By Grace Melcher
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Frequently in the construction industry, speed, affordability, and scalability come at the cost of beauty and functionality. In March 2023, construction technology company ICON partnered with the Long Center for the Performing Arts, Bjarke Ingels Group (BIG), and Liz Lambert to construct the Cosmic Pavilion in Austin, Texas, the first ever 3D-printed performance stage.
One of the major benefits of 3D-printing technology is speed. Traditional construction methods often involve time-consuming design and sourcing, but with 3D-printing technology, the construction process can be accelerated. This not only saves time but also can control costs associated with labor and materials. Additionally, the reduction in material waste is a significant advantage in an industry that is increasingly focused on sustainability.
Customizability is another major benefit of 3D-printing technology. The ability to create complex and intricate designs opens up worlds of possibilities for architects and designers. Structures can be tailored to meet specific requirements and aesthetic preferences, allowing for greater creativity and flexibility in the construction process without altering the cost.
One implementation of construction 3D printing is utilizing a vertically integrated approach. ICON utilizes this approach and combines robotics (both design and manufacturing), software, material science, and architecture to provide a seamless workflow and precise structural execution.
ICON’s material deposition robot, called The Vulcan, was utilized to print the Cosmic Pavilion. This 15-foot x 46-foot x 130-foot robot operates in the cartesian plane and travels on Vulcan Y-rails, allowing for precise material deposition. The proprietary material used in the printing process is called Lavacrete. Lavacrete is a 2-3.5 ksi cementitious grout material that is a specific combination of fine aggregate and cement. This material is delivered from Magma, which is the Lavacrete handling and batching system, equipped with a mixer and pump delivery mechanism.
Cosmic Pavilion Design
Designed in partnership with BIG, the Cosmic Pavilion draws inspiration from the architectural design themes planned within an upcoming expansion of the El Cosmico development in Marfa, Texas. The Pavilion is an undulating curved surface that acts as a landmark, performance stage, and gathering space for culture and community in Austin.
One of the most striking aspects of the Cosmic Pavilion is its freeform geometry. The structure features multiple layers of circles, and leaning, out-of-plane walls, creating a visually captivating design that would be challenging and expensive to achieve using traditional construction methods. Laminar deposition of material naturally creates striations in the print, which gives the structure a unique, rammed-earth aesthetic.
Printing was the primary function that enabled the architectural expression of the Cosmic Pavilion. From the first layer to the last, the print only took two weeks, while the design and engineering for permitting required three months to prepare. In addition, reliance on digital and automated construction methods guided creative engineering solutions. The digital twin, or print path, used to direct Vulcan where to deposit material enabled geometrically precise rebar fabrication. It also enabled easy transition to other analytical tools that further assisted the structural design. The printing method took advantage of the ability to cantilever bead-to-bead in real time, which bypassed the use of formwork, thus reducing costs, time, and eliminating waste.
Challenges
There were several challenges in printing the undulating, lofted geometry of the pavilion. The real-time challenge of cantilevering bead-to-bead required a collection of approaches to overcome.
One of the primary challenges of cementitious extrusion is this limitation of the cantilever angle. Unlike small-scale polymer additive manufacturing, cementitious extrusion lacks tension capacity across extruded bonds. This limitation becomes a significant hurdle when attempting to realize lofted designs without additional support systems such as formwork.
To understand the solution space for the pavilion, existing literature on classic masonry solutions was used. The internal angle of friction and cohesion of the material is what primarily determines the maximum cantilevering angle in any 3D-printed cementitious object. Typically, a common angle limitation is around 25 degrees from vertical. Exceeding this angle can lead to elastic buckling, plastic collapse, and structural instability. In order to achieve the pavilion design without expensive and time-consuming formwork, a highly specific solution was formulated to mitigate common cantilevering failure modes.
Mortars’ yield stress is nonzero even in fresh and green states. Lavacrete in the fresh state has enough yield strength to support itself and resist plastic collapse in the vertical condition. However, the cantilever condition induces more stress on the material than the standard vertical condition. To overcome this for the pavilion, rheological properties and an operations strategy that relied on precise and coordinated timing was executed. This allowed the material to gain more yield strength, and thus the Lavacrete’s internal angle of friction was decreased prior to deposition. Manipulating these material properties allowed the maximum cantilever angle to be improved and prevented failure by plastic collapse.
