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Double-curved precast concrete elements: Research into technical viability of the flexible mould method

14 Sep 2015-
TL;DR: In this paper, the authors present a review of the state-of-the-art flexible formwork methods for precast concrete elements with complex, double-curved geometry.
Abstract: The production of precast, concrete elements with complex, double-curved geometry is expensive due to the high costcosts of the necessary moulds and the limited possibilities for mould reuse. Currently, CNC-milled foam moulds are the solution applied mostly in projects, offering good aesthetic performance, but also resulting in waste of material, relatively low production speed and fairly high costs per element. The flexible mould method aims to offer an economic alternative for this state of art technology by allowing repeated reuse of the same mould, and if necessary, reuse in adapted shape. A patent and literature review and comparison of state-of-art formwork methods reveals that, although the idea of a flexible formwork already dates from the mid-20th century, in building industry it has not yet found widespread application, and is still experimental to a large extent. In other industries, such as aerospace and automotive, flexible moulds are occasionally used for rapid prototyping purposes, mostly for the forming of thin metal sheets. The understanding of the flexible mould principle in terms of mechanics is still in development. In combination with concrete, the flexible mould has been industrially applied only on occasion. Deliberately imposed deformation of concrete after casting allows the use of only one single-sided flexible mould, but - being a method quite alien to normal precast concrete production - has hardly been investigated. Therefore, models are needed both for the flexible layer as well as it's use in combination with concrete. By analysing a number of architectural cases in terms of geometrical aspects, more information is gathered about building size, element thickness, curvature radius and number and type of elements. This information is used to define the type of shapes for which the flexible mould method would be suitable. Through the last 80 years, the shape of curved architecture has changed; whereas the early famous shell designers such as Isler and Torroja aimed for structurally optimized and material-efficient shapes, nowadays these shapes have mostly made place for free-form curves, in which parametric design or sculptural influences are leading. For larger projects, several hundreds to even thousands of uniquely curved elements are manufactured, varying in curvature radius in a range between 0.75 m and 45 m. Furthermore the contours and edge position can vary from element to element. Prediction of each element's edge position is non-trivial for the flexible mould method, especially not for elements with strong curvature. The deformation process can be described mathematically by analysing thecurvature parameters. An important and meaningful parameter is the Gaussian curvature. Depending on the change in Gaussian curvature, the imposed deformation of the mould surface and the concrete results in certain amounts of bending action (B) and in-plane surface stretching (S). Bending tensile strains in the still plastic concrete can be in the range of 25 to 50‰ for an element with 50 mm thickness, which is far more than the values normally encountered in concrete after casting. The application of in-plane shear deformation appears to be helpful to deform the mould from flat to double-curved. The exact positioning of the element edges can be determined from this in-plane shear deformation. The shape of the mould, in the present research, is controlled by a grid of actuators - extendible support points that follow the intended architectural shape. As mould surface, a thin rubber layer can be used, that, however, has to be supported by a material that is capable of carrying the weight of the concrete without visible deflection between the actuators. Various solutions are investigated for this support material, of which the strip mould offers the most accurate results and predictability. As said, the concrete in this method is deliberately deformed after casting in an open, single-sided mould. This requires control over both the fluidity and strain capacity of the fresh concrete: if the concrete is too fluid, it will flow out of the mould after deformation due to the slope of the mould, if it is already too stiff, cracks may occur. Various experiments are conducted to investigate the viability of the principle as well as the parameters that influence the risk of either flow or cracking. It appears that the use of a self-compacting concrete with thixotropic properties reduces both the risks: as a result of quick stabilisation after casting, the yield strength build-up will prevent flow once the mould is deformed and put at a certain slope. Thanks to it's plastic strain capacity, this type of concrete will be able to undergo the imposed deformation without cracking. An important measure to prevent this cracking is the curing of the concrete directly after casting and a deformation that takes place before initial setting time. Thin steel rebar, glass-fibre textiles or mixed fibres are all applicable as reinforcement, the latter two giving the best results. For the measurement of yield strength development of the concrete mixture before and after casting, various methods are investigated. Literature research and experiments demonstrate that, once the rheological behaviour of a mixture has been determined with a viscometer accompanied with slump (flow) tests, the correct moment of deformation of the flexible mould can later be determined from repeated slump (flow) tests with sufficient reliability. However, as soon as the mixture constituents will be adapted, new viscometer measurements have to be carried out again. The flexible mould method has been successfully tested on single- and double-curved precast concrete elements with a radius down to 1.50 m and an element thickness up to 50 mm. Until this moment, the maximum element size tested was approximately 2 x 1 m2, but larger elements are expected to be feasible. An integrated design-to-production process is required: due to the complex geometry and the impact of this geometry on all aspects of the manufacturing, all parties involved should cooperate to make the use of this method possible. Computational skills are needed to determine design parameters and control the manufacturing process. Several new questions were identified during the research, but at this moment, implementation of the flexible mould method in an industrial environment in cooperation with a concrete product manufacturer is the best way to determine the priorities for further research. From the full research it is concluded that the flexible mould method is viable for the production of double-curved concrete elements.
Citations
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Journal ArticleDOI
TL;DR: A review of the state of the art in the newly forming field of digital fabrication with concrete, and aims to provide some direction in terms of the research challenges encountered thus far is provided in this article.

