A 3D-printed steel pedestrian bridge wins the 2021 Forge Prize

Balboa Brawn

A 3D-printed steel pedestrian bridge wins the 2021 Forge Prize

The winning design of the 2021 Forge Prize is a pedestrian bridge that marries steel innovation and public space in San Diego’s Balboa Park.(Courtesy Forge Prize/AISC)

A singular 3D-printed steel pedestrian bridge spanning Florida Canyon in San Diego’s Balboa Park has been named as the winner 2021 Forge Prize, a conceptual design competition from the Chicago-based American Institute of Steel Construction (AISC), now in its fourth cycle.

With a striking organic form, ingenious (compulsory) use of steel as a main structural component, and the clever integration of public space including a pulse-quickening hammock/aperture situation, the Florida Canyon pedestrian bridge is the creation of Hunter Ruthrauff, a senior design associate within the Architecture and Visualization Group at the San Diego office of global engineering services firm T.Y. Lin International. Ruthrauff is also a founding member of the firm’s innovation department and the head of its Digi-Fab Lab, which focuses on 3D printing and CNC routing.

A graduate of Cal Poly Pomona and the University of Washington, where he received his Master of Architecture in Design Computation, Ruthrauff has led the design of numerous bridges for T.Y. Lin including the 4th Crossing at the Panama Canal, the Avalon Gateway Bridge in Los Angeles, and the Fremont Innovation District overcrossing in Fremont, California. Ruthrauff is also cofounder of M-Form, a San Diego-based digital fabrication company specializing in the production of curved architectural panels using patented robotic mold technology. As noted in the prize announcement, Ruthrauff “chose 3D-printed steel because it offers better tensile strength than 3D-printed concrete and lessens the complexity of the design process” in his design submission.

rendering of a park atop a pedestrian bridge
Not for the faint of heart: An “observation hammock” high above Florida Canyon. (Courtesy Forge Prize/AISC)
aerial rendering of a pedestrian bridge
Laced with hiking trails, Florida Canyon is located in the northeastern section of Balboa Park. Ruthrauff’s design nods to the local flora as well as the Spanish-inspired architecture of the area. (Courtesy Forge Prize/AISC)

This is the second consecutive year that a pedestrian bridge has won the Forge Prize. In 2020, the top honors went to a theoretical footbridge and elevated park for Manhattan conceived by Rosannah Harding and Matthew Ostrow of HardingOstrow.

This year’s finalists also include a civic mixed-use plaza for Richmond, Virginia that incorporates folding steel plates designed by Mert Kansu and Yimeng Teng of VMDO Architects and Signal Park, a “cluster of urban villages” envisioned for San Jose that features a shading, rainwater-collecting steel scaffolding structure. Jieun Yang of Habitat Workshop designed the latter concept.

As the winner, Ruthrauff will receive a cash prize of $10,000. Following the design presentations given by all three 2021 Forge Prize finalists on March 31, Ruthrauff will give an encore presentation of his winning design on April 12 at NASCC: The Virtual Steel Conference.

While the AISC launched the Forge Prize in search of envelope-pushing conceptual designs that aren’t necessarily likely to be realized, the competition jury viewed Ruthrauff’s submission, which offers a noted departure from 3D-printed concrete construction, as more than just a radically quixotic idea unbound from any real-world design and engineering considerations.

detail view of 3d-printed steel bridge
While steel-centric designs entered into the Forge Prize are purely theoretical, the competition judges saw real-world potential in Hunter Ruthrauff’s winning submission. (Courtesy Forge Prize/AISC)

“I don’t think any of us have a doubt in our mind that it’s going to come together and be a catalyst for the rest of us across the country,” said competition juror Pascale Sablan, an associate at Adjaye Associates Architects and founder of Beyond the Built Environment, of the Balboa Park pedestrian bridge. “[Ruthrauff] really convinced us that [he] can actually help solve some of the infrastructure issues that are plaguing our nation.”

In addition to Sablan, the 2021 Forge Prize jury was comprised of Dallas-based architect and blogger Bob Borson and Robert Cassidy, executive editor of Building Design+Construction.