Frei geformte Betonbauteile: Finden einer Fertigungsmethode

Due to the complexity of the freeform shapes it is often not possible to distinguish any repetitive elements in freeform buildings at all. Most freeform building designs consist of many single or double curved surfaces which require complex shapes for the mould and element edges. Since the costs of the moulds (formwork) for precast concrete make up a significant percentage of the final price per element or per square meter, the feasibility of freeform buildings in precast concrete is still far from optimal. The PhD research carried out at Delft University of Technology, Faculty ofCivil Engineering, aims to improve the applicability of precast concrete through the development of a flexible mould. At the end of the research the design specifications of vital parts of the flexible mould should be described, and supported by theoretical and experimental study as a proof of concept.Structural EngineeringCivil Engineering and Geoscience

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

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\u89 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.Structural EngineeringCivil Engineering and Geoscience

ПРОИЗВОДСТВО БЕТОННЫХ ЭЛЕМЕНТОВ С ДВУМЯ КРИВОЛИНЕЙНЫМИ КОНТУРАМИ - ПРИМЕНЕНИЕ ПЕРЕДОВЫХ ПРОИЗВОДСТВЕННЫХ МЕТОДОВ В СОЗДАНИИ СВОБОДНЫХ АРХИТЕКТУРНЫХ ФОРМ Manufacturing of Double-Curved Concrete Elements: Enabling free-form architecture through advanced manufacturing methods

В современных архитектурных решениях широко используется криволинейность свободных форм. Именно поэтому изогнутые элементы из сборного бетона могут быть потенциальным рын- ком для производителей. В прошлом не существовало просто- го способа для производства таких компонентов. Исследования, проводимые в докторантуре Дельфтского Технического универ- ситета, направлены на разработку такого метода. Как теорети- ческие исследования, так и испытания, показывают, что новый метод, при котором сначала происходит заливка бетона, а потом его изгиб в гибкой опалубке, является практически возможным и обладает конкретными преимуществами, как то: при его при- менении относительно легко регулировать толщину элемента, нет необходимости использовать контрформу, гибкая опалуб- ка позволяет свободно и многократно изменять форму опалуб- ки и поэтому использовать ее повторно раз за разом. Оптими- зация бетонных смесей позволяет сократить цикл. Планирует- ся провести больше испытаний в ближайшем будущем в целях дальнейшей разработки самого метода и оборудования. При- глашаем партнеров из промышленных и академических кругов к участию в проекте для совместной работы по разным темам, необходимой для успешного полномасштабного применения этой технологии на практике. Current architectural designs make extensive use of curvature in free-form shapes. Curved elements in precast concrete therefor form a potential market for concrete manufacturers. A simple method to produce this type of elements was not available in the past. A PhD research at TU Delft aims to develop such a method. The theoretical research and the tests demonstrate that a new technique of first casting and later deforming concrete in a flexible mould is feasible and has several advantages: it is a relatively easy way to control element thickness, there is no need for a contra mould, the flexible mould gives freedom to adjust the shape of the mould multiple times and thus reuse it time after time. By optimizing the concrete mixture, a short cycle time can be reached. In the near future more tests are planned to further develop and improve the method and equipment. Industrial or academic partners are invited to participate in the project, to work together on the different topics necessary to make this technology ready for full scale application in practice.Design and ConstructionCivil Engineering and Geoscience

Efficient material use through smart flexible formwork method

Concrete is an excellent material for application in free-form architecture as a result of its initial fluid state. Double-curved building shapes have been realized in various fibre-reinforced mixtures, using advanced CNC-milled formwork systems. However, a substantial reduction of material use is still possible on two ends: by using a flexible formwork very thin and structurally efficient elements can be manufactured, reinforced with fibres or textiles. Moreover, the reusability of the flexible formwork considerably limits the waste material that was always remaining after the use of milled formwork systems. This paper discusses experiments with both formwork and mixtures in a PhD-study of the first author, demonstrating the ecological potential of this innovative production method.Structural EngineeringCivil Engineering and Geoscience

Concepts and prototypes for flexible moulds for production of double curved elements

