Self-supporting lamellae: Shape variation methods for the 3D concrete printing of large overhang structures

3D Concrete Printing (3DCP) is considered a solution to confront both labor shortages and material waste in the construction industry. However, to realize non-standard, large-scale buildings, substantial amounts of supporting material and manual assembly are still required to print structures with significant overhangs, including the inclined structure and the cantilever structure. In response, the study draws inspiration from mushroom lamellae and proposes a geometry-based approach to adjusting the large-overhang shape into a self-supported one. This approach imitates lamella morphology by creating folds on the given geometry based on constraints established through empirical studies, thereby reducing overhangs and improving printability. Specifically, the proposed approach includes two shape variation methods. The first method generates lamellae perpendicular to the inclined shape, thereby providing lateral support to the filament. The second method creates lamellae under the cantilever, facilitating a seamless horizontal-to-vertical transition. The effectiveness of these methods is demonstrated through the generation and printing of four column capital samples. Upon evaluating the overhang mechanisms of these geometries, an approachable optimization method is also presented to further minimize the amplitude of lamellae while maintaining self-supporting ability. Compared with control groups that focus on either maximizing printability or minimizing material usage, the optimal result for the inclined structure prototype showcases an over 75 % overhang reduction on the critical layer with just about 15 % use of additional material. As for the cantilever prototype, an over 75 % overhang reduction is achieved on the critical layer with about 35 % additional material usage. Various large-scale structure examples are presented at the end of the research, illustrating the applicability and scalability of the lamella-inspired method in a wider range of building types.