This paper outlines an integrated digital process chain for adaptive modular bridge construction using additive manufacturing and cyber-physical systems. Hierarchical product model structures provide a consistent representation from abstract system level to fabrication-ready modules and enable traceable propagation of changes across detail levels. Principal stress-based toolpath planning links structural behavior directly to robotic fabrication by deriving manufacturable extrusion paths from simulation data. A cyber-physical production system closes the loop by capturing and interpreting manufacturing and inspection data for iterative refinement. Future progress will depend on using these data to train machine learning models for prediction, optimization, and adaptive control. Entwicklung einer konsistenten digitalen Prozesskette vom adaptierbaren modularen Br & uuml;ckenentwurf zur intelligenten additiven Fertigung mittels cyber-physischer SystemeDieser Beitrag skizziert eine integrierte digitale Prozesskette f & uuml;r den adaptiven modularen Br & uuml;ckenbau unter Einsatz additiver Fertigung und cyber-physischer Systeme. Hierarchische Produktmodellstrukturen bieten eine konsistente Repr & auml;sentation von der abstrakten Systemebene bis zu fertigungsreifen Modulen und erm & ouml;glichen die nachvollziehbare Weitergabe von & Auml;nderungen & uuml;ber Detaillierungsebenen hinweg. Eine auf Hauptspannungen basierende Werkzeugbahnplanung verkn & uuml;pft strukturelles Verhalten direkt mit robotischer Fertigung, indem herstellbare Extrusionspfade aus Simulationsdaten abgeleitet werden. Ein cyber-physisches Produktionssystem schlie ss t den Regelkreis, indem es Fertigungs- und Inspektionsdaten erfasst und interpretiert, um iterative Verfeinerungen zu erm & ouml;glichen. K & uuml;nftiger Fortschritt wird davon abh & auml;ngen, diese Daten zum Training maschineller Lernmodelle f & uuml;r Vorhersage, Optimierung und adaptive Steuerung zu nutzen.

This paper discusses the flexural and tensile strength properties of 3D printed concrete, based on the results of a RILEM TC 304-ADC interlaboratory study on mechanical properties. These properties are determined using different testing techniques, including 3- and 4-point flexural tests, splitting tests, and uniaxial tension tests, on specimens extracted from large 3D printed elements in accordance with a prescribed study plan. The relationship between compressive and flexural or tensile strengths, cast or printed samples, different types of tests, and different loading orientations, are analysed to understand the influence of 3D printing. As expected, the strength can reduce significantly when the main tensile stress is acting perpendicular to the interface between layers. The role of deviations from the standard study procedure, in terms of the time interval between the placing of subsequent layers, or the adoption of a different curing strategy, are also assessed. While the increased time interval significantly impacts the strength in the critical direction, the use of variable curing conditions does not seem to have a clear-cut effect on the strength ratios of the printed to cast specimens. Additionally, the paper looks at the variability in the results for the printed specimens, in order to emphasize the need for multiple replicates for obtaining a proper result. An extensive insight into the aspects affecting the variability is presented in the paper. Finally, with the limited dataset available for specimens tested at a larger scale, it is difficult to arrive at a clear understanding of the role of specimen size (i.e., greater number of layers).

Traditional construction techniques, such as in-situ casting and pre-cast concrete methods, have well-established testing protocols for assessing compressive strength and modulus of elasticity, including specific procedures for sample preparation and curing. In contrast, 3D concrete printing currently lacks standardized testing protocols, potentially contributing to the inconsistent results reported in previous studies. To address this issue, RILEM TC 304-ADC initiated a comprehensive interlaboratory study on the mechanical properties of 3D printed concrete. This study involves 30 laboratories worldwide, contributing 34 sets of data, with some laboratories testing more than one mix design. The compressive strength and modulus of elasticity were determined under three distinct conditions: Default, where each laboratory printed according to their standard procedure followed by water bath curing; Deviation 1, which involved creating a cold joint by increasing the time interval between printing layers; and Deviation 2, where the standard printing process was used, but the specimens were cured under conditions different from water bath. Some tests were conducted at two different scales based on specimen size—“mortar-scale” and “concrete-scale”—to investigate the size effect on compressive strength. Since the mix design remained identical for both scales, the only variable was the specimen size. This paper reports on the findings from the interlaboratory study, followed by a detailed investigation into the influencing parameters such as extraction location, cold joints, number of interlayers, and curing conditions on the mechanical properties of the printed concrete. As this study includes results from laboratories worldwide, its contribution to the development of relevant standardized testing protocols is critical.

