Design optimization and assessment of stay-in-place 3D printed concrete formwork for slabs

Extrusion-based 3D printing has recently expanded into fabricating concrete structures with complex geometries. Despite its potential to reshape concrete construction, its application in load-bearing elements has been delayed by concerns over weak tensile capacity and challenges in integrating conventional reinforcement. Previous research has shown that post-tensioning provides a reliable method for designing stay-in-place 3D-printed concrete formwork capable of supporting both its self-weight and freshly cast concrete toppings without requiring temporary shoring. However, that work neglected the geometric freedom enabled by 3D printing, as it lacked a comprehensive optimization analysis. This paper introduces a bottom-up optimization workflow consisting of two steps: (I) cross-sectional shape optimization and (II) spanwise optimization. This approach evaluates shapes based on structural performance and demand, then arranges them along the span for higher performance. Given this workflow, two printing strategies, open- and closed-loop, are introduced and compared, and the superior performance of the closed-loop approach is demonstrated.