Reinventing the Suspension Bridgefor an Urban Crossing

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In February 2020, the 16 Tech Community Corporation announced plans for a new gateway bridge over Fall Creek in Indianapolis, that could link the 16 Tech Innovation District to the Indiana University-Purdue University Indianapolis medical corridor and function as a civic landmark. schlaich bergermann partner (sbp), with Practice for Architecture and Urbanism (PAU), Martha Schwartz Partners, Shrewsberry & Associates, and several local partners, was awarded the project and went on to develop a first-of-its-kind structure in the United States: flat steel plate ribbons in place of conventional suspension cables, carried over fan-shaped masts. The bridge opened in April 2025 and received the NCSEA Structural Engineering Excellence Award in the Bridge and Transportation category that same year.

The project brief called for four traffic lanes , but the design team saw a possibility to reduce that to two lanes across the structure. Traffic studies confirmed the two lanes would handle projected volumes comfortably. The recovered width was reallocated for pedestrians and cyclists to build a structure that had a more significant value for the community.

The resulting 65-foot-wide deck consists of two traffic lanes, a dedicated bicycle lane, and pedestrian sidewalks that cantilever 11 feet on each side. On the east side, the sidewalk expands to 18 feet at midspan to create a central gathering space and overlook above the creek. This aligned with what had surfaced through community engagement during the planning phase. Residents wanted a crossing that felt safe for all modes of transportation and gave people a reason to stop and gather. They did not simply want a connection between two sides of the creek, but a destination.

This intent was applied to the details of the bridge design. sbp integrated the lighting design as part of the structure from the beginning and embedded LED fixtures within the pedestrian handrails and continuous channels along the steel ribbons. The lights traced the wave form of the bridge at night, further establishing it as an urban landmark after dark. Anti-climb protection on top of the ribbon plates was similarly integrated into the smooth aesthetic of the bridge, providing safety without breaking the visual line of the structure.

The defining feature of the 16 Tech Bridge is the replacement of conventional suspension cables with flat steel plates. The ribbon plates follow a wave-like profile along the length of the bridge, giving the structure the slenderness and efficiency of a suspension system while remaining appropriate for an urban crossing of this scale.

The bridge spans 342 feet across Fall Creek, with a 152-feet central span flanked by two 95-feet side spans. Four concrete piers, arranged in two pairs, support the three-span structure. At each pier, five rectangular hollow sections, each 24 inches deep by 8 inches wide, form a mast. The sections fan outward and rise approximately 13 feet above the deck, allowing the ribbon to transition smoothly over the support rather than bending sharply. The masts also extend below the deck and connect to the concrete piers at the 100-year flood elevation, carrying the architectural expression of the superstructure into the substructure.

The ribbon plate, 20 inches wide and 2 inches thick, support the two longitudinal plate girders through vertical hanger plates. The girders are 42 inches deep and 24 inches wide, with web plate thicknesses varying from 0.75 to 1.75 inches and flange thicknesses from 1.125 to 2.5 inches, according to demand. Transverse cross beams at 9.5 feet intervals span 42 feet between the two girder lines and support the composite concrete deck, which is 8 inches thick, including a sacrificial wearing surface.

Traffic and pedestrian loads transfer from the deck into the girders and then into the ribbon plates, which act primarily in tension. The vertical forces are transferred through the fan-shaped masts into the piers and foundations. The horizontal component of the ribbon tension is balanced by compression in the girders, creating a self-anchored structure that limits horizontal reactions at the foundations.

The ribbon profile was designed through a numerical form finding process that minimizes bending moments under dead load, leaving the structure to act predominantly in axial tension and compression. This utilizes cross sections more efficiently than a system governed by bending.

Using parametric models in Grasshopper, Rhino, and SOFiSTiK, the design team defined the boundary conditions and load distribution along the span. The deck weight was represented as concentrated vertical loads at each cross beam. Static equilibrium at each hanger-to-ribbon connection then determined the ribbon angle, producing a funicular polygonal profile.

Global behavior was evaluated using a 3D finite element model from SOFiSTiK with line and shell elements for the superstructure and substructure, with load combinations following AASHTO LRFD requirements.

For more complex connection regions, including the mast-to-girder interface and the ribbon-to-girder transition, refined shell-element submodels were developed to study local stress distributions and confirm the detailing of welds and plate geometries.

The bridge is fully integral, with the girders connected directly into the abutments and piers without bearings or expansion joints. This design simplifies long-term maintenance, but it also shifts thermal expansion and contraction, creep, shrinkage, braking forces, and other longitudinal effects as loads on the substructure. To capture that behavior realistically, the design team modeled the driven piles directly in the finite element model, including lateral springs calibrated from site boring data.

The foundation system uses driven H-piles to provide reliable support through the variable sands, gravels, and silty soils typical of the Fall Creek floodplain. The connections between the encased girder ends and the reinforced concrete substructure were checked using strut-and-tie models to confirm that concentrated forces from the superstructure could be transferred safely into the abutments and piers.

The slender ribbon and hanger plates were assessed for wind-induced effects using AASHTO provisions. The fundamental periods were confirmed below 1 second, outside the range where resonance with wind excitation was a concern.

