Synclastic Tensile Stone Canopy *° 

DCS ° Draped Stone

DATE2018

LOCATIONMadison, WI

TYPEMaterial & Fabrication Research

FUNDINGQuarra Stone Company

PRIMARY INVESTIGATORDavid Costanza

RESEARCH TEAMEkin Erar

OVERVIEWSynclastic Tensile Stone is an ongoing research project exploring the novel use of stone in tension through fiber reinforcement, resulting in a suspended marble canopy that challenges conventional stone construction. Collaborating with Quarra Stone and supported by multiple grants, the project investigates a sandwich panel system combining machined marble and laminated fiberglass. This composite structure internalizes tensile forces, allowing for a synclastic surface geometry traditionally incompatible with tensile systems. Inspired by the structural logic of the Expo ’98 Portuguese Pavilion and Dulles Airport, the canopy employs the weight of marble to tension internal fiberglass layers, achieving stability without external ballast or scaffolding. Simulations using Kangaroo 3D informed the catenary form and discretization into 36 machinable units, each designed for automated 5-axis CNC fabrication. Through iterative lamination and pull testing, a workflow was developed to optimize material performance, enabling the use of scrap marble otherwise unsuitable for structural applications. The result is a lightweight, visually delicate structure that demonstrates the untapped potential of fiber-reinforced stone to expand a traditionally brittle material's formal and structural capacities, with future implications for thinner, more sustainable, and substructure-free stone assemblies.

KEYWORDSStone, Material Waste, High-Performance Textile Composites, 5-Axis CNC Machining

DESCRIPTIONDraped Stone is a research project that uses stone in tension through fiber reinforcement, producing a hanging marble canopy. The research collaborates with stone fabricator Quarra Stone in Madison, Wisconsin, as part of a Research Fellowship. The project is still in development and is currently the subject of multiple grants to complete the pavilion. The project submission represents the work in progress, with all the research and development for a fiber-reinforced stone and an automated workflow for 5-Axis machining marble and laminating fiberglass to machined marble surfaces. 
        The canopy's form is derived from a hanging mesh simulation that produces a catenary draped surface. A traditional tensile structure is produced by stretching a surface between two boundary conditions with opposing curvature, resulting in an anticlastic surface. For this reason, tensile structures are formally very limiting in that they must always maintain an anticlastic surface curvature for stability. 
        The designed hanging canopy utilizes the weight of the stone to put the fiber-reinforcement into tension, allowing for a synclastic tensile structure. Typically, synclastic surface typologies are not possible with conventional tensile structures. The primary precedents for the project include—Siza Vieira, Álvaro. Expo’98 Portuguese National Pavilion. 1998, Lisbon, Portugal. and Saarinen, Eero. Dulles International Airport. 1958, Dulles, Virginia, U.S. These two projects represent a rare structural system that produces a catenary surface by utilizing the incredible spans of tensile structures without adhering to the geometric language and constraints of a tensile surface. In both projects, concrete is used as a sort of ballast to put the cables into tension, stabilizing the single negatively curved surface typology. Draped Stone builds on the structural logic of Expo ’98 and Dulles airport by introducing a synclastic doubly curved geometry and internalizing the tensile structure. Rather than steel cables with a concrete ballast, the project utilizes a sandwich panel of marble and fiberglass, where the fiberglass is continuous and used to transfer the tensile loads. The marble is used for its weight to put the fiberglass into tension and to stabilize the otherwise unstable surface typology. 
        Kangaroo 3D was used to simulate the catenary surface and to discretize the surface into bands of flat face units. To manufacture the units using the 5-Axis CNC, one of the faces of the surface had to remain flat on the bed of the machine. For this reason, the canopy was designed with a smooth, continuous interior surface and a rougher exterior surface made up of the various flat faces of the units. The flat face simulations allowed for optimizing the material thickness and the manufacturing process. After many tests and iterations, the simulated mesh was discretized into three closed bands, resulting in 36 discrete units. For the canopy to be constructed without scaffolding or falsework, each band needed to close in on itself, positioning the blocks in the correct location. 
        Each of the units is conceived of as a sandwich panel. The fiberglass reinforcement is in the middle of two doubly curved, machined marble blanks. The machined surface is extracted from the hanging mesh simulation and represents the pure catenary surface in the middle of the canopy. Each unit is connected with small steel tabs through the middle layer of fiberglass, keeping the tension at the center of the blocks, never on the face of the marble. Pull tests were used to develop the connection detail between the units. The steel tabs are made of 1/8” steel plate and are located between the two layers of fiberglass mat. 
        The process for constructing the sandwich panels consists of first preparing the machined stone surface, then laminating each face independently. A three-way fiberglass mat was used as the reinforcement. The fiberglass mat takes the place of a more involved built-up fiberglass isotropic assembly of 5-13 layers of plain-weave fiberglass. The entire assembly is vacuum bagged at -29 in.HG will compress the assembly and remove the access resin. The two halves were laminated separately to produce small pockets for the steel connecting tabs. Finally, Part A and Part B are then epoxied together. 
        The development of the lamination workflow evolved over many tests and iterations. The iterations consisted of varying amounts of fiberglass, different types of laminating epoxies, and different stones. The sample magazines were then load tested using a three-point test to analyse the fiberglass reinforcement's role in strengthening the stone. 
        Because the marble was reinforced, the canopy was constructed entirely from scrap marble found at Quarra. Many marble blocks that could not otherwise be used due to fracture lines and other natural deficiencies can now be reinforced with fiberglass and employed in a structural capacity. The reinforced hanging canopy, which reads as precise, delicate, and thin, made from white marble and digitally produced, is held up by a dark grey granite wall, which is massive and rough, exposing the texture derived from the quarrying process.
        The potential for fiber-reinforced stone, operating in tension, is significant. Typically, stone is used in smaller blocks that tie back to steel hat channels as façade material. Stone, a brittle material, has a thickness-to-span ratio that limits its typical use. To span further, the stone must also increase in thickness, which restricts its application due to the added weight. New techniques for laminating stone to plastic or aluminum backers have allowed for a more predictable and stable material. However, it still has size limitations and relies on a steel substructure for support. Looking ahead, the ability to transfer stone between floors presents several advantages over existing systems. Firstly, the stone remains visible on both sides of the unit rather than being treated as a backer. This is particularly valuable for the stone used as a screen before a curtain wall system. Secondly, being fiber-reinforced means that the stone cladding would not necessitate an elaborate steel substructure. Finally, using stone in tension permits a thinner stone surface while reducing material consumption.


REFERENCES
[1]    Siza Vieira, Álvaro. Expo’98 Portuguese National Pavilion. 1998, Lisbon, Portugal.

[2]    Saarinen, Eero. Dulles International Airport. 1958, Dulles, Virginia, U.S.

[3]    Faircloth, Billie. Plastics now: on architecture’s relationship to a continuously emerging material. London New York: Routledge, Taylor & Francis Group, 2015. Print.

[4]    Bell, Michael, and Craig Buckley. Permanent change: plastics in architecture and engineering. New York, New York: Princeton Architectural Press, 2014. Print.

[5]    Campbell, F. C. Manufacturing processes for advanced composites. New York: Elsevier, 2004. Print.

DCS