Lukas Gebhard


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Gebhard

First Name

Lukas

ORCID

0000-0003-0658-5161

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2020 - 202522
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Publications 1 - 10 of 22
  • New structural engineering possibilities of digital fabrication towards leaner concrete structures
    Item type: Presentation
    Mata Falcón, Jaime; Lee, Minu; Gebhard, Lukas; et al. (2022)
    The design possibilities of concrete structures are typically tightly constrained by the high costs and material waste of formworks and reinforcement for producing non-conventional shapes. Digital fabrication technologies aim at producing structures with increased degrees of geometrical freedom at little extra cost and avoiding material waste. This might allow (i) revisiting abandoned structural typologies (e.g. shells, folded roofs, ribbed or mushroom slabs) and (ii) exploring new concepts towards leaner construction. In this lunch talk, researchers from the Group of Concrete Structures and Bridge design at ETH Zurich will present recent structural engineering developments within the domain of Digital Fabrication with Concrete, making use of technologies such as 3D concrete printing, knitted textile reinforcement, robotic reinforcement assemblies and 3D formwork printing.
  • The Nubian Slab: 3D Concrete Printed Stay-in-Place Formwork for Vaulted Slabs
    Item type: Conference Paper
    Jipa, Andrei; Anton, Ana-Maria; Gebhard, Lukas; et al. (2024)
    RILEM Bookseries ~ Fourth RILEM International Conference on Concrete and Digital Fabrication
    The Nubian Slab is a real-world 3D-printed structural concrete element for a residential building in Zurich. The vaulted slab proposes an innovative material-efficient construction method based on digitally fabricated thin shell stay-in-place concrete formworks. The method targets structural slabs, which contribute up to 60% of concrete consumption in architectural applications. The fabrication process is based on the ancient Nubian vaults. These roof structures feature self-supporting inclined masonry courses that can be built without temporary support. This traditional building technique inspired the proposed layered concrete extrusion process, with the 3D-printed concrete layers being analogous to Nubian brick courses. The key difference to conventional 3D concrete printing is the inclination of the extrusion layers, allowing shallow vaults to be produced suspended in thin air without additional supports. The paper presents the robotic 3D-printing setup with a custom nozzle, the fabrication-informed design considerations, and the current limitations of the process, focusing on the case study of a 16 m2 Nubian slab with an irregular perimeter installed in a residential building. Based on this case study, the paper outlines a comprehensive construction sequence for Nubian slabs, considering discrete prefabricated 3D-printed Nubian formworks, assembly details, reinforcement strategies, functional integration, and in-situ monolithic casting. The proposed 3D-printed Nubian slab system enables innovative material-efficient architectural design solutions that may accelerate construction times on site, facilitate mass customisation, automation and integration, and enhance structural performance while remaining compatible with traditional building practices.
  • Pre-installed Reinforcement for 3D Concrete Printing
    Item type: Conference Paper
    Gebhard, Lukas; Bischof, Patrick; Anton, Ana; et al. (2022)
    RILEM Bookseries ~ Third RILEM International Conference on Concrete and Digital Fabrication
    Providing reinforcement is essential for the structural integrity of concrete elements and for safely handling, transporting, and assembling prefabricated concrete parts. However, the integration of reinforcement is a persisting challenge in 3D concrete printing with extruded concrete. This paper presents a production process consisting of 3D printing around pre-installed reinforcement. The reinforcement is composed of conventional reinforcing steel bars, which can be pre-assembled in cages independently of casting, boosting the specialisation and efficiency in production. This approach was used to produce a 3.4 m span T-beam with optimised topology, consisting of three segments connected with matching surfaces. The beam segments were printed upside down, with an open web on top of the flange. Each segment featured reinforcing steel installed in the flange and web. After printing and assembling the segments, a conventional reinforcing bar was inserted in the web as bending reinforcement and grouted subsequently. The structural performance was assessed in a six-point bending test. The fabrication and structural testing of this case study beam showed that pre-installed reinforcement imposes several challenges to the extruder precision, the precision of the bent reinforcement, and – if applied – the casting after printing.
  • Bewehrungsstrategien für Digitale Fertigung mit Beton
    Item type: Presentation
    Gebhard, Lukas (2022)
  • Tor Alva: A 3D Concrete Printed Tower
    Item type: Conference Paper
    Anton, Ana; Lin, Che Wei; Skevaki, Eleni; et al. (2024)
    Fabricate ~ Fabricate 2024: Creating Resourceful Futures
  • Inter-laboratory study on the influence of 3D concrete printing set-ups on the bond behaviour of various reinforcements
    Item type: Journal Article
    Gebhard, Lukas; Esposito, Laura; Menna, Costantino; et al. (2022)
    Cement and Concrete Composites
