Abstract
The growth of digitalization has recently prevailed in most of the production sectors, with the exception of the construction industry, in which the use of automation and additive manufacturing (AM) has been restricted to few pioneering applications. Among others, the most promising applications of AM in steel constructions are made with Wire-and-Arc Additive Manufacturing (WAAM) which offers a viable opportunity to build a new generation of efficient steel structures from both automated production and reduced material use, thanks to the freedom in printing highly efficient geometries. Within this framework, it is known that lattice structures are characterized by high efficiency (in terms of high stiffness and minimized material use), however their application at the scale of the single element (meso-scale), such as beams and columns, is still hampered by the issue of the connection at nodes (in terms of geometry complexity, assembly and production cost). Examples of current uses are caulked columns, limited to few high-rate applications. The ambition of the LATTICE project is to propose a new class of efficient structural elements by exploiting the efficiency of lattice structures at the meso scale with WAAM production technology. Indeed, WAAM allows to reduce the scale of truss/lattice systems to the single element by fabricating it as a whole, thus overcoming the issue of the physical node to connect straight parts. To achieve this main objective, the project aims at addressing the following goals: (a) full knowledge on WAAM manufacturing process for lattice meso-elements; (b) assessment of the mechanical properties of their basic components (straight bars and their intersections); (c) development of a computational design procedure for efficient lattice meso-elements accounting for the specific manufacturing, mechanical and structural constraints; (d) development of structural design guidelines for WAAM-produced lattice meso-elements. This requires an interdisciplinary effort in the fields of Structural Design, Manufacturing & Technology and Computational Mechanics, which are the three main research areas involved in the project. LATTICE is articulated in 3 main phases: BASIC, DESIGN, and MESO. Each phase consists of work packages (WP) aimed at designing, testing and validating a physical prototype of lattice meso-column. The BASIC phase will focus on the fabrication and mechanical characterization of the basic components of WAAM lattice meso-elements. The DESIGN phase will focus on the definition of the computational design procedure, through the development of a structural optimization tool for form-finding of lattice structural columns. The MESO phase will focus on the design, testing and validation of a prototype of a lattice meso-column. Lattice structures are largely adopted as efficient systems to reduce the material use while maintaining high performances in stiffness and strength. At the micro scale, the popularity of lattice structures has grown a lot in the recent years: the possibility, in fact, to produce those patterns in a wide variety of materials (polymers, elastomers, metals, light alloys, etc.) made lattice structures interesting in mechanical, naval, aerospace and biomedical field. The synergy between the material characteristics and the shape of the lattice elements allows to specifically tailor the overall characteristics of the lattice-based component. Truss systems are lightweight triangulated systems of straight interconnected structural elements subjected only to axial actions, commonly adopted to cover long span, while reducing the weight and deflection of the building. The critical part of trusses is the connection of each individual element in nodes which can be of various natures. With the advent of additive manufacturing (AM) in almost all production domains, an effort towards the realization of more efficient structures was made through the digitalization of the construction sector. AM processes are proved to create “green” constructions with the support of the Circular Economy, by (i) offering new raw material options, and (ii) simplifying the resource recapture, hence supporting composting and recycling. The flexibility of AM process in creating various geometrical shapes has been used to realize new types of nodes for steel structures, with the aim of reducing the complexity of the construction of truss systems. The most suitable AM process for large-scale steel structures is Wire-and-Arc Additive Manufacturing (WAAM), which adopts two different deposition strategies: the traditional layer-by-layer deposition and the so-called dot-by-dot deposition. The latter allows to realize spatial lattice and diagrid structures, such as the WAAM diagrid column designed at UNIBO and awarded the “Special Mention by Autodesk” at the 3D Pioneers Challenge 2021. The main advantage of WAAM dot-by-dot relies on the possibility to create a new class of lattice structural elements of complex shapes and more efficient material use. Specific considerations must be made when dealing with the structural performances of WAAM elements: (i) the inherent surface