274 citations

Journal ArticleDOI
TL;DR: In this paper, the authors explore flexible formwork construction technologies which embrace the fluidity of concrete to facilitate the practical construction of concrete structures with complex and efficient geometries, highlighting practical uses, research challenges and new opportunities.
Abstract: Concrete is our most widely used construction material. Worldwide consumption of cement, the strength-giving component of concrete, is estimated at 4.10 Gt per year, rising from 2.22 Gt just ten years ago [1]. This rate of consumption means that cement manufacture alone is estimated to account for 5.2 % of global carbon dioxide emissions [2]. Concrete offers the opportunity to economically create structures of almost any geometry. Yet its unique fluidity is seldom capitalised upon, with concrete instead being cast into rigid, flat moulds to create unoptimised geometries that result in high material use structures with large carbon footprints. This paper will explore flexible formwork construction technologies which embrace the fluidity of concrete to facilitate the practical construction of concrete structures with complex and efficient geometries. This paper presents the current state of the art in flexible formwork technology, highlighting practical uses, research challenges and new opportunities.

77 citations

Journal ArticleDOI
Mariana Popescu1, Lex Reiter1, Andrew Liew1, T. Van Mele1, Robert J. Flatt1, Philippe Block1 
TL;DR: The hybrid approach results in an ultra-lightweight formwork that is easily transportable and significantly reduces the need for falsework support and scaffolding, which has many advantages on the construction site.

60 citations

Journal ArticleDOI
TL;DR: In this research paper a new methodology for 3D Printing Concrete onto a temporary freeform surface is presented, achieved by setting up a workflow for combining a Flexible Mould developed at TU Delft with a 4-degrees-of-freedom gantry printer provided by TU Eindhoven.

50 citations


Cites background or methods from "Double-curved precast concrete elem..."

  • ...The adaptable mould [5] used in this study is a flexible surface defined by adjusting an underlying pinbed (Figs....

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  • ...E-mail addresses: h.r.schipper@tudelft.nl (H.R. Schipper), F.P.Bos@tue.nl (F.P. Bos)....

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  • ...3D Printing Concrete on temporary surfaces: The design and fabrication of a concrete shell structure C. Borg Costanzi, Z.Y. Ahmed, H.R. Schipper⁎, F.P. Bos⁎⁎, U. Knaack, R.J.M. Wolfs...

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  • ...Delft University of Technology 3D Printing Concrete on temporary surfaces The design and fabrication of a concrete shell structure Borg Costanzi, C.; Ahmed, Z. Y.; Schipper, H. R.; Bos, F. P.; Knaack, U.; Wolfs, R. J.M. DOI 10.1016/j.autcon.2018.06.013 Publication date 2018 Document Version Accepted author manuscript Published in Automation in Construction Citation (APA) Borg Costanzi, C., Ahmed, Z. Y., Schipper, H. R., Bos, F. P., Knaack, U., & Wolfs, R. J. M. (2018)....