With high tension forces in the ribbon and hanger plates, fatigue and fracture behavior were an important aspect of the detailing. Hanger and ribbon connections were detailed for the governing stress ranges, with particular attention to welded terminations, bolted splice geometry, and plate transitions avoiding sharp corners and stress concentrations. Material toughness requirements supported a fracture-safe design approach appropriate for primary tension elements.

Although the ribbons carry significant tension, the continuous longitudinal girders and repeated hanger arrangement provide alternate load paths in the event of a localized connection issue, improving the bridge’s ability to redistribute forces.

With a natural frequency of 3.55 Hz, the sidewalk system falls into a range where human-induced vibration warrant careful evaluation. Using the HIVOSS Design of Footbridges guidelines, the team evaluated two scenarios: an inauguration crowd with a density of one person per square meter and daily commuter use at 0.2 persons per square meter. A dynamic time history analysis showed a maximum vertical acceleration of 2.1 meters/second squared for the crowd scenario, placing the response in Comfort Class 3. Comfort Class 3 is acceptable for a large public event where some movement is expected. Under daily use, acceleration dropped to 0.4 meters/second squared, corresponding to Comfort Class 1, the highest comfort category. In practical terms, everyday users should experience little noticeable motion, while a dense event crowd may feel movement that remains within acceptable limits.

The site sits within the Fall Creek floodplain and ties into an existing levee. Both permanent and temporary works had to respect hydraulic performance and flood protection requirements. The wooded creek corridor also provides urban habitat for bald eagles and other animal species, which made it a priority to limit disturbance. The fabrication and erection strategy was shaped around these conditions.

To reduce the disruptions to the wooded creek corridor, minimize traffic disruptions, and increase cost efficiency, the steel elements were prefabricated by Cimolai in Italy. The bridge was divided into segments sized to fit standard 40-foot containers, with bolted connections used in most locations to simplify field installation. The girders were split into 10 bolted segments, and the masts and hangers were bolted to the girders at locations that would later be embedded in the concrete deck and hidden from view. The exposed ribbon plate splices at the crest of each wave were field-welded to achieve a seamless appearance, while bolted ribbon-to-girder splices were concealed beneath the anti-climb protection. This allowed the completed bridge to read as a continuous ribbon, with the practical logic of bolted modular construction hidden.

Achieving the correct final geometry under permanent loads was critical to ensure the bridge behaves as designed. Specifically, if the ribbon plates did not engage the girders as intended, the girders would carry more load in bending rather than transferring load into the ribbons axially, undermining the structural logic of the system. To guard against this, the full ribbon plate, girder, and hanger assembly for each of the four waves was first trial-assembled in the fabrication shop. Bolt holes for the splices were drilled during trial assembly after the fit-up and survey confirming the geometry.

Camber was applied to the girders to meet target road grades after dead-load deflections. Rather than fabricating curved girder segments, the team introduced camber at the splices, which simplified shop work while achieving the required final geometry with only small deviations from the ideal profile.

Once the segments arrived on site, they were partially pre-assembled on the ground before being lifted into position with crawler cranes. The main span required temporary shoring, with the towers placed outside the main creek channel to avoid disrupting water flow.

At the southern approach, where the bridge alignment crosses the levee, the design incorporated a removable flood-log barrier. This detail maintains a continuous line of flood protection that can be deployed in advance of high-water events.

Embodied carbon has become an increasingly important metric for evaluating infrastructure performance. For the 16 Tech Bridge, a lifecycle calculation covering modules A1 through A5, from material production through construction, yielded a total embodied carbon of approximately 840 kg CO₂e/m² of functional area, including the superstructure, substructure, and foundations. For context, studies referenced in the SCORBS rating framework indicate that conventional steel bridges often range between 1,000 and 4,000 kg CO₂e/m², with an average around 2,570 kg CO₂e/m². Internal benchmarking across completed sbp footbridge projects has established a range of 500 to 1,800 kg CO₂e/m², with mid-span bridges such as the 16 Tech Bridge generally falling at the lower end of the range. Even on that basis, the bridge sits below the conventional steel-bridge average. Under the SCORBS framework, which normalizes carbon intensity by span and deck width, the bridge achieves an A rating.

The rating reinforces one of the project’s central lessons: architecturally expressive infrastructure and environmental efficiency do not need to be in conflict. The result reflects the material efficiency of the plate ribbon concept. Through careful detailing and fabrication, the bridge provides a more efficient primary structure than a conventional girder bridge of comparable span, while also delivering a slender, expressive appearance.

Focus on material efficiency extended to the smaller details as well. The benches in the midspan gathering space were fabricated at the local Machyne Makerspace from timber reclaimed from trees cleared during construction, returning something of the site to the people who helped shape the project.

The 16 Tech Bridge represents structural efficiency and architectural expression operating together rather than as competing priorities. By adapting classical suspension principles to the specific demands of an urban crossing, the design replaces conventional cables with flat steel plate ribbons, producing a structure with clear load paths, efficient use of material, and a distinctive identity. The design goals were coherent through the integral detailing, precise fabrication, and low embodied carbon result. The bridge expands access for pedestrians and cyclists while delivering a landmark for the 16 Tech Innovation District and the wider city of Indianapolis. ■

Matthias Peltz, PE, is a Senior Project Manager and Structural Engineer at sbp. He served as Project Manager and lead structural engineer for the 16 Tech Innovation District Bridge.

Michael Stein PE, is the managing director of sbp’s New York City and Los Angeles offices and a member of the board.