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Fab-Union / Archi-Union · PROFESSIONAL · DESIGN · FAB LAB

Christmas Tree & Concrete Printing

Developable-Surface Metalwork and Topology-Optimised 3DCP

Context
Fab-Union / Archi-Union — Professional Project
Role
Computational Design & Fabrication Development
Year
2021
Practice
DESIGN · FAB LAB
Location
Shanghai, China
Status
COMPLETED
Installed metal Christmas tree sculpture at night in the Archi-Union atrium

Overview

Two fabrication experiments installed at the Archi-Union atrium in 2021. The Christmas tree began as a SubD free-form study — a swept, lofted organic shape — then, for cost and schedule, was re-engineered into metal plate: every hyperboloid segment was optimised into a developable surface with the HARE plugin, refined through paper-film mock-ups and metal proofing into eight-sided polygons, batch-unfolded to cutting files and laser-cut for on-site assembly. The concrete-printing piece combined PolyFrame (a purely compressive funicular structure from 3D graphic statics) with Ameba topology optimisation; the final structure was segmented for printing, with steel plates inserted mid-print as positioning joints between units.

Ribbon-like render of the Christmas tree concept
Metal panel fabrication process
Robotic concrete 3D printed unit

Responsibilities

  • SubD form-finding and linear fitting of the Christmas-tree geometry
  • Metal-bending optimisation: developable-surface conversion and batch unfolding
  • Concrete-print segmentation strategy and positioning-joint detailing
  • Fabrication file output and on-site assembly coordination

Methodology

  • Free-form rationalisation: SubD modelling, sweep and loft through four reference lines, then developable-surface optimisation per segment
  • Segmentation for printability: force direction, maximum print height (<1500mm) and maximum printable inclination (≤45°) as the three governing factors; every segment keeps at least one horizontal surface
  • Mid-print pauses to manually place steel positioning plates — at least one per unit — which bond with the concrete into a single structural whole
  • Assembly sequence: three pillars welded to the foundation, second column sections, ground-assembled beams hoisted into place, then the three overhanging units; units cured at least 14 days before installation