The complex Arroyo Bridge project in a Los Angeles canyon combined the design skills of students at the University of Southern California (USC) School of Architecture and a precision semi-robotic process to decrease construction waste.
The idea for the 70-foot Arroyo Bridge began as an assignment for thirteen students to design a pedestrian bridge using parametric design tools in the school’s design-build studio. The bridge had to be site-specific, with access to “treetop views.” Four different and “fascinating” concepts evolved, and the group selected the one with the aesthetics of structure that interested them the most: an elaborate web of steel tubing, with a layered structure inspired by tree branches.
Although originally intended as a design challenge, along the way the Architect of Record, David C. Martin, envisioned the project as actually being built. However, its geometric complexity and asymmetry ended up being too difficult to build with traditional manual manufacturing methods.
The main issues were the need for a framework (formwork) and fixturing of structural members to hold them in place for proper welding. Both the location and design contributed to requiring impractical amounts of fixturing for construction.
The group reached out to Autodesk Research Robotics Lab and the Martin Architecture and Design Workshop (MADWORKSHOP) to investigate how the project could be accomplished. Getting creative with ways to place and hold parts without using formwork for fixturing, the workgroup came up with the idea to use a massive robotic arm for a “collaborative robotics” effort. Collaborative robotics combines the precision of robotics with human creativity and adaptability.
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The work coupled human master welders and an industrial robotic arm, which did the heavy lifting and held the parts in the precise position required for welding – within one millimeter of tolerance. Formwork, which can be imprecise with an engineering tolerance of six millimeters, was not needed. Formwork can be a significant portion of the total project cost, and it is typically dismantled and discarded after a job. Eliminating the need for it drastically reduced the amount of materials waste and expense.
During construction, 500 discrete parts made of steel tube and plate steel were welded offsite, prepainted, then transported to the bridge site in 30 sections and connected together. Precision laser and waterjet precutting also kept scrap steel to a minimum during fabrication. A 2021 article in Dezeen magazine reported the six-year project generated less than 1,100 pounds of construction waste, all of which was recycled. Traditional methods could have generated up to 6,000 pounds of waste from the project. Completing the Arroyo Bridge project with traditional fixtures and fabrication methods would have been more labor intensive, expensive and wasteful and less accurate. Rather than replacing workers with automation, this real-world collaborative robotics project combined the two working together to accomplish the same task.
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