”). The substructure consists of one “U” abutment, one open abutment, two piers and one bent. The superstructure has two portal towers with saddles caring the main cables; the vertical clearance over the roadway is 14’ 11”. There are four main pre-stressed parallel strand cables which carry the hangers. The bridge has a 20’ steel open grid deck roadway with 2’ 6” curbs, and two tier channel railings.
In 1931, Camden County, Missouri was given $25,000 as mitigation for the construction of the Bagnell Dam. The County decided to put a bridge over the Little Niangua River. The County approached the Missouri State Highway Department (MSHD) about building the bridge. The MSHD agreed to assist the County, and consulted with the John A. Roebling’s Sons Company of Trenton, New Jersey about building a suspension bridge. Following the discussions, the MSHD finalized plans for a self-anchored suspension span. Bids for the project were due on May 5, 1932, but the lowest bid was rejected and new bids were accepted on June 7, 1932. The contract was awarded to the Clinton Bridge Works of Clinton, Iowa, for $32,980. The contractor used the west bank of the Little Niangua River to stage construction and began with the driving of a falsework trestle. Substructure construction began on August 1, 1932, beginning at the east abutment. Work proceeded toward the west utilizing the trestle. Work on the superstructure started on February 1, 1933, and was completed March 25, 1933. The project was inspected and accepted by the MSHD on March 27, 1933.
The Bridge was determined eligible for listing on the National Register of Historic Places under Criterion C for engineering as a nationally significant example of a self-anchored suspension bridge. At the time of its erection it was one of four self-anchored suspension spans, with the other three located in Pittsburgh, Pennsylvania. The difference between a self-anchored suspension bridge and a suspension bridge is that a self-anchored suspension bridge does not need massive anchorages. The main cables are secured to the stiffening girder which carries the horizontal component of the cable tension; in turn, the end supports only have a vertical component of tension. The Little Niangua River Bridge is significant because of its construction as a self-anchored suspension bridge, anchoring to a stiffening girder and its use of pre-stressed cables for the hangers. Shortly after its construction, articles about the engineering of the bridge were published in the Engineering News Record and in Suspension Bridges of Short Span by the American Institute of Steel Construction.
MoDOT’s Historic Preservation Section is now accepting proposals for the reuse of the bridge in its existing location until October 31, 2017. If no proposals for reuse in the existing location are received, proposals for relocation of the bridge will be considered. A proposal checklist is available MoDOT’s Free Bridges website. Preservation covenants may accompany the bridge.