Presented by:
J M Hillman, PE & LS
Master Bridge builders John Godwin and Horace King introduced to Georgia, Alabama and Mississippi a type of bridge design that employed the Town Lattice Truss. The truss design itself was developed by Connecticut architect Ithiel Town. His first bridges, spanning the Connecticut River, employed the Burr Arch Truss, a design relying on heavy arches that were difficult and expensive to construct. In search of a less expensive truss design, Town devised his own system, patenting it in 1820.
Town's system employed ordinary sawmill lumber, criss-crossed like a garden trellis, double pegged at each intersection and stiffened at the top and bottom by long horizontal chords. The resulting trusses formed, in effect, a ribbon of interlocking triangles capable of supporting tremendous weight without sagging, even over spans of 120 feet.
Employing Town's design, local carpenters could easily build single span bridges over small creeks. But for major river crossing, four hundred to six hundred feet in length, master bridge builders were needed to survey and measure the location, to calculate materials, to oversee construction and to elicit precise workmanship from laborers, both free and slave. Horace King, who worked for some twenty years with John Godwin and more than thirty years on his own, excelled at such tasks.
The process which King and other bridge builders employed, according to covered bridge historian Herbert Wheat Congdon, may have been similar to this:
The timbers for the bridge were laid out on an open field near the site. Here the master builder would assemble a panel or part of the frame, probably marking his line with a scrawl or sharp bladed knife, rather than a pencil for greater accuracy. Patterns or templates were carefully copied from this sample for use by the laborers in cutting. Even a trifling error at this point could result later in a sag or a weakening of the truss, and a shorter life for the bridge.
The parts were connected by oaks pins, termed treenails (pronounced trunnels), which were often soaked boiled in oil to assure durability. The large truss timbers were arranged on the ground and leveled, and holes were bored for the pins. Again the accuracy was essential. The Clarkson bridge departs from the early designs by the use of iron carriage bolts in lieu of oak treenails. Many of the bolts have been removed over the years by souvenir seekers. These bolts must be replaced along with damaged upper and lower chords.
While this work was underway, other laborers erected bridge abutments in the stream and constructed scaffolding, laying first the large timbers or stringers, the length of the span. This was a particularly delicate task, for the stringers had to be set with camber so that the middle of the span was several inches higher than the ends, allowing for the inevitable settling that would occur later.
If all went well when the bridge was completed and the last of the scaffolding was removed, the bridge would settle a little and all of the parts would tighten into an enduring whole. But if the builder had made an error in his computations, or if his workers had been careless, the bridge might show the effects immediately. When the bridge was completed and the falsework removed, the builder himself would make the first trip across the bridge in a fully loaded wagon. The structure would come alive with the solid sound of wood against wood as its camber resisted the load. At least one builder was heard to mutter as he headed across his bridge "If she goes, I'll go with her."
During his lifetime Horace King, employing the Town truss design, oversaw the construction of more than twenty five bridges 500 feet or longer and perhaps a hundred or more lesser spans. On their strength and endurance he made his reputation.
The Clarkson Covered bridge is located off Highway 278 near Bethel. The 250 feet, two span Town Lattice Truss stretches high above Crooked Creek. Clarkson Bridge was built in 1904 on land originally by J W Legg. Mr. Legg sold the property to the county and the eventual construction of the bridge cost $1500. In 1923 a storm blew half of the bridge downstream. Fortunately the part that fell in the creek became lodged and the citizens of the Cullman area were able to salvage the materials. The county hired a contractor to restore the bridge at a cost of $1500.
