WSOR Wisconsin River Bridge (Spring Green)

Located east of Spring Green, this large through truss and plate girder bridge carries the former Chicago, Milwaukee, St. Paul & Pacific Railroad (Milwaukee Road) across the Wisconsin River. Typical of many Milwaukee Road bridges over large water bodies, this bridge was constructed in sections at different times. It is believed that the first bridge at this location consisted of a wooden truss bridge, approached by timber pile trestle spans. The center span of this bridge was likely a swing span, as the Wisconsin River was navigable at this location. Railroad records indicate that the swing span was replaced with a 205-foot iron through truss swing span in 1876. This span likely used a Pratt design, and was likely lightly constructed. As the channel shifted east in the early 1880s, two additional 67-foot Howe pony truss spans were installed on the east approach in 1884. The next major rebuild of the bridge came in 1886, when much of the approaches were reconstructed. On the east end, a skewed 105-foot, 6-panel, pin-connected Pratt through truss span was installed. Following the pony truss section, a skewed 102-foot, a 106-foot and a 105-foot span of the same design were installed adjacent to the swing span. West of the swing span, a 106-foot, 6-panel, pin-connected Pratt through truss and a 120-foot, 7-panel, skewed span of the same design were installed. These spans used a light design, with light built-up members and a lattice portal with decorative cast rosettes. In addition, new stone piers were installed for the spans.

By the late 1890s, the swing span had become too light for traffic, and a new steel through truss swing span would be installed in 1899. In 1905, the two pony truss spans were replaced by secondhand deck plate girder spans. The eastern of these two spans was a 60-foot deck plate girder, originally fabricated in 1902 by the Wisconsin Bridge & Iron Company for Bridge #I-1070 across the Skunk River near Rubio, Iowa. The 75-foot deck plate girder span was originally fabricated in 1883 by an unknown contractor for Bridge #Z-284 over Killbuck Creek near Davis Junction, Illinois. The 75-foot span was cut down from its original 80-foot length, and both spans were converted to skew spans. The bridge remained in this configuration until 1927, when it was decided to replace some of the approaches with new spans. The 105-foot truss span east of the swing span was replaced by a pair of through girders, and the two truss spans west of the swing span were replaced by a pair of secondhand through truss spans. At this time, old piers were repaired and new piers constructed for the new configuration. A 105-foot span was confirmed to have been reused at Bridge #M-502 across the Chippewa River at Dunnville, Wisconsin. It is believed that the 120-foot and a 106-foot span were relocated to Bridge #F-182 across the Pecatonica River near Browntown, Wisconsin. In 1944, the bridge was further altered, when the eastern approach span was replaced by timber pile trestle, and the remaining two 1886-era truss spans were replaced by three deck plate girder spans. At this time, additional piers were constructed. The most recent alteration came in 2017, when the timber pile trestle approaches were replaced by steel stringer spans, giving the bridge its present configuration.

Currently, the bridge consists of a number of different spans, constructed at different times. The east approach consists of a 22-foot, two 30-foot and a 20-foot steel stringer span, set onto steel pile and concrete substructures, and constructed in 2017. The main portion of the bridge consists of a 60-foot deck plate girder span, a 75-foot deck plate girder span, two 70-foot deck plate girder spans, a 68-foot deck plate girder span, two 53-foot through plate girder spans, a 205-foot swing span and a pair of 112-foot 6-inch through truss spans. These spans are set onto a combination of concrete and stone masonry substructures. The west approach consists of a 22-foot steel stringer span, 28 32-foot steel stringer spans and a 22-foot steel stringer span, set onto concrete substructures and constructed in 2017. With the exception of the swing span and approaches, it is believed that the remaining steel spans were reused at this location from other places. Railroads commonly reused steel and iron spans, as it provided a cost effective way to replace branch line bridges without requiring large amounts of new material.

The 60-foot deck plate girder span (span #1) consists of a standard deck plate girder design, with two heavy girders and an open deck. Due to the geometry of the river, the west end of this span has been altered into a skew. This span appears to have originally been fabricated in approximately 1900 by an unknown contractor, and was reused from an unknown location. The 75-foot deck plate girder span (span #2) consists of a slightly more unusual design, with two heavy plate girders and an open deck. The ends of these girders use a taper, giving the span a "fishbelly design". This type of girder was typically used where the piers were too tall and could not easily be altered. This span also appears to have originally been fabricated in approximately 1900 by an unknown contractor, and was reused from an unknown location. These two spans were erected at this location in 1927-1928. The two 70-foot deck plate girders and the 68-foot deck plate girders (spans #3, #4 and #5) all appear to use an identical design, with heavy girders and an open deck. These spans also appear to have been fabricated in approximately 1900 by an unknown contractor, and all three spans were likely reused from the same location. The two 53-foot through plate girder spans (Spans #6 and #7) consist of standard type "C4" through plate girders, constructed in 1927 by the American Bridge Company. These spans use modest sized girders with rounded ends. "C4" girders used two stringers per span, a typical through girder design.

