Architecturedesign
Precarious Stand
Thesis work in University of Michigan
Team: Xiaojie Cao
Instructor: Tsz Yan Ng, Wes McGee
Taubman College Thesis Honors Exhibition
Published: ACADIA 2019 Ubiquity & Autonomy , Precarious Stand.
Precarious Stand explores the design and fabrication of a self-supporting dry-fit cantilever masonry system by controlling the centroids of the units’ vertical compressive force. Concrete Masonry Units (CMU) are basic construction blocks that are ubiquitously used in our everyday world. This project challenges the singular nature of typical CMUs in its form and mode of assembly, by offering complex geometries as a fully assembled system, as well as customization for formwork production enabled by digital technology. Exploring the use of robotic hotwire cutting and ruled geometries, EPS foam molds were cut to cast the glass fiber reinforced concrete (GFRC) units.
Controlling the centroid of each column of stacked units so that cantilevering could be achieved as the wall progressively bends.
Centroid aligned for the each wall section.
Connection details.
Exploded axon diagram of two typical formwork for seat area and wall area.
Matrix diagram of all molds used for the casting.
EPS foam formwork parts for entire assembly.
Final prototype at half-scale.
Using Grasshopper plug-in for Rhino, the centroid balance, as in the force distribution of the masonry units, could be predetermined as part of the design process. Drawing from the project Robotic Fabrication of Stone Assembly Details by Ariza, Clifford, Durham, McGee, Mueller, and Sutherland where physics analysis is used to determine both the global and local equilibrium of a masonry compression assembly system, this project challenges concrete masonry units to assemble without the use of mortar but cantilever through the shaping of the units’ centroid. Early prototyping explored the prospect and extent of the cantilever as sectional slices. By using its own self-weight, tapered shaping to the units, and choreographed sequence of assembly, the masonry system could be stacked without scaffolding or falsework during construction. To enable quick deployment, the design exploration also focused on masonry construction whereby mortar is not necessary, using male/female dry-fit jointing system and dowel connections for vertical racking. Connection tolerances were calibrated into the final design after a series of prototype testing to both deals with the hotwire cutting process and shrinkage from the cured concrete. The dry-fitting offers the opportunity to construct the cantilevered system quickly and could also be deconstructed without damage to the units. This suggests that the assembly system could be temporary, to be moved and rebuilt in another location.
The EPS foam formworks for concrete casting were produced using robotic hotwire cutting processes. Working with ruled surface geometries and limitations guided by the hotwire cutting process, the unique molds for the assembly were manufactured quickly and efficiently in terms of material use. (All the mold pieces were cut in two days.) Each mold was prepared with an epoxy coating, waxed, and release sprayed before casting. The molds could be reused as necessary.
The final design of an enclosure explores experiential effects when people are gathered within. The semi-circular sloped design welcomes and embraces individuals in the structure. The final half-scale proof-of-concept aims to highlight the diverse and complex formal geometries that this molding process offers, especially when the system assembled will produce complex surface geometries with stable cantilevering. Precarious Stand provides temporary shelter for sitting and sun-shading.