Flexible moulds for production of double curved elements could offer a solution for challenges in realizing freeform architectural design which tends to be costly and time consuming. However developments are still ongoing and promising methods that result in highly accurate elements still remain to be proven. When surfaces are deformed into a specific shape inaccuracies occur easily due to bucking or wrinkling of the surfaces. In this paper a number of concepts are presented which can be used to prevent these effects. The concepts are based on a fundamental relationship between change of Gaussian curvature of surfaces and in-plain strain. Various prototypes that have been made using these concepts will be presented.Architectural Engineering +TechnologyArchitecture and The Built Environmen

Flexibles Schalungssystem für zweifach gebogene Betonfertigteile

Die Herstellung von zweifach gebogenen Betonfertigteilen ist aufgrund der hohen Kosten und der begrenzten Wiederverwendbarkeit der eingesetzten Schalung oder Formen nach wie vor kostspielig. Das Ziel eines kürzlich an der Technischen Universität Delft angelaufenen PhDProjekts ist die Entwicklung eines Produktionsverfahrens ohne jene schwierigkeiten mittels mehrfachen Schalungseinsatzes. Außerdem soll durch eine flexible Anpassungsfähigkeit der Schalung an die entsprechende Formgebung eine Optimierung erzielt werden. Im Beitrag werden das Forschungsziel und die Verfahrensweise des PhD-Projekts beschrieben.Design and ConstructionCivil Engineering and Geoscience

Innovative Ways of Dealing with Existing Problems: How to reliably Assess the Cause of Damage of Masonry Structures in an Area with Man-induced Earthquakes?

Groningen, a province in the northern part of the Netherlands, suffers from earthquakes because of gas drilling. The residential building stock in Groningen was not designed for these loads. Over the years a lot of smaller and larger damage has developed, possibly - but not necessarily - caused by the effects of gas drilling. Delft University of Technology was asked by the Dutch government to come up with a method to reliably assess the cause of damage of masonry structures in Groningen. This paper discusses the developed approach for reliably assessing the causes of failure of masonry structures in earthquake-prone areas and the way innovative monitoring techniques were applied.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Applied Mechanic

Manufacturing Double Curved Precast Concrete Panels using a Flexible Mould

Free form architecture with complex geometry brings along new challenges for manufacturers of building components. This paper describes the application of structural mechanics to predict the behaviour of an elastic mould surface, used as formwork for the manufacturing of double curved panels in precast concrete. Results are presented of laboratory experiments with a formwork to validate the model. The authors demonstrate that the model together with the mould prototype enable a flexible yet straightforward production method for curved concrete products that is applicable in many free form architecture projects nowadays.Structural and Building EngineeringCivil Engineering and Geoscience

Bundeling van zonlicht door gekromde gevels: Een concreet probleemgeval onderzocht met parametrische tools, simulatie en controlemetingen

Wat te doen als je prachtige gekromde glazen gevel onverwacht als vergrootglas blijkt te werken? Het fenomeen, dat al enigszins bekend was van de beruchte “Walkie Talkie” in Londen, is al eens eerder beschreven in Bouwfysica in 2018 [1]. Helaas kon dat artikel niet voorkomen dat ook in Nederland dit probleem vorig najaar plotseling optrad bij een nieuw gebouw dat op het punt stond opgeleverd te worden. Smeltende auto-onderdelen op het ondergelegen parkeerterrein, mogelijk gevaar voor bezoekers en een ongeruste opdrachtgever waren het resultaat. Parametrische tools en software voor simulatie van bezonning hielpen het ontwerpteam en de opdrachtgever om samen te zoeken naar de meest geschikte oplossing.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Applied MechanicsEnvironmental & Climate Desig

Manufacturing double-curved elements in precast concrete using a flexible mould: First experimental results

The manufacturing of double-curved precast concrete elements is still expensive, due to the high costs and limited possibilities for repetitive use of the moulds or formwork. The goal of the research described in this paper is to develop a production method that overcomes these difficulties by enabling the mould to be reused many times and by making the shape of the mould adjustable in a flexible way. First the paper gives an introduction of free-form architecture and the issues related to realizing complex geometry in concrete. Sequentially, the paper reports on the structural mechanics models that have been developed to accurately describe the behaviour of a flexible mould material. Finally laboratory experiments are reported, that are based on the concept of deforming an initially flat concrete element into a curved shape after a short initial hardening period. After this deformation process further hardening will take place in the final curved shape. The advantages of starting with an initial flat layer are that no contra-mould is needed, the element thickness can be controlled accurately and the casting process is relatively quick and simple.Design and ConstructionCivil Engineering and Geoscience