The swing span (span #8) consists of a large 205-foot, 13-panel, pin-connected Pratt through truss span, fabricated in 1899 by an unknown contractor. The span is constructed with a rim bearing design. A rim bearing swing span is constructed by placing the superstructure on a metal drum, which rotates around a nest of rollers on a track. The span is operated by a gear system, which rotates the span. The truss uses a somewhat unusual design for the era, with one continuous span balanced on the drum instead of two halves. Many of the features of this span are typical of late 1890s and early 1900s Milwaukee Road truss spans. The top chord and endposts are constructed of built-up members, which use a plate on the exterior and X-lacing on the bottom. The bottom chord is constructed exclusively of X-laced beams. Similar to other Milwaukee Road truss spans from this era, the vertical members are composed of built-up beams, composed of two channels connected by evenly spaced plates instead of lattice. Diagonam members on the span are composed mainly of steel bar and rod eyebars, which are connected by turnbuckles. Diagonal members at the towers are constructed of built-up beams, similar to the vertical members. The floor system is heavily constructed, with the bottom chord placed above the tracks. This floor system is composed of stringers and plate girder floorbeams. Vertical members are affixed to the top of the floorbeams, and the bottom chord rests on the top of the floorbeams. The portal bracing consists of a typical lattice beam, with curved heel bracing. The sway bracing consists of a shallow lattice beam, which is connected to the vertical members by diagonal bars. The top lateral bracing is constructed of square steel bars, which are screwed into clamps, which are pinned to plates in the top chord. It is unknown how much of the original operating machinery of this span remains intact, although the drum, roller nest and end rollers are still intact. It is unlikely that this span has turned in the last century.

The two west truss spans (spans #9 and #10) consist of 112-foot 6-inch, 5-panel, pin-connected Pratt through truss spans, originally fabricated by the Lassig Bridge & Iron Works in 1895. These spans use a standard 1890s design for the Milwaukee Road. The top chords and endposts are comprised of built-up channels connected by plates on the exterior and X-lacing on the bottom. The bottom chords are composed exclusively of built-up beams with X-lacing. A portion of the top chords have a splice plate, possibly indicating the span was shortened. The vertical members of the spans are constructed of channels with a tight V-lacing. Typical for truss bridges from this era, the diagonal members are composed of slender bars. There is further evidence of alterations, as one set of diagonal members on each span has been spliced above the turnbuckle by use of additional bars. The floor of these spans uses a more traditional design, with floorbeams set above the bottom chord. The floor is comprised of two stringers and plate girder floorbeams, which are riveted into the sides of the vertical members. The Portal bracing on the span uses a lattice design, with a rounded solid plate for heel bracing. The sway bracing uses a V-laced bar, with diagonal bars connecting to the vertical members. The upper lateral bracing is composed of thin rods, which are screwed into hooks, which are pinned to the tops of the sway and portal bracing. An identical span at Bridge #G-388 across the Wisconsin River at Merrill, Wisconsin was installed in 1929; and a second identical span was installed at Bridge #Y-136 near Jefferson, Iowa in 1930, likely indicating a connection between these spans. While the author cannot confirm where the spans may have come from, it is possible that they were originally constructed for Bridge #I-702 across the Grand River at Chillicothe, Missouri and shortened upon relocation. This bridge originally consisted of four 135-foot, 6-panel, pin-connected Pratt through truss spans, fabricated in 1895. By removing one 22-foot 6-inch panel, this would provide the current 112-foot 6-inch length.

The main substructures consist of a combination of concrete and stone construction. The eastern pier (pier #1) and pier #2 were both renewed in 1942 to replace failing concrete piers. These piers use a rounded design, typical of 1940s Milwaukee Road concrete piers. Piers #3, #4 and #5 all consist of square concrete piers, also constructed 1942. Piers #6, #8 and #10 all are constructed of stone, which was encased in concrete in 1927. Pier #6 likely dates to 1886, while piers #8 and #10 likely date to 1876. The swing pier, pier #9 consists of a round stone pier, which likely dates to 1876. Piers #11 and #12 both were constructed in 1927, and consist of concrete. These piers were encased in new concrete as part of the 2017 rehabilitation. All approach piers are constructed of steel pile bents with a concrete cap, and both abutments are constructed of concrete.

While reusing spans was a common technique for railroads, it is somewhat uncommon to see a variety of spans like what is present on this structure. These spans represent different types of construction and different eras of technology. The truss spans have some different evidence of strengthening, such as additional plates and some rivets replaced with bolts. Pratt trusses were arguably the most popular truss bridge design in the second half of the 19th Century. These spans combined economy, strength and simplicity. This design largely fell out of favor by the early 20th Century, as riveted Warren trusses became the new standard. Plate girder spans were commonly used by railroads, as they were durable and easy to construct. Overall, the bridge appears to be in good condition, and the recent alterations have likely extended the life of this bridge. The author has ranked this bridge as being regionally significant, due to the diverse mix of spans, ages and unknown history.