Additionally, a reinforcement strategy using steel wire was employed. The tension on the bead-to-bead interface and the global out-of-plane shear induced by cantilevering created a higher risk of elastic buckling. Wire reinforcement (9 gauge) was placed between beads in the longitudinal direction every other layer in areas where the structure exceeded the 25-degree from vertical failure limit. This reinforced the shear during the green phase of the material and supported the structure during the curing process. By increasing the individual beads’ shear strength, ICON was able to achieve a cantilever angle of 35 degrees from vertical, without altering the bead shape.
Another aspect that played a crucial role in overcoming the instability challenge was the build rate. Build rate is a significant factor in any 3D-printing project, especially when dealing with cantilevered designs. The length of the print path on a construction scale can be long, and this fact makes it easier to outrun the relationship between the additional layers’ self-weight and the material’s yield strength development.
Structure
The structural design of the Cosmic Pavilion combines elements of shell, wall, and beam design principles. The Cosmic Pavilion’s structure dynamically evolves both horizontally and vertically, ensuring high quality aesthetics and functionality. Key elements of the structural design include tilted cores, a stepped bond beam, and a robust reinforcement design.
The primary structural system is composed of cores connected to an upper stepped bond beam, and a lower planar bond beam. These vertical cores were created by voids included with the print path inside the hollow wall. After printing, vertical rebar was placed in these cores; the structural engineer then checked them for quality control. Finally, they were filled with Lavacrete using the Vulcan printer. These cores follow the profile of the pavilion, which undulates between -35 and 35 degrees from vertical. This caused the cores to be tilted in some areas.
Because the topline of the geometry comes down at the wing tips to embrace the earth, the upper bond beam is stepped in sections to brace this topline. The reinforcement consists of large rebars in the cores and upper and lower bond beams, with smaller rebars placed longitudinally between the beads during the printing process. The aforementioned digital twin enabled exact rebar shapes to be prefabricated and bent to match the printed geometry. In addition to the repeated rebar reinforcement, a reinforcement tie point is at the connection of the stage backdrop and the wing walls. This rebar tie ensured stability and structural continuity between the three walls. The pavilion also includes a halo ring around the top of the geometry to light and shade the stage for performances.
To validate the integrity of the pavilion, as with most primarily concrete based structures, a quality control and engineering validation plan was executed throughout the print. Material cylinders were taken and tested periodically to ensure that the structure reached the required compressive strength. A Finite Element Analysis (FEA) was also conducted on the pavilion design. This computational technique served multiple purposes, including:
Validation of Structural Mechanics: FEA was used to ensure that the structure met necessary safety standards.
Connection Point Investigation: A specific focus of the FEA model was an investigation of the connection point. This critical juncture required careful analysis to ensure it could withstand loads effectively.
Construction Sequencing Analysis: FEA played a crucial role in analyzing the construction sequencing of the pavilion. This ensured that stability was maintained during the construction process, minimizing the risk of structural issues during assembly.
FEA was conducted using both shell and solid elements, allowing for a comprehensive evaluation of the pavilion’s structural system. By comparing various approaches, a resilient structural design that could withstand the dynamic forces at play was created.
Conclusion
The 3D-printed pavilion stands as a symbol of the boundless possibilities that 3D printing technology offers the world of construction and architecture. It defies traditional constraints, marries aesthetics with functionality, and showcases the immense potential of advanced robotic construction practices.
The Cosmic Pavilion challenges the structural industry to push boundaries, embrace advanced methodologies, and reimagine what’s possible. It is a symbol of human ingenuity and the promise of an extraordinary construction future. ■
About the Author
Grace Melcher is the Arches, Domes, and Vaults program manager for ICON, which develops advanced construction technologies that advance humanity. Grace achieved her B.S. and M.Eng. degrees at MIT and specializes in shell structures. (gmelcher@iconbuild.com)