Formwork-free flow production of adaptive support structures from variable frame elements – ACDC

Project description

Due to their high load-bearing capacity and stiffness, combined with low weight and material usage, shells are one of the most effective surface-forming load-bearing structures. However, the consistent implementation of load-adaptive design principles in the construction of shell structures is restricted by very high planning and manufacturing costs. This project aims to develop new approaches for the effective, industrial, and economical production of shell structures by approximating them with numerous similar facets. The application of planar quadrilateral faceting results in a discretized shell structure comparable to a gridshell structure, cf. Fig. 1.
Computer-aided algorithms are being developed for the geometrical description of the free-formed supporting structures and their faceting, in which strategies for the architectural and constructive elaboration of the modules are also implemented. This forms the basis for a consistent digital model, which is used to represent both the parametric modelling of the structure and the determination of the facets' shape as well as the generation of digital data sets for the automated production of the modules.
The modules are divided into an edge zone and an infill. The boundary zone consists of ultra-high strength, highly ductile concrete with short polymer fibres and defines the form-fitting edge geometry to the adjacent modules in longitudinal axis and cross section. This concrete type reacts well to local load peaks and ensures a high robustness of the module edges. The infill can be done in different ways, which increases the changeability of the module. Initially, it should be done with a thin layer of textile-reinforced concrete. The textile reinforcement will be produced in a load-bearing manner by depositing carbon yarns. Alternatives such as semi-finished grid products are also being investigated.
The modules are produced automatically in a flow production process. The edge of the module is formed by the end effector of an extruder without the need for formwork and with a variable cross-section. The reinforcement yarns are impregnated inline with a mineral suspension of finest material and positioned with the help of a yarn depositing unit. The infill is filled with concrete as required. The automated tool guidance results from the continuous digital data model, which also serves for quality monitoring.
The freedom in shaping and the variable choice of materials, which is achieved on the basis of digital algorithms, enable the production of components that overcome the contradiction between serial production and individuality.

Poster on the project contents

Load-bearing concrete shell structures are very efficient due to their high load-bearing capacity and stiffness, combined with low weight and minimized material usage. Despite all the advantages the use of such structures has not yet been widespread, the main reasons having to do with the difficulties in their design and construction. The fabrication of thin concrete shell structures by traditional casting methods requires the time-consuming creation of a unique, very expensive formwork and also leads to large amounts of industrial waste since its reuse is seldom possible.
This project aims to develop new approaches for the effective, industrial, and economical fabrication  of shell structures without formwork by assembling them from automatically produced, prefabricated modules. Computer-aided algorithms are being developed for the geometrical description of the free-formed supporting structures and their faceting, in which strategies for the architectural and constructive elaboration of the modules are also implemented. Dealing with free-form architecture and its properties, in order to create production-aware design, methods from discrete differential geometry are to be implemented. Here the properties of the single module are in focus. At this stage planar modules and planar connection sides are considered (no geometry torsion) as well as their scalability and adaptability. Among others, we use circular mesh systems generation (see Figure 1), planar curves subdivision and Christoffel duality methods for model’s parametrization and further structural and material optimization. These methods are implemented in the form of algorithms for Grasshopper that enable us to generate the parametrized models and further optimize them. The goal is to have more control of the subdivision process on the local level, but also offer a wide range of designs that are both possible to prefabricate and structurally efficient.
The prefabrication of modules is divided into five sub-processes, each of them is fully automated; see Figure 2.  In the first step, the edge zone of the module is 3D printed using Strain-Hardening Cement-based Composite (SHCC). This is an ultra-high strength and a highly ductile material reinforced with short polymer fibers. The use of SHCC not only ensures that high load-bearing capacity and dimensional stability are attained, but also that very high local stresses, e.g. during transport and assembly, can be sustained. In the second step, the inner part of the module is filled with concrete, which can be pumped, sprayed, or poured, depending on the concrete type in use and the available machinery. The third step is reinforcing of the fill-in with a carbon textile mesh. This material was chosen due to its high tensile strength and durability. Due to its high chemical resistance, the concrete cover can be reduced to a few millimeters, which enables the production of very thin structures. Shortly before or directly during the mesh production, yarns can be coated with a specially developed mineral micro-suspension, which considerably enhances its bond towards concrete matrix as well as the performance of the reinforcement at elevated temperatures. In the fourth step, the second layer of the outer edge is printed. To complete the module production, in the fifth step the area within the printed edges is filled with concrete.  
As the first stage of illustrating the potential of the proposed technology, a demonstrator called ConDIT 1.0 – a sphere-like shell structure composed of several frames – was designed and built. The frame modules were fabricated automatically using extrusion-based 3D printing and a printable SHCC. To further challenge the technology, the second demonstrator called Double-Arch is built. The construction consists of two folded symmetric arc-like strips. The challenging geometry task was to achieve the same angles between modules planes. This time direct module-to-module connections are gained with 7 different types of modules printed from which 4 bottom ones are done with concrete infill with SCC. Structural analysis has been conducted in order to establish the final design of the demonstrator. As the next step, the authors aim to pursue the design and implementation of the space frame structures and integrate the possibility of curved modules prefabrication.