Semi-Monocoque Plywood Structures *° 

DCS ° Shared Beds

DATE2019

LOCATIONHouston, TX and Lake Forest, IL

TYPEBuilding Science Research

FUNDINGRagdale Foundation 
Ragdale Ring Competition Winner 

PRIMARY INVESTIGATORDavid Costanza
Piergianna Mazzocca

OVERVIEWThis research outlines the development of a semi-monocoque plywood structural system used in Shared Beds, the winning installation of the 2019 Ragdale Ring competition. Designed as an interactive public space, the installation features three large-scale communal objects—two with 15-foot diameters and one with a 24-foot diameter—each constructed using a developable conic geometry that enables cold-forming plywood. The structural system employs a two-way waffle rib core made from laminated, staggered ¾-inch plywood ribs, sheathed with a stressed plywood skin to create an efficient, lightweight, and robust assembly. CNC fabrication techniques enabled precise joinery and minimized material waste, while avoiding costly double-sided milling. This digitally fabricated, all-plywood system—optimized for strength, ease of construction, and reduced cost—demonstrates how material research and digital manufacturing can inform scalable, interactive architectural structures that blur the boundaries between sculpture, furniture, and public space.

KEYWORDSDigital Manufacturing, Material Research, Design Build, Public Space, Interactive Installation

DESCRIPTIONThe installation comprises three interactive communal objects, constructed and installed on the grounds of the Ragdale Foundation. Two objects are defined by a circle with a 15 ft diameter. Resting on a tipping axis, these objects teeter back and forth depending on the movements of each occupant. The largest of the three objects, characterized by a circle with a 24 ft diameter, features an asymmetrical tipping axis that maintains a primary face in constant contact with the ground. While the smaller objects tilt according to their occupants’ motions, the largest object encourages occupants to reimagine their movements and performances on the upper oblique surface.
        The stage and smaller objects are designed using the same geometric, material, and structural principles. The semi-monocoque structure relies on stressed skins on either side of a compression core, unlike a full monocoque, where all forces are transferred solely through the skin. The design of this structural system began with deriving the overall geometry from a rotational cone, which is inherently limited to single curvature, allowing for a developable construction using plywood sheets. The conic geometry facilitates the use of sheet materials, such as plywood, to be cold-formed, functioning as an active bending structure to stress the structural skin.
        The internal frame consists of a two-way waffle plywood structure. Each rib forming the waffle comprises two layers of 3/4-inch plywood, arranged to negotiate the limits of the 4ft x 8ft plywood sheets by staggering the seams of the constituent parts. The two halves of the staggered plywood ribs were then laminated to create the structural ribs. The final ribs measured 1 ½” in width and ranged from 6ft to 24ft in length. The design of the laminated ribs facilitated the development of the waffle joint. Since the plywood was CNC cut on a 3-axis router, pockets could be embedded into each face to receive the open edge of the opposing rib. This detail was feasible due to the two-layer laminate and did not require flip-milling, which would have been prohibitively costly. Additionally, this innovation resisted the tendency for the ribs to fail due to rotational buckling by supporting the open edge of the perpendicular rib.
        The material and construction system efficiencies greatly simplify and streamline the budget and assembly. Utilizing the same 3/4-inch plywood for constructing the stage and the smaller objects optimizes material usage and reduces waste. Consequently, the material system is restricted to exclusively plywood, along with screw fasteners and urethane for waterproofing.


DCS