Gotch Park Trail Bridge

Located south of Humboldt in Frank Gotch State Park, this attractive Pratt through truss bridge carries a former Minneapolis & St. Louis Railway line over the East Fork Des Moines River. The first bridge at this location was likely a wooden truss bridge, set onto timber pile substructures and approached by timber pile trestle spans. In 1891, the first bridge was replaced by a 159-foot truss span, set onto stone piers and retaining the approach trestles on either end. Little is known about this bridge, although it is believed that the truss was also a wooden truss span. Between the late 1890s and early 20th Century, the M&StL made significant improvements to their lines, replacing wooden bridges with steel, stone and concrete structures. In 1901, the present bridge at this location was constructed. Currently, the bridge consists of a 159-foot, 6-panel, pin-connected Pratt through truss span, set onto stone piers. The east end (railroad south) is approached ten timber pile trestle spans, while the west end is approached by three timber pile trestle spans. Detroit Bridge & Iron Works fabricated the truss span, while the timber components were constructed by railroad company forces. The stone piers were reused from the 1891 bridge, and were constructed by an unknown contractor.

The truss span follows a standard pin-connected Pratt through truss design, with the addition of a decorative portal bracing. This span uses built-up members, a standard floor and an attractive lattice portal bracing. The bottom chord consists of eyebars, with one set at the outer panels and two sets at the inner panels. The vertical members consist of built-up beams, which are formed out of two U-shaped channels and conencted by a tight V-lacing. The diagonal members consist of eyebars, while the counters use slender steel rods with turnbuckles. The floor system follows a standard design, with two plate girder stringers and plate girder floorbeams. The portal bracing uses a deep lattice design, with triangular lattice heel bracings. The sway bracing is much more simple, with a V-laced beam and diagonal bars connecting to the vertical members. Both the upper and lower lateral bracing consist of square steel bars. The piers also follow a standard design, consisting of rectangular structures with an angled upstream nose. Stone for the piers consists of a tan limestone, quarried at an unknown location. The timber trestle approaches follow a standard M&StL design, with six stringers arranged into two sets of three. The timber components were likely last renewed in the mid-20th Century.

Pratt trusses were arguably the most common railroad truss bridge design during the second half of the 20th Century. This design was simple, economical and durable. By the turn of the 20th Century, railroads began switching to riveted Warren truss spans. The M&StL had relatively few truss spans on the system, and there was not a standard design followed. Out of the handful of through truss spans constructed prior to 1910, there was a number of both pin-connected Pratt spans and early riveted spans. Of the pin-connected Pratt spans, no two spans were identical, and each had slightly different features. Since the initial construction, the bridge has seen no significant alterations. After abandonment, the bridge was acquired by Humboldt County, and converted to trail use. A wooden deck and handrails were added, and the structure now serves a short segment of the Three Rivers Trail. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being moderately significant, due to the truss design.