Research in digital fabrication, specifically in 3D concrete printing (3DCP), has seen a substantial increase in publication output in the past five years, making it hard to keep up with the latest developments. The 3DCP.fyi database aims to provide the research community with a comprehensive, up-to-date, and manually curated literature data set documenting the development of the field from its early beginnings in the late 1990s to its resurgence in the 2010s until today. The data set is compiled using a systematic approach. A thorough literature search was conducted in scientific databases, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) scheme. This was then enhanced iteratively with non-indexed literature through a snowball citation search. The authors of the articles were assigned unique and persistent identifiers (ORCID® IDs) through a systematic process that combined querying APIs systematically and manually curating data. The works in the data set also include references to other works, as long as those referenced works are also included within the same data set. A citation network graph is created where scientific articles are represented as vertices, and their citations to other scientific articles are the edges. The constructed network graph is subjected to detailed analysis using specific graph-theoretic algorithms, like PageRank. These algorithms evaluate the structure and connections within the graph, yielding quantitative metrics. Currently, the high-quality data set contains more than 2600 manually curated scientific works, including journal articles, conference articles, books, and theses, with more than 40000 cross-references and 2000 authors, opening up the possibility for more detailed analysis. The data is published on https://3dcp.fyi , ready for import into several reference managers, and is continuously updated. We encourage researchers to enrich the database by submitting their publications, adding missing works, or suggesting new features.

Additive manufacturing of cementitious materials is a rapidly growing branch of manufacturing both in research and industry, particularly the variant of material deposition by extrusion. This process results in a strong anisotropy in mechanical properties, owing largely to the interfaces between adjacent filaments. This anisotropy is even more pronounced when fiber reinforced mortars or continuous entrained reinforcement components such as cables are used. To exploit orientation-dependent performance, the print path can be designed to align with the principal (tensile) stress trajectories. However, obtaining an appropriate print path based on this concept poses several challenges, related to the filling of intermediate spaces between two trajectories. In this paper, an approach for planning such a robot toolpath is presented, elaborated, and illustrated by means of a case study on a well-known reference case. The main features of the tool planning method are the relaxation of the offset width, the avoidance of toolpaths with acute angles by intersecting offset curves, and a continuous toolpath.

In order to enable the prefabrication of bridge structures in a continuous production line, extensive changes in design and -execution are necessary. Therefore, this paper explains a holistic and end-to-end digital design process for a modular construction system that composes planar, additively manufactured modules. The system is computationally represented with a graph-based data model, laying the foundation for design automation employing graph rewriting rules. Sets of rules are employed to generate modular structures according to two approaches: Either existing component geometries are segmented, or rules formalize the aggregation of structures. At this process state, predominantly geometric information is available. This information is developed into a semantically rich representation of the decomposition until a highly detailed production model for each module can be instantiated parametrically. Because of the flexible definition based on NURBS, the production model can depict a variety of possible joining situations and connections. Beyond this, the model is the basis of the printing path generation for the additive manufacturing process. The path is determined according to the principal stress directions, numerically interpolating the results of a non-linear FE analysis. Along this printing path, the alignment of carbon fibre reinforcement is steered by custom nozzle technology, enabling outstanding material properties of the manufactured components.