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  • ...An Adaptable Mould layout consists of a Deformable Steel mesh attached to a 1m×1m pin bed [5]....

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Journal ArticleDOI
TL;DR: In this article, the structural performance of fabric formworks has been surveyed and classified into seven themes: feasibility studies and manufacturing methods of complex structural elements, finite element modelling, structural optimizing and form-finding themes, Durability, sustainability, efficiency and quality improvement, cable-net fabric formwork theme, stayin-place structural formworks theme, and review papers.
Abstract: Article history: Received 8 July, 2019 Accepted 22 August 2019 Available online 22 August 2019 Fabric Formworks which are made using textile sheets such as Polyolefin, Polyesters/Polyethylene Terephthalate, nylon and Polypropylene are being used instead of conventional formworks in the construction industry. This article summarises significant studies and provides an updated review of references on the structural performance of fabric formworks over the last decade. The survey showed that they could be categorised into seven themes; namely, “Feasibility studies and manufacturing methods of complex structural elements”; “Finite element modelling, structural optimizing and form-finding themes”; “Pneumatic / Vacuumatic formwork theme”; “Durability, sustainability, efficiency and quality improvement”; “Cable-net fabric formwork theme”; “Stayin-place structural formworks theme”; and “Review papers”. These categories comprise about 25%, 17%, 15%, 15%, 10%, 6% and 6% of related studies respectively. © 2020 Growing Science Ltd. All rights reserved.

17 citations


Cites methods from "Double-curved precast concrete elem..."

  • ...Also, Schipper (2015) studied on fabric formworks and technical notes of the flexible formwork method to build the double-curved precast structural concrete elements during his doctoral degree thesis....

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References
More filters
Journal ArticleDOI

16,374 citations


"Double-curved precast concrete elem..." refers methods in this paper

  • ...According to the research design technique described by Creswell (2009), variables under consideration in a research can be distinguished in, among others, independent and dependent variables, which roughly are similar to causes and effects....

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Journal ArticleDOI
TL;DR: In this article, a modified constitutive relation that applies everywhere in the flow field, in both yielded and practically unyielded regions, is proposed to analyze two-dimensional flows of Bingham fluids.
Abstract: Steady, two‐dimensional flows of Bingham fluids are analyzed by means of a modified constitutive relation that applies everywhere in the flow field, in both yielded and practically unyielded regions. The conservation equations and the constitutive relation are solved simultaneously by Galerkin finite element and Newton iteration. This combination eliminates the necessity for tracking yield surfaces in the flow field. The analysis is applied to a one‐dimensional channel flow, a two‐dimensional boundary layer flow, and a two‐dimensional extrusion flow. The finite element predictions compare well with available analytic solutions for limiting cases.

1,177 citations


"Double-curved precast concrete elem..." refers background in this paper

  • ...2 Differences between solids and fluids according to Bingham Although the term ’Bingham’ in most concrete-related literature is linked to the term ’fluid’, it was found (Bingham, 1922; Oldroyd, 1947; Papanastasiou, 1987) that a solid material that can support a finite stress elastically without flow, and that flows with constant (or plastic) mobility when the stresses are sufficiently great, in some literature is called a Bingham solid....

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Book
01 Jan 1922

997 citations


"Double-curved precast concrete elem..." refers background in this paper

  • ...In Bingham’s view, fluids and solids are dealt with in the same way. Hardening concrete can be seen as a Bingham solid; the yield criterion for such a solid is identical to the Tresca yield criterion that is used in theory of plasticity. 2. Further empirical material was found on the relation between slump (flow) and shear yield strength; this can be used in the further research to calculate the yield strength from slump tests; for very fluid concrete this empirical relation is more accurate than for stiffer mixtures, where a significant spread between the various equations was found. 3. Tests with a viscometer need to be carried out to obtain calibrated data as well as data on thixotropic behaviour and viscosity. 4. The strains resulting from imposed deformation can be split in a contribution from out-of-plane bending (B) and one from in-plane strains (S) resulting from elongation, compression or shear; these strain components, when added, are expected to be in the range of tens of ‰ (tens of thousands of micro-strains), depending on curvature radius and element height; based on publications of Hammer (2007) and Dao et al. (2009), that both report on the tensile properties of early-age concrete, in combination with the findings during the viability study, it is expected that an SCC in the first hour after casting will have sufficient strain capacity to take the imposed deformation without cracking....