    This study investigates the influence of different printing set-ups and materials on the bond strength of reinforcement manually placed between 3D printed concrete layers. An identical experimental campaign was performed at two institutes in Switzerland and Italy. Each institute used its own printing process, which consisted either of a set on-demand mix or a high yield stress material. Two types of reinforcement (reinforcing bar Ø8 mm and a high strength steel wire Ø1 mm) and three production configurations (casting and printing with the reinforcement parallel or perpendicular to the printing direction) were investigated. The results showed high bond strength with only a limited influence of the fabrication method for the reinforcing bars. An increased bond was observed for the set on-demand approach compared to the high yield strength material. The comparison with existing models showed that the reinforcing bar bond strength of printed concrete varies slightly from conventional concrete. The high strength wires exhibited poor bond. Based on the gathered experiences, insights into the standardisation of testing for 3D concrete printing are discussed.
  • Interaction of reinforcement, process, and form in Digital Fabrication with Concrete
    Item type: Journal Article
    Kloft, Harald; Sawicki, Bartłomiej; Bos, Freek; et al. (2024)
    Cement and Concrete Research
    Material, manufacturing process, and form are mutually dependent. In formwork-based concrete construction, the reinforcement must be positioned and fixed in the formwork, limiting material efficiency and freedom of form. In Digital Fabrication with Concrete (DFC), the formwork no longer limits the concrete forming process. Furthermore, the reinforcement no longer must be installed in advance, but can be placed before, during or after the concrete application. Therefore, the role of reinforcement and its interaction with processing must be fundamentally rethought in DFC. Furthermore, with reinforcement integration a concrete component expands from a contour-based shape into a structural form. The current paper proposes a new so-called RPF-framework expressing the interaction of reinforcement, process and form in DFC. The application of this framework is illustrated using current examples of DFC, whose structural forms are critically discussed. Finally, the need for a holistic approach to material, process and form in DFC is emphasised.
  • Structural design possibilities of reinforced concrete beams using eggshell
    Item type: Other Conference Item
    Gebhard, Lukas; Burger, Joris Jan; Mata Falcón, Jaime; et al. (2021)
    fib Symposium Proceedings ~ Proceedings of the International fib Symposium on the Conceptual Design of Structures
  • Structural Testing Campaign for a 30 m Tall 3D Printed Concrete Tower
    Item type: Conference Paper
    Giraldo Soto, Alejandro; Gebhard, Lukas; Anton, Ana-Maria; et al. (2024)
    RILEM Bookseries ~ Fourth RILEM International Conference on Concrete and Digital Fabrication. DC 2024
    Digital fabrication with concrete promises a more sustainable and efficient construction industry. However, its implementation is progressing slowly, with hardly any real-scale, load-bearing applications to date. Large-scale structural projects are thus essential to assess the validity of the promise of digital fabrication with concrete. Tor Alva, a 30 m tall tower in the Swiss Alps, is such a project currently being developed to be built in 2024 using digital fabrication with concrete. The tower is a modular system featuring load-bearing 3D Printed Concrete (3DPC) V-columns connecting conventional prefabricated reinforced concrete slabs serving as base and capital. Due to the innovative nature of the columns, structural testing was required to validate their structural integrity. The experimental campaign consisted of a series of structural tests: (i) standard mortar and concrete tests, (ii) compressive loading of a downscaled version of the structural core, (iii) full-scale load tests on a two-metre-tall V-shaped column subjected to vertical and horizontal loading and (iv) direct tensile tests on reinforced 3DPC chords (currently in progress). The standard mortar and concrete tests were needed for 3DPC material characterisation. The compression tests assessed the behaviour of the cross-section under governing compressive load. The overall integrity of the fabrication concept and the connections between the elements were tested with the full-scale load tests. The tensile tests will be carried out to evaluate the performance of reinforced 3DPC chords, which is relevant for columns subjected to bending or tensile forces in case of lateral loading. This paper presents the details of the first three test setups and highlights the main findings of the 3DPC material characterisation and the compression tests.
  • Towards efficient concrete structures with ultra-thin 3D printed formwork: exploring reinforcement strategies and optimisation
    Item type: Journal Article
    Gebhard, Lukas; Burger, Joris Jan; Mata Falcón, Jaime; et al. (2022)
    Virtual and Physical Prototyping
    The Eggshell fabrication process combines the 3D printing of formwork with the simultaneous casting of a fast-hardening concrete. One limiting factor to reaching mass-market adoption is a suitable reinforcing strategy. In this study, a reinforcement strategy combining steel reinforcing bars with steel fibres is explored. A series of eight beams were produced using the Eggshell process or conventionally cast. The longitudinal reinforcement was provided by two reinforcing bars, and two types of fibres, either mixed with the concrete or placed and aligned between the cast concrete layers, were used as shear reinforcement. The results showed that combining conventional longitudinal reinforcement and fibres as shear reinforcement is a suitable strategy. These findings were applied to fabricate an optimised beam with a volume reduction of almost 50%. The structural performance of this beam was similar to the beam with a rectangular crosssection with the same reinforcement strategy showing the potential of Eggshell in combination with an innovative reinforcement strategy to produce material-efficient structural concrete elements.
Publications 1 - 10 of 22