roughness, (ii) the marked mechanical anisotropy, (iii) the influence of process parameters. The calibration of the printing parameters in the fabrication process severely alters the mechanical and geometrical features of the structural element. Hence, specific knowledge in manufacturing of WAAM elements should be combined with structural design competences to draw ad-hoc guidelines for their structural application. The use in recent decades of computational design technologies resulted in the development of new structures with formal freedom, often designed to aim for structural efficiency. Nonetheless, current building production still does not allow for such freedom. Hence, the application of computational design tools for free-form design (FFD) was often limited to few explorations in pioneering architectural applications. With the advent of AM process, the use of structural optimization allowed to realize a new generation of optimized structures. However, the focus is mainly on overhang issues and design of supports for fabrication, whereas specific features such as printing orientation and geometrical tolerances are still not accounted. This is the case for most of the formulations currently available for form-finding of gridshells. LATTICE aims at creating a new class of truss elements for structural applications produced with WAAM. The efficiency of the truss system is coupled with the possibility of WAAM technique to overcome the issue of the physical node (as connection of multiple bars) towards a continuous flow of material in which the node becomes only a geometrical entity. Hence, the result is a new generation of node-free trusses. This new class of elements comes from the concept of creating lattice truss systems at the meso scale where its diffusion has been hampered by the complexity, cost and constraint related to conventional nodes. Hereafter, for sake of simplicity, this new class of structural elements will be referred to as lattice meso-elements. Lattice meso-elements are characterized by: (i) the scale of the single element (meso-scale); (ii) straight bars of nominal constant cross-section variously inclined; (iii) a continuous flow of material at the intersection of the straight bars (continuity of the element through the connection of the bars, thus overcoming the traditional concept of the node). In order to provide structural engineers and manufacturers with the know-how to apply lattice meso-elements in construction, a multidisciplinary effort is needed to study the following key aspects: (a) The manufacturing technique proper to obtain lattice steel structural elements; (b) The mechanical properties of the basic components forming lattice meso-elements (i.e. straight bars printed at different inclinations and intersection of bars); (c) The computational design procedure able to include manufacturing and mechanical constraints to create efficient lattice meso-elements. In order to effectively apply lattice meso-elements in steel structures, a strong interdisciplinary effort is envisaged, including inputs and studies from 3 different research fields: (i) Structural Design, (ii) Manufacturing & Technology and (iii) Computational Mechanics. The project will encompass 3 conceptual phases, from the study on the basic components to the design, fabrication and validation of prototype lattice meso-elements; define an overarching computational design procedure for a new class of lattice geometries through the formulation of ad-hoc problems of form finding to include manufacturing and structural constraints of the selected WAAM process and base material; be developed following a direct experimental approach, from the study of the WAAM dot-by-dot printing process to the experimental assessment of the mechanical properties of the basic components, up to the structural performances of physical prototypes of lattice meso-elements. The tangible results of the LATTICE project can be summarized as follows: (1) WAAM printing protocol for dot-by-dot strategy to realize lattice meso-elements; (2) Technical sheet on the mechanical response of the basic components of lattice meso-elements (bars at different inclinations and nodes) accounting for the selected printing process and base material; (3) Computational design protocol for WAAM-produced latticed meso-elements with a dedicated structural optimization tool accounting for the manufacturing and mechanical constraints proper of the printing process and structural application; (4) Physical demonstrator of a lattice meso-column; (5) Technical sheet on the structural response of lattice meso-column; (6) Guidelines for structural design of WAAM-produced steel lattice meso-columns for practitioners and professional engineers.
Dettagli del progetto
Responsabile scientifico: Tomaso Trombetti
Strutture Unibo coinvolte:
Dipartimento di Ingegneria Civile, Chimica, Ambientale e dei Materiali
Coordinatore:
ALMA MATER STUDIORUM - Università di Bologna(Italy)
Contributo totale di progetto: Euro (EUR) 197.048,00
Contributo totale Unibo: Euro (EUR) 94.000,00
Durata del progetto in mesi: 24
Data di inizio
28/09/2023
Data di fine:
28/02/2026
