This looks to have originally been some other design, possibly a wooden stringer, sometime in its history it has been modified to its current configuration
Dimensions
Length of largest span: 12.1 ft.
Total length: 24.9 ft.
Approximate latitude, longitude
+35.05433, -84.73193(decimal degrees) 35°03'16" N, 84°43'55" W (degrees°minutes'seconds")