UP Eagle Creek Bridge (Woolstock)

Located along County Road C70 on the north side of Woodstock, this unusual truss bridge carries a former Chicago & North Western Railway line over Eagle Creek. The first bridge at this location was likely a timber bridge, with a timber truss main span and timber pile trestle approaches. It is believed the first bridge had been periodically renewed since construction. During the early years of the 20th Century, the C&NW invested significant capital into this line, replacing timber bridges with heavier stone and steel structures. In 1902, a new steel truss bridge on stone piers was constructed to replace the center of the original bridge. Timber pile trestle spans were retained at either end, possibly to allow approach embankments to settle. The most recent alteration to the bridge came in 1914, when the timber spans were replaced by a deck plate girder and concrete abutments on each side of the truss. Between 1909 and 1917, the C&NW made a second round of improvements along this line, replacing most of the remaining timber bridges. Currently, the bridge consists of a 123-foot, riveted quadrangular lattice through truss span, set onto stone piers. The south approach consists of a 35-foot deck plate girder span, while the north approach consists of a 30-foot deck plate girder span. Both abutments are constructed of concrete, and the bridge is set on a sweeping 1.33-degree curve. An unknown contractor fabricated the truss span, while another unknown contractor fabricated the approach spans. Two separate unknown contractors also constructed the piers and abutments.

The truss span follows a somewhat unusual design, with heavily laced members and an unusual M-frame portal bracing. The top chord uses a built-up design, with V-lacing on both sides and thin plates on either side of the connections. The endpost is also composed of built-up beams, with X-lacing on the front and rear and thin plates at strategic points. The bottom chord is constructed of two U-shaped channels, which are joined by thin plates. The compression members are constructed of built-up tightly V-laced beams, while the tension members are composed of L-shaped bars. The floor system follows a standard design, with two plate girder stringers per track and plate girder floorbeams spaced at panel points. The portal bracing follows an M-frame design, which is constructed using V-laced beams. V-laced beams are also used for the sway bracing. T-shaped steel bars are used for both the upper lateral and lower lateral bracing. The deck plate girder spans follow a standard design, with two heavy plate girders and an open deck. Both are similar in design, using a diamond shaped structure founded on timber piles. Stone for the piers consist of a yellow limestone, likely quarried at Mankato, Minnesota. While no contractor has been confirmed for the piers, it is possible they were constructed by the Widell Company of Mankato, Minnesota. This company reportedly provided the C&NW with most masonry construction along the Iowa Division during the early 1900. The abutments use sloped wing walls, which extend at an angle from the structure.

The quadrangular lattice through truss design is relatively uncommon throughout the United States. However, a few railroads preferred the design, such as the Chicago, Rock Island & Pacific Railway (Rock Island), the Chicago & North Western Railway (C&NW) and the Chicago, St. Paul, Minneapolis & Omaha Railway (Omaha Road). Spans constructed in the late 1870s and early 1880s for the C&NW featured an arched and pedimented lattice portal bracing, light sway bracing and laced members. The second generation was nearly exclusively constructed by Lassig Bridge & Iron Works between 1884 and 1900, and featured heavier members and a decorative pedimented portal bracing. While the design fell out of favor for the Rock Island and Omaha Road around the turn of the 20th Century, the design remained popular with the C&NW into the 1920s. 20th Century versions of this design used significantly heavier members, were taller and contained no decorative features. 19th Century versions of this design were primarily constructed out of wrought iron, while 20th Century versions of this design were constructed of steel. The particular sub-design used here is unusual for the C&NW, and was only used at a handful of locations during 1901-02. The unusual design could possibly indicate that this span was fabricated by a company other than American Bridge Company. The C&NW preferred lattice truss designs, as they were both strong and demonstrated great resilience in case of a derailment. Since the 1914 reconstruction, the bridge has seen no significant alterations, and remains in use. 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.