Giulivo, Marco (2025) Analytical and Experimental Investigation of Digitally Fabricated Concrete Structures: A Design-Oriented Framework and Case Study Validation. [Tesi di dottorato]

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Abstract

This doctoral work develops and validates an innovative analytical and design framework for the structural use of digitally fabricated concrete wall structures, with particular focus on 3D-printed concrete (3DPC) fabrication additive manufacturing technology. The main objective is to provide a mechanical and structural interpretation of the behaviour of these novel printed elements, by analysing the close relationship between digital fabrication process parameters—such as interlayer time (ILT), printing path geometry, and deposition strategy—and the resulting mechanical response across multiple scales of investigation: material, intermediate, and structural. To this end, an extensive multi-scale experimental campaign was carried out to characterise the key compressive, tensile, and shear strength parameters, following RILEM recommendations and drawing analogies with masonry testing standards. At the structural scale, diagonal compression and in-plane cyclic tests on 3D-printed walls were performed to investigate their seismic behaviour. The results showed that, when tensile strength is neglected, the walls exhibit a behaviour comparable to that of traditional masonry; however, when tensile resistance is considered at the Ultimate Limit State (ULS), the in-plane shear strength can reach values up to three times higher than those predicted by conventional masonry formulations. These findings motivated the development of in-plane resistance domains specifically tailored for 3DPC walls, highlighting the differences between analyses that include or exclude tensile strength, and comparing the outcomes with reference masonry typologies available in the literature. Since tensile resistance is strongly affected by printing parameters, a parametric analysis was conducted by varying the interlayer time (ILT) while keeping the main geometric and mechanical properties constant. This study enabled the creation of preliminary design framework, which will be further validated through future large-scale experimental campaigns. In parallel, the experimental and analytical results were employed for the numerical calibration of a simplified finite element (FEM) model implemented in SAP2000, based on a linear interpretation of the structural response. This model allows for a rapid and code-consistent structural assessment, bridging advanced experimental research with traditional engineering design tools and promoting the practical adoption of 3DPC in real structural applications. The proposed methodology was finally applied to the Montalto di Castro Control Room, the first structural 3D-printed concrete building constructed in a seismic zone, verified according to the Italian Building Code (NTC 2018). In this application, the wall was analysed following a conservative design approach, assuming brittle behaviour and neglecting tensile strength to ensure structural safety within the current regulatory framework. Overall, this PhD work demonstrates that 3D-printed concrete—despite its intrinsic anisotropy, interlayer bonding mechanisms, and process-dependent geometric features—can be effectively interpreted and governed through the principles of classical structural mechanics. By integrating experimental investigation, numerical modelling, and code-based verification, the structural behaviour of 3DPC walls can be described through a set of main parameters: layer orientation, tensile and shear interface properties, wall slenderness, void ratio, and printing path geometry.

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