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  • ...2 Differences between solids and fluids according to Bingham Although the term ’Bingham’ in most concrete-related literature is linked to the term ’fluid’, it was found (Bingham, 1922; Oldroyd, 1947; Papanastasiou, 1987) that a solid material that can support a finite stress elastically without flow, and that flows with constant (or plastic) mobility when the stresses are sufficiently great, in some literature is called a Bingham solid....

    [...]

  • ...More specifically, directly after mixing, fresh concrete is often modelled as a Bingham fluid, a subset of non-Newtonian fluids (Bingham, 1922; Ferraris and De Larrard, 1998; Wallevik, 2005; Roussel et al., 2005; Kovler and Roussel, 2011)....

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Book
22 Dec 2005
TL;DR: The Finite Element Method for Fluid Dynamics as discussed by the authors is a complete introduction to the application of the finite element method to fluid mechanics and includes a useful summary of all relevant partial differential equations before moving on to discuss convection stabilization procedures, steady and transient state equations, and numerical solution of fluid dynamic equations.
Abstract: The Finite Element Method for Fluid Dynamics offers a complete introduction the application of the finite element method to fluid mechanics. The book begins with a useful summary of all relevant partial differential equations before moving on to discuss convection stabilization procedures, steady and transient state equations, and numerical solution of fluid dynamic equations. The character-based split (CBS) scheme is introduced and discussed in detail, followed by thorough coverage of incompressible and compressible fluid dynamics, flow through porous media, shallow water flow, and the numerical treatment of long and short waves. Updated throughout, this new edition includes new chapters on: * Fluid-structure interaction, including discussion of one-dimensional and multidimensional problems. * Biofluid dynamics, covering flow throughout the human arterial system. Focusing on the core knowledge, mathematical and analytical tools needed for successful computational fluid dynamics (CFD), The Finite Element Method for Fluid Dynamics is the authoritative introduction of choice for graduate level students, researchers and professional engineers. * A proven keystone reference in the library of any engineer needing to understand and apply the finite element method to fluid mechanics. * Founded by an influential pioneer in the field and updated in this seventh edition by leading academics who worked closely with Olgierd C. Zienkiewicz. * Features new chapters on fluid-structure interaction and biofluid dynamics, including coverage of one-dimensional flow in flexible pipes and challenges in modeling systemic arterial circulation.

729 citations

Book
01 Jan 1983
TL;DR: This book tackles the fundamental question of how bending and stretching effects combine and interact in shell structures from a physical point of view; and it shows that this approach leads to an understanding of the structural mechanics of shells in general, and to useful results in particular problems.
Abstract: Shell structures form key components in a very wide range of engineering enterprise. The theory of shell structures is an old and large subject, with a huge literature. However, this book is not a compilation of results from the past. Instead, it is an attempt to bring the essence of the subject within the grasp of engineers. It tackles the fundamental question of how bending and stretching effects combine and interact in shell structures from a physical point of view; and it shows that this approach leads to an understanding of the structural mechanics of shells in general, and to useful results in particular problems. The first half of the book is concerned mainly with the basic ideas and equations of equilibrium, geometry and elasticity, and their combination in various useful ways. In particular, it includes a simple treatment of the geometry of general curved surfaces. The second half of the book first investigates the behaviour of various practical shell structures under static loading. Then there are chapters on the buckling of shells, on vibration, and on the application of plastic theory to analysis and design.

663 citations


"Double-curved precast concrete elem..." refers background or methods in this paper

  • ...Eigenraam (2013) studied the work of Calladine (1983) and found there very useful tools to describe and understand the flexible mould process....

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  • ...A derivation of this equation is given by Calladine in Chapter 6 of his book [Calladine, 1983]....

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  • ...The textbook ”Theory of Shell Structures” of Calladine (1983) appeared very helpful for the further study....

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  • ...Used for defining the measure of curvature [Calladine, 1983]....

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