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The Covered Bridges of Missouri: Union Covered Bridge

By: Clay Steward

Union Covered Bridge is located on the Elk Fork of the Salt River in southwestern Monroe County. It is the only example in Missouri of a covered bridge with the Burr Arch truss system. The bridge is 120 feet long, 17 feet and six inches wide, and has an entrance 12 feet high, which was just enough to admit a wagon load of hay. Union Covered Bridge was completed in 1871 and was named for the Union Church, which stood nearby.

On April 8, 1870, the Monroe County court authorized the funds necessary to construct a bridge over the Elk Fork of Salt River on the Paris to Fayette Road. Joseph Elliot, a bridge builder from Payson, Illinois, was chosen to build the bridge. Then as now, the county court was responsible for the maintenance of certain roads and bridges. Construction work was bid out, and the firm that offered the lowest price was generally chosen to do the work.

Union Covered Bridge has frequently been threatened by floods, fire and neglect. In 1967, the Missouri General Assembly passed an act declaring all remaining covered bridges in the state to be state historic sites and under the care of the state park system. After acquisition by the state, Union Covered Bridge was restored and repaired using part of the Mexico Covered Bridge, which had been washed away earlier that year.

The bridge continued to carry traffic until April 1970, when an overloaded truck broke one supporting beam and damaged three others while crossing the bridge. Since that time, the bridge has been open to pedestrian traffic only. On June 15, 1970, Union Covered Bridge was officially listed on the national register of historic places. To ensure its continued preservation, Union Covered Bridge State Historic Site is administered and maintained by the Missouri State Parks System.

For 14 months during 1987 and 1988, the Missouri State parks System and Prost Builders of Jefferson City worked together to complete a total restoration of Union Covered Bridge. A steel box truss was built through the bridge with huge counter weights on both ends. By using internal jacks, the center of the bridge was lifted 21 inches. This removed the sag from the bridge, brought all of the joints back into their original position and removed the tension that the timbers were under, making replacement of rotted timbers possible. A laser beam was installed to monitor progress during the lifting process. The bridge was raised approximately one inch each day. Several large timbers had rotted and were replaced. Today, with careful inspection, you can see them as less weathered than the older, original timbers in the bridge. During the restoration process, the oak clapboard siding was found to be so warped that replacement was necessary. At least three different types of siding were found on the bridge, indicating the three different periods when repairs were needed. On December 17, 1988, Union Covered Bridge was open again to the public.

Treenails, pronounced “trunnels”, were wooden pegs used in place of nails to hold the bridge together. Made on a lathe, they were anywhere from one to two inches in diameter and 10 to 12 inches long. As many as 900 treenials were used on a covered bridge 100 feet long.

Joseph Elliot used stepped scarf joints and lap joints to obtain the 126-foot-long upper and lower chords necessary in the construction of this bridge. A third joint, the mortise and tenon, can be seen where web members connect to the kingpost.

Each truss member was individually fashioned to fit a precise position. Elliot simplified the final assembly of the truss structure by stamping Roman numerals in the ends of the timbers to be joined..

Many covered bridges, including Union, are architecturally unique. Although there are other Burr Arch bridges in the country, not many of them are double Burr Arch trusses. Union is the only Burr Arch truss left in Missouri.

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