Wells Street Bridge: A Rebuilt Bascule Bridge Defines Chicago’s Infrastructure and Civic Symbolism

Article and photographs by Divi Logan

About the Wells Street Bridge

The original Wells Street Bridge opened in 1922. In 2012 – 2013 the bridge was rebuilt. It is one of two bridges in downtown Chicago that carries Chicago Transit Authority trains on its upper deck, the other being Lake Street Bridge across the river’s south branch.

Bridge specifications and details:
Fixed trunnion
Truss Type: Warren through truss bascule
Decks and leaves: Two decks, two leaves
Carries: trains on the upper deck, vehicles and pedestrians on the lower deck
The bridge’s double-deck, double-leaf bascule design includes complex truss work with built-up members fabricated by the Fort Pitt Bridge Company.

I. Approaching the Bridge: Superstructure, Train Decks, and Clear Span

Wells Street Bridge clear span — The entire span, clear span, and south train deck approach span are shown here, looking east from the Franklin Street Bridge.

The civil engineering challenges of the Chicago River’s winding courses and shallow depths required the use of movable bridges to accommodate the city’s growing population, commercial shipping industry, and social connections. Many styles of bridge were tried, such as the swing and rolling lift. Center-pier spans interfered with navigation.

Clear span with Warren through truss structures, and a crossing train. Part of the south train deck approach span is shown to the right.

The challenge was answered starting around 1900 with the building of trunnion bascule bridges, defined as bascule (French for “seesaw” or balance scale), and the trunnion, which is the large axle that raises the span. The Chicago-style bascule bridge is a refinement by Joseph Strauss of the fixed-trunnion. Design variations noted in the city include the single-deck pony truss and the style discussed in this article, the double-deck, double-leaf, Warren through truss.

The Through Truss Bridge: Heavy Metal Connects Chicago Infrastructure

Wells Street Bridge north tender's house — Superstructure and north tender’s house, from near the Merchandise Mart.

Through truss bascule bridges are connected by top and bottom chords, the longitudinal members that define the top and bottom edges of the truss. Top chords are in compression on the upper boundary, and bottom chords are usually in tension, forming the lower boundary. These are subject to significant stress during bridge operation.

Bridge superstructure showing subdivided Warren truss, substructure, north abutment, fenders, and a crossing train, viewed from the Riverwalk.

Many elements are shown here: intermediate bracing along the north leaf, sidewalk cantilevers, X-bracing, a barricade arm, deck lighting, part of an abutment, the clear span’s decorative railing, and part of the Merchandise Mart Brown Line station. Intermediate bracing is displayed along the inner portion of the leaf.

In double-deck configurations, bracing helps transfer loads between the upper and lower decks.
It ensures that live loads (vehicles, pedestrians) are not concentrated on isolated members, reducing fatigue and stress concentrations.

Wells Street Bridge north leaf and bridge tender's house — The north leaf is shown here with a bridge tender’s house, abutments, and fenders on either side of the abutments. The bridge pit that houses the counterweight is also shown, with its substructure bracing.

Train deck approach span for the south leaf. It is in the standard Warren truss design without the vertical divisions. Gusset plates anchor the structural members together.

Elements along the north leaf area are parts of the train deck approach span connecting to the Brown Line station, warning lights, the southbound portal, part of the clear span, and barricade arms that are lowered during bridge lifts.

II. Top and bottom chord photographs.

These photographs display critical structural elements of the bridge: gusset plates, rivets, nuts and bolts, X-bracing, lateral bracing, and the road deck.

Through the axis of the bridge during bridge lifts or from sidewalks, bottom chord connections are notable in the parallel bracing and gusset plates at the nodes towards the clear span portion of the superstructure.

Wells Street Bridge. Chicago, Illinois. — The Wells Street Bridge (original, 1922; rebuilt 2012 – 2013) exhibits longitudinal symmetry along its steel structure. The lines of the structure create a vanishing point in the center of the image. All elements of the bridge are symmetrical including trusses, bracing, beams, lanes, sidewalks and railings. Also shown are nodes, where truss beams connect to the bottom chord. This is the only time it is safe to look north along the bridge, during times when it is closed to allow the leaves to be raised for the passage of watercraft.

II A. Top chord

top chord connections on the Wells Street Bridge in Chicago — Top chord connections, batten plates, gusset plates, intermediate bracing, and part of protective rail near the gear rack on the south leaf.

