Robotic Fabrication Of Topology Optimized Concrete Components With Reusable Formwork

Yiyao Guo Zhejiang University
Yang Luo Zhejiang University
Sihan Wang Singapore University of Technology and Design
Ying Yi Tan Singapore University of Technology and Design
Kenneth Tracy Singapore University of Technology and Design

In this paper, we present a design to fabrication process of full-scale topology optimized concrete components by envisioning 3D printing clay as a temporary mold with concrete to be cast in simultaneously. Such an approach takes advantage of additive manufacturing that can fabricate freeform concrete components with complex geometries such as branches, cantilevers, and overhangs. By casting concrete within the mold simultaneously during the printing process, each portion of cast concrete has sufficient time to set, thus, solidifies and exerts less lateral pressure on the clay mold. Therefore, less mold material is required to sustain the concrete pressure, which increases fabrication efficiency. Furthermore, it facilitates the removal and recycling of mold material by the air drying, shrinking, and cracking nature of clay. This investigation is built upon a case study that focuses on supporting trees in typhoon weather in the urban context. The stem of a tree tends to break in strong winds when the wind load exceeds its maximum capacity. In this scenario, we propose to brace the trees with permanent support structures made of concrete which have better weather resistance compared to other temporary supports made of timber or steel. Meanwhile, an integrated function that sits people during non-typhoon seasons is also included. Therefore, the support structure is designed as benches axially arrayed around trees to secure the stem, which considers the potential wind load from all directions in typhoons. The design of these structural components is generated by topology optimization according to two types of loading conditions, the wind load in typhoons, and the sitting load in non-typhoon periods. Once the geometry is designated, it is analyzed with our fabrication module to arrange the fabrication process, namely, the planning of printing and casting sequences based on calculations of printing speed and concrete setting time, with considerations of its overall workability, material properties, and fabrication efficiency. In the fabrication section, we first introduce our fabrication workcell setup including a customized clay printing end effector driven by an industrial robotic arm, a material preparation sector, and a fast-reloading workflow enabling less interval material loading time among printings. This is followed by the introduction of the fabrication process with an elaboration of material choice, fabrication schedules, and team cooperation. Subsequently, we demonstrate the ease of the demolding process of clay. In the end, we discuss the outcomes on the feasibilities and challenges of this approach in fabricating complex freeform concrete components on a large scale. The discussion reviews the fabrication process and the post-process respectively, with focuses on the workability of producing branches with cantilevers and overhangs as well as the remaining challenges in demolding. Last, we propose our future work of a fully automated robotic fabrication system developed upon this approach.

Keywords: Robotic Fabrication, Topology Optimization, Freeform Concrete, Reusable Formwork

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