Zum Titelbild: Die außergewöhnlich schlanke Fußgängerbrücke aus Hochleistungsbetonfertigteilen besitzt eine Hauptspannweite von 76 m bei einer Höhe von 1,80 m.Sie verbindet

Für die Vorfertigung von Brückentragwerken in industrieller Fließfertigung sind weitreichende Veränderungen in Entwurf und Ausführung nötig. Deshalb erläutert dieser Aufsatz einen ganzheitlichen und durchgängig digitalen Planungsprozess für eine modulare Bauweise mit ebenen, additiv gefertigten Grundmodulen. Als Grundlage eines automatisierten Entwurfs wird das System mithilfe eines graph‐basierten Modells abgebildet, darauf aufbauende Graphersetzungsregeln erzeugen modulare Tragwerke gemäß zweier Herangehensweisen: Einerseits werden bestehende Bauteilgeometrien segmentiert, andererseits formalisieren Regeln die Aggregation zu Strukturen. Die zu diesem Prozessschritt vorrangig geometrische Information wird in eine semantisch reichhaltige Darstellung der Zerlegung entwickelt, sodass daraus ein hochdetailliertes Produktionsmodell für jedes Modul parametrisch instanziiert werden kann. Dieses Modell ist durch die flexible Beschreibung mit NURBS in der Lage, eine Vielzahl an Verbindungs‐ und Fügesituationen abzubilden. Schließlich fungiert es auch als Grundlage der Pfadgenerierung für die additive Fertigung. Der Druckpfad wird dabei entlang den Hauptzugspannungsrichtungen ermittelt, durch numerische Interpolation der Ergebnisse einer nichtlinearen FE‐Analyse. Entlang dieses Pfades wird die Ausrichtung von Carbonfaserbewehrung mithilfe angepasster Düsentechnik gesteuert, wodurch herausragende Materialeigenschaften der gefertigten Komponenten erreicht werden können.

The basis of correct numerical simulations is the knowledge of the material behavior under uniaxial compressive and tensile loading. In particular, the behavior under tensile stresses is of importance for steel fiber reinforced concrete due to its post cracking tensile strength. This paper presents an algorithm to determine the centric tensile stress-crack-width relationship of steel fiber reinforced concrete. The input data is a load-crack-width curve obtained from flexural tensile tests. Within the context of an inverse analysis, the tensile behavior is determined using B-Splines, which allow for high approximation quality due to the variable combination of the number of control points and the polynomial degree. Based on the results obtained from inverse analysis, numerical simulations of deflection-softening and -hardening notched 3-point flexural tensile tests on steel fiber reinforced concretes are carried out, the results of which are compared against the experimental results. With the obtained constitutive relationship, a very good agreement between simulated and experimentally observed concrete structural behavior is shown.

Zusammenfassung Grundlage realitätsnaher numerischer Berechnungen ist die Kenntnis des Betontragverhaltens unter einaxialer Druck- und Zugbeanspruchung. Insbesondere das Verhalten unter Zugbeanspruchung ist bei Stahlfaserbetonen gegenüber unbewehrtem Beton aufgrund seiner ausgeprägten Nachrisszugfestigkeit von besonderer Bedeutung. Im vorliegenden Beitrag wird ein Algorithmus zur Ermittlung der zentrischen Zugspannungs-Rissöffnungs-Beziehung von Stahlfaserbeton vorgestellt. Als Eingangswert dient eine aus Biegezugversuchen erhaltene Kraft-Rissöffnungs-Kurve. Im Rahmen einer inversen Analyse wird das Zugtragverhalten unter Anwendung von B-Splines bestimmt, die aufgrund der variablen Kombination der Kontrollpunktanzahl und des Polynomgrades eine hohe Approximationsgüte ermöglichen. Beispielhaft wird anschließend der entwickelte Algorithmus durch numerische Nachrechnungen von experimentell durchgeführten, gekerbten 3-Punkt-Biegezugversuchen aus Stahlfaserbetonen mit unter- und überkritischen Nachrisstragverhalten validiert. Mit der gewonnenen konstitutiven Beziehung kann eine sehr gute Übereinstimmung zwischen simuliertem und experimentell beobachtetem Betontragverhalten gezeigt werden.