II B. Bottom chord

At the bottom chord are connections called nodes. These are key points in the bridge’s geometry or load path. In engineering and architectural analysis, a **node** refers to: **junction points** where two or more structural elements meet (e.g., beams, girders, trusses). A **location of force transfer**, such as where loads are applied or reactions occur. A **pivot or hinge point** in mechanical systems, especially in movable structures like bascule bridges. The view looks east along the south leaf.

Bottom chord connections, gusset plates, and weights stacked in a diagonal beam at a gear rack. The view looks west.

bottom chord of the Wells Street Bridge — Bracing along the bottom chord of the bridge.

III. Bridge Tender’s Houses

Bridge tender’s houses are part of the rich history of Chicago’s waterway infrastructure. They serve as control centers for operating bascule bridges, housing the equipment and personnel needed to raise and lower the bridge leaves.

These structures are integral to the mechanics and management of movable bridges, especially in cities like Chicago where river traffic intersects with dense urban infrastructure.

The bridge tender’s houses exhibit a mélange of features of the Art Deco design era plus elements from classical antiquity. Art Deco flourished in the 1920s, a significant period of construction in Chicago. The diverse styles that influenced it had already appeared in the mid-19th century.

North house with bell, 1922 plaque, and superstructure level foundation. They are constructed of Bedford limestone, a popular building material for Chicago structures in the 1920s.

Features of Art Deco on the bridge houses include vertical emphasis, clean lines, simple shapes, elegant simplicity and a streamlined look, and the use of luxurious materials.

Wells Street Bridge south bridge tender's house — South house with plaque, bell, and superstructure level foundation. Design features from classical antiquity are the guttae along the lower edge of the roofline, and mirror symmetry. Guttae are the small conical drops that are meant to repel water. Quality stonework is essential for the masonry of structures for Chicago’s bridges.

South leaf house viewed during a riverboat cruise. The train deck approach span is designed with the standard Warren truss.

The tiled roofline of the south bridge tender’s house displays an interesting vent decorated with a carved shell and scrolling elements.

IV. Engineering and Structural Details: Bracing, Plates, and Supports, and Substructure

This view of the clear span includes elements of the superstructure and precision engineering in the substructure. Features include sidewalk cantilevers, X-bracing, gusset plates, the north abutment and bridge pit.

The substructure of a bascule bridge includes elements like sidewalk cantilevers, stringers, floor beams, bridge pits, and abutments.

Wells Street Bridge substructure — West elevation view from the Riverwalk: substructure bracing, sidewalk railing, substructure with train deck, and north bridge tender’s house with abutment.

Wells Street Bride substructure — Substructure elements include intricate X-bracing, sidewalk cantilevers, floor beams, and stringers.

Movable Leaf: On a bascule bridge, stringers are part of the rotating leaf. They must be precisely aligned to avoid interference with the counterweight and trunnion mechanisms.
Deck Support: Often topped with steel grating or concrete panels, stringers anchor these surfaces securely while allowing for drainage and thermal expansion.

IV A. Intermediate and Lateral Bracing

Intermediate bracing serves several critical structural and operational functions on movable span bridges. They resist torsional and lateral deformation when the leaves are raised, and the trusses are cantilevered and vulnerable to lateral wind loads.

Intermediate bracing helps maintain geometric alignment between the two leaves, especially critical at the center lock.
Misalignment can cause locking failures or uneven wear on mechanical components.

Wells Street Bridge center — Bracing at the center of the bridge, and Warren through truss top chord connections. Telephoto at left; from along the sidewalk at right, looking east.

IV B. X-bracing

X-bracing on double-deck bascule bridges like the Wells Street Bridge serves a crucial structural and functional role, especially given the complexity and mass of these movable spans.

Primary functions of X-bracing

X-bracing resists transverse loads—such as wind, vibration from trains, and dynamic forces during bridge movement.
On double-deck configurations, the upper deck (CTA trains) and lower deck (vehicular/pedestrian traffic) introduce differential loading, making lateral reinforcement essential.

X-bracing on the substructure of Wells Street Bridge — X-bracing on the bridge’s substructure, with gusset plates and stringers.

The crisscross pattern helps distribute vertical and horizontal loads across the truss system. It reduces stress concentrations at joints and riveted connections, especially near the trunnion bearings and counterweight housings.

Functions for Torsional Rigidity

Double-deck bascule bridges are susceptible to torsional forces due to asymmetrical live loads (e.g., a train on one side, cars on the other)

The X-bracing is especially prominent in the vertical truss panels and portal frames, reinforcing the bridge against the dynamic loads of elevated rail traffic and frequent leaf operation.

This is especially useful in shorter or less heavily loaded members, where full lacing would be excessive or visually disruptive.
They reduce the risk of stress concentrations at rivet points or junctions, especially near gusset plates and panel points.

North leaf portal and train deck approach span X-bracing, stringers, gusset plates, and a gear rack.

During leaf rotation, the bridge experiences non-uniform stress across its span. X-bracing stabilizes the structure while the leaves pivot, especially in the approach spans and fixed trunnion zones.

X-bracing, steps to and part of the inspection catwalk, road deck, sidewalk, and lighting

IV C. Batten Plates and Gusset Plates

The word “batten” may be familiar in the phrase “batten down the hatches.” Its origins are from the use of strips of wood or bars nailed across parallel boards to hold them in place. There is the nautical sense of using strips of wood and tarpaulins over a ship’s hatches to prevent leakage in stormy weather.

Gussets were parts of suits of armor in the area of the arms. In a sense of use on a steel bridge, the idea of holding metal pieces together is logical. Gusset plates on a bascule bridge join the truss elements together at key junctions. These precision – engineered plates resist dynamic loads during bridge lifting and lowering.

Gusset plates, batten plates, and X-bracing at the top chord. and a batten plate on one of the diagonal panels. The beams display thousands of nuts, bolts, and rivets.

South leaf portal gusset plates, intermediate bracing and X-bracing, and gear rack on the southwest corner, with a CTA train crossing between the clear span and the train deck approach span.

Superstructure X-bracing along the top chord and beams near the south leaf gear rack

Gusset plates, intermediate bracing, X-bracing, rivets, nuts and bolts near a gear rack.

bottom chord and gusset plates on the Wells Street Bridge in Chicago — Gusset plates connect at the bottom chord, along with X-bracing and rivets.

Batten plates on the Wells Street Bridge—and similar riveted truss structures—play a subtle but essential role in maintaining the integrity of built-up members. They are used to tie together individual elements (typically angles or channels) that form a built-up compression member.

On the Wells Street Bridge, these are often seen in vertical and diagonal members of the truss, where multiple steel shapes are riveted side-by-side. The plates prevent buckling or lateral displacement of these elements under compressive loads.

Close-up of a batten plate. The origins of the word “batten” may stem from Old Norse *batna* (“to grow better, improve, recover”), from Proto-Germanic *batnaną (“to become better, improve”) (compare Old Norse *bati* (“advantage, improvement”).

Batten plates anchor diagonal beams and the top chord in this north-facing view.

Batten plates and X-bracing near the north leaf portal and train deck approach span.

IV D. Road Deck Structures, Floor Beams, Stringers, and Cantilevers

Stringers are longitudinal beams that run parallel to the direction of traffic. They sit between the main girders and support the deck, transferring loads from the deck to the floor system and ultimately to the substructure.

Load Distribution: Stringers carry live loads (vehicles, pedestrians) and distribute them to floor beams and girders.
Flexibility: Their slenderness allows for slight flexing, which helps accommodate dynamic loads during leaf movement.
Spacing: Typically spaced 3–6 feet apart, depending on deck material and traffic demands.

Stringers, Warren truss design features, X-bracing, and the center of the bridge are shown in this telephoto looking north. The train deck is visible.

Substructure elements include precision-crafted gusset plates, stringers, and X-bracing.

stringers on a bascule bridge — Stringers, gusset plates, and bracing elements on the substructure.

Sidewalk cantilevers and X-bracing at the north leaf bridge pit and along the clear span, as viewed from the Riverwalk. Fenders on either side of the abutment prevent collisions with the bridge structure.

Stringers, X-bracing, lateral bracing, and sidewalk cantilevers are shown in this view from the Riverwalk.

IV E. North Train Deck Approach Span Engineering Features

These sections of the north train deck approach span that link the Brown Line station at the Merchandise Mart to the clear span’s train deck are particularly technically complex.

X-bracing, batten plates, and gusset plates along the north leaf train deck approach span. In these shorter members, the batten plates offer discrete stiffening. The plates help distribute axial loads evenly across built-up sections.

Batten plates (above and just right of center) along curved sections of the train deck approach span supports, along with X-bracing, stringers, and the Brown Line station at the right. Batten plates are visible in the vertical posts and diagonals of the Warren truss, particularly near the counterweight arms and approach spans.

While primarily functional, batten plates contribute to the visual rhythm of the bridge’s steel work, anchoring the geometry of the truss with regular intervals. Their presence reinforces the bridge’s identity as a machine aesthetic civic structure, where form follows function but also narrates Chicago’s industrial legacy.

Batten plates and X-bracing along the train deck approach span at the north leaf and Brown Line station.

Batten plates, gusset plates, and X-bracing between the train deck approach span and the clear span at the north leaf. Their use reflects early 20th-century engineering practices—favoring **riveted construction** and modular assembly for ease of fabrication and erection.

The southbound portal from across the street, facing east.

Looking southbound under the north leaf train deck approach span

South leaf portal, with bracing and plates for the gear rack and train deck. Train deck approach span is to the left in this southwest- facing view. Top chord connections are also shown near the upper right corner.

V. Bridge Lifts: Geometry and Civil Engineering in Motion.

East elevation sidewalk looking northbound as crews get ready for a bridge lift.

Movable bridges experience dynamic loads during opening/closing.
Bracing mitigates oscillations and harmonic vibrations, particularly in long-span or heavily trafficked structures.

Both leaves begin to rise. This north-facing view shows many features of the clear span: sidewalk with decorative approach railing, barricade arm lowered, intermediate bracing, gusset plates, and some of the thousands of rivets that keep the precision plates in place. Top and bottom chord bracing is also shown.

Both leaves are raised in this north-facing view of the bridge, as boats prepare to pass through. Shown are the superstructure’s Warren truss, elements of the substructure, south bridge house, and north abutments. Cylindrical yellow fenders help reduce collisions with the bridge structure.

Both leaves raised. Substructure bracing and gusset plates of the south leaf are in the foreground. North leaf substructure elements include abutments, bridge house foundation, stringers, and bridge pit.

Wells Street Bridge south leaf raised — The bridge’s south leaf is raised to allow passage of watercraft. To the left is part of the train deck approach span. To the right is the bell on the south bridge tender’s house. Intermediate bracing is noted along the inner portion of the leaf.

VI. Civic Symbolism and Decorative Details

Carnegie USA steel company mark. The company’s role during the 1922 construction was supplying raw steel, likely rolled beams or plates. While the Fort Pitt Bridge Company is documented as the fabricator of the steel used in the superstructure, Fort Pitt was known to source steel from major producers like Carnegie Steel. The company later became part of U. S. Steel.

Nucor-Yamato Steel (NYS USA) brand mark on a diagonal beam. NYS was a source of structural steel components for the rebuilding of the bridge. While they weren’t the fabricator or contractor directly assembling the bridge, their wide-flange beams and H-pile sections—produced at their Mississippi County, Arkansas facility—were likely part of the raw material stream that enabled the off-site fabrication of the new river arms and structural members. Material Characteristics: NYS steel is known for its high strength-to-weight ratio and consistent quality, which are critical for movable structures like bascule bridges that endure dynamic loads and frequent motion.

View of the south train deck approach span from the Riverwalk that parallels Upper Wacker Drive. The masonry is along the abutment and wing wall, concealing steps that connect Wacker Drive to the Riverwalk, and the decorative balustrade lines the approach to the bridge sidewalk.

Decorative sidewalk approach railing, with approach balustrade in the background

1922 bridge dedication plaque displaying names of officials and companies involved in the bridge’s construction. These plaques are on the bridge tender’s houses.

Conclusion

Chicago’s history of the use of movable bridges (swing, rolling lift, vertical lift, and trunnion styles) began from around the founding of the town in 1834. The lay of the Chicago River’s narrow depths to around 21 feet with some deeper pockets, and winding widths along its branches, of around 125 to over 200 feet made bridge engineering a true civic challenge.

The building of the classic trunnion bascule bridges as we view them today began around 1900, as the city’s population reached 1 million. The trunnion bascule design allowed for the large axles (the trunnions) and the massive counterweights that balance the bridge leaves to be hidden in the riverbank.

Changes in the river’s course, dredging, and advances in engineering help maintain the river as a vital waterway for shipping and industry. Wells Street Bridge is an essential link for daily commuters.

The city’s collection of bascule bridges is one of the best in the world, and with sensitive maintenance such as that being done on spans along all the river’s branches, these spans will continue to serve travelers and commerce for decades to come.

Sidewalk cantilever bracing and decorative clear span railing from the Riverwalk.

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