Porlier Street Railroad Bridge

Located at Porlier in Green Bay, this large through truss swing bridge once carried the former Chicago, Milwaukee, St. Paul & Pacific Railroad (Milwaukee Road) mainline over the Fox River. The first bridge at this location was likely a timber swing bridge, constructed when the line was first built. In 1881, the first bridge was replaced by a 204-foot combination Howe through truss swing span, set onto timber pile piers and approached by timber pile trestle spans. Wooden trusses were commonly used by railroads for early bridges, as they were inexpensive and easy to construct. By the turn of the 20th Century, wooden truss bridges had become obsolete for most railroad uses, and railroads sought to replace the structures with modern steel structures. In 1901, the Milwaukee Road began planning a replacement bridge at this location, and the structure was completed in 1902. The bridge consisted of a 201-foot, 8-panel, riveted rim-bearing Warren through truss swing span, set onto concrete piers and approached by timber pile trestle spans on either end. The replacement of this bridge came at a time when the Milwaukee Road was upgrading many of its outdated timber swing bridges in northeast Wisconsin. A similar bridge was constructed at Oshkosh, Wisconsin in 1904. Typical of Milwaukee Road designed swing spans from the era, the truss made extensive use of built-up members, used a decorative lattice portal and used a unique end lift mechanism.

The top chord and endposts were both constructed with built-up beams, with X-lacing on both sides. The bottom chord was also composed of a built-up beam, with X-lacing on both sides. The diagonal members were constructed of built-up beams, which also used X-lacing; while the vertical members were constructed of solid rolled beams. Similar to other swing spans from the era, the main span was composed of two 4-panel halves, joined over the center pier by a center tower. This center tower used a rectangular shape, and was mainly constructed out of built-up beams composed of X-lacing. Two levels of struts were used at the center tower, and were composed of X-laced beams. The upper lateral bracing of the tower was composed of a similar design. To stabilize the tower, steel rods were used for longitudinal bracing, creating two levels of "X" shapes. These rods were connected to the vertical members of the tower by use of pinned connections. An additional transverse bracing was located on both sides of the tower between the two levels of struts, which used L-shaped bars riveted to the vertical members. The center tower was connected to the upper angles of each leaf by use of heavy eyebars, which were pinned at both ends. An upper lateral bracing between these eyebars was composed of thin rods with a hook shape, which were pinned at each end. The portal bracing used a standard Milwaukee Road design for the era, with a double intersection lattice beam and rounded heel bracing with a star cutout. Similarly, the sway bracing used a double intersection lattice beam, but omitted the heel bracing. The floor was composed of two heavy plate girder stringers and plate girder floorbeams at the panel points, typical for spans from this era. Both the upper lateral bracing and lower lateral bracing consisted of L-shaped steel bars. The center pier consisted of a circular concrete structure, while the outer piers used a rounded rectangular shape.

To operate, the swing span used a standard rim-bearing design with a unique end lift mechanism. A rim-bearing span operates by placing the superstructure on a metal drum, which rotates on a roller nest located on the center pier. A gear system drives the drum and turns the bridge. Typical of Milwaukee Road swing spans, the center drum used a circular design and was constructed of plate girders. In addition, the superstructure used a heavy square floor section to connect to the drum. When operating, the rail lifts at the end of the bridge are first operated. A pin at the center of the track maintained the proper alignment of the bridge, and a series of radial plate girders or rods extended from the center of the track to the drum girder. The main disadvantage of this design is the bridge must be constructed nearly flawlessly to avoid shifting. These mechanisms lift the rail, and allow the bridge to swing freely. Next, the locking mechanism is lifted, and the span is rotated slightly, before the operator engages the motor of the rotating mechanism. The operator then stops the rotation by cutting power to the motor or by applying a brake. Many traditional swing spans use wedges driven at the end to lift the span after the locking mechanism was disengaged. The Milwaukee Road designed a different mechanism for this function. At the end of the span, a cam shaped end lift shoe rotates about an axis perpendicular to the railroad, causing the span to raise or lower. In closed position, this shoe acts as a rocker bearing, absorbing small expansions and contractions. A shaft running longitudinally under the bridge carried power from the motor to the end shoes. This bridge was electrically operated, with the machinery located within a wooden house at the center of the span.

An unknown contractor fabricated the superstructure. A bill of materials indicates that Phoenix Bridge Company fabricated the shafts for the end lift mechanism, but is unclear if this company also fabricated the remainder of the bridge. Typical of Milwaukee Road bridges, the concrete substructures were constructed by employees of the Bridge & Building Department. Riveted Warren truss spans became popular in the early 20th Century as an alternative to pin-connected Pratt truss spans. This pattern provided greater strength and rigidity, while maintaining a simple and economical design. It appears that the Milwaukee Road adopted Warren truss spans in late 1901 or 1902 as evidenced by other bridges designed by the railroad. This span may have been among the first designed by the Milwaukee Road to use the Warren design as part of a movable bridge. After the bridge was abandoned in the 1990s, the swing span was placed into open position to allow for river navigation. In approximately 2005, the eastern approach was converted to the "Porlier Pier", a fishing pier extending into the river. Due to Coast Guard requirements to remove abandoned bridges over navigable waterways, the swing span, west approach and associated piers were removed in October 2014. The removal of this bridge resulted in the loss of the oldest movable bridge across the Fox River in Green Bay. In 2022, the eastern approach was closed to pedestrians due to advanced deterioration to the timber components. The City of Green Bay later decided to remove the approach and replace it with a fishing pier. As of 2025, the approach is still standing, and the replacement is under design. Overall, the main span of the bridge was in fair to good condition at the time of removal, and its removal was due to Coast Guard regulations instead of poor condition. The author has ranked this bridge as being moderately significant, due to